CCAPP Seminars
part of Coadd images with a cluster highlighted

Analysis of Galaxy clusters in the SDSS Coadd data

2/8/10
Marcelle Soares-Santos
(U. of São Paulo)

Galaxy cluster counts in spatial pixels and mass bins constitute a sensitive probe for Cosmology. Analyses based on this fact are part of the scientific program of experiments such as the upcoming Dark Energy Survey and have been pursued using the state of the art data. We perform a measurement of cosmological parameters using cluster counts in the SDSS Coadd. A measurement using clusters requires galaxy photometric redshifts, cluster finding algorithms, cluster mass calibration, cosmological parameter estimation and a data set of sufficient scope. For the SDSS Coadd, photometric redshifts are obtained with a neural network algorithm. A cluster catalog from this sample of 13M galaxies covering 250 sq-degrees up to redshift ~1 is constructed using a Voronoi Tessellation cluster finder. The selection function is computed using DES mock galaxy catalogs. A weak lensing analysis provides the mass calibration of the cluster sample binned into observables. A joint likelihood method using the mean abundance and spatial distribution is used to obtain cosmological constraints.

Cosmic ray anisotropy measurement with IceCube

2/9/10
Rasha Abbasi
(U. of Wisconsin, Madison)
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IceCube is cubic kilometer scale neutrino observatory located at the geographical South Pole. The kilometer cubed detector construction is on schedule to be completed in 2011. At the moment it is taking data with 59 deployed strings, when completed it will comprise 80-strings plus 6 additional strings for the low energy array Deep Core. The strings are deployed in the deep ice between 1,450 and 2,450 meters depth, each string containing 60 optical sensors. In this talk I will present selected results of ongoing analysis of IceCube detector data including the search reporting the measurement of 0.06% of large scale anisotropy. The data used in the large scale anisotropy analysis contains billions of downward going muon events with a median energy per nucleon of ~14 TeV and a median angular resolution of 3 degrees. The energy dependence of this anisotropy is also presented. The observed anisotropy has an unknown origin and we will discuss various possible explanations. Studies of the anisotropy could further enhance the understanding of the structure of the galactic magnetic field and possible cosmic ray sources.

Two galaxies

Unraveling the Formation History of Elliptical Galaxies

3/2/10
TJ Cox
(Carnegie Observatories)
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The idea that galaxies in general, and elliptical galaxies in particular, are shaped by their merger history has gained widespread acceptance. However, a detailed mapping between specific merger histories, and the wide variety of galaxies observed is still uncertain. By using a comprehensive set of state-of-the-art numerical simulations, we show that a single disk-disk merger, as originally proposed by the "merger hypothesis," is a plausible mechanism to form many elliptical galaxies provided that dissipation is involved. We also show that additional (merger?) processes are likely needed to form the largest ellipticals and we outline several properties commonly observed in elliptical galaxies that may provide insight into their formation history.

Understanding Core-Collapse Supernovae in the Transient Era

3/16/10
Chris Fryer
(Los Alamos National Laboratory)

Supernova surveys have taught us much about supernovae. But the surveys of the past focused on "normal" supernovae. Today's transient surveys are discovering a wide variety of stellar explosions. These new explosions potentially will teach us as much about supernovae as focused supernovae. I will discuss a variety of specific examples where we can use the "new" explosions discovered in transient surveys to help us understand supernovae.

Observations of Prompt Gamma-ray Burst Emission

3/30/10
Takanori Sakamoto
(NASA-GSFC)

I will review prompt emission observations from HETE-2 and Swift, which are both satellite missions dedicated to the detection of Gamma-ray Bursts (GRBs). HETE-2 and Swift have on-board computers to process the data and localize GRBs in real-time without a "human-in-the-loop" delay. Thanks to the fast and accurate position localization of GRBs, our understanding of their afterglow emission and host galaxies (birthplace of GRBs) has been dramatically improved. However, the origin of GRB prompt emission is still far from being resolved. I will talk about the observational properties of the prompt GRB emission phase in the context of HETE-2 and the Swift data. I will also discuss the nature of future observations needed to understand GRB prompt emission.

Unraveling gamma-ray Blazars in the Era of Fermi and VERITAS

4/6/10
Luis Reyes
(U of Chicago)

The field of high-energy astrophysics is experiencing a revolution due to recent observations that have revealed a universe that is surprisingly rich, variable and complex at gamma-ray energies. This revolution has now switched into high gear with the launch of the Fermi Gamma-ray Space Telescope and the full-fledged operation of a new generation of ground-based instruments such as VERITAS, H.E.S.S. and MAGIC. Among the different classes of gamma-ray sources observed by these instruments, a particular subset of active galactic nuclei (AGN) known as blazars stand out as some of the most energetic and variable objects observed at any wavelength. In my talk I will describe how the complementary capabilities of space and ground-based instruments are leading us to a better understanding of gamma-ray blazars as high-energy sources, as a population, and as a cosmological tool to probe the background radiation known as extragalactic background light (EBL). Finally, I will discuss the important scientific return that a next-generation instrument such as AGIS would bring to the field of AGN astrophysics.

NIght Sky

Clues about Dark Matter: Studying the Milky Way in 6-D

4/27/10
Nitya Kallivayalil
(MIT)

Tidal Streams provide a powerful probe of the potential of the Milky Way halo over large Galactocentric distances and their detailed phase-space structure gives us clues as to the nature of dark matter. Powerful theoretical techniques are now available to re-construct the underlying potential from the six-dimensional phase-space parameters that describe stellar tracers. Notably absent from the presently available data-sets are full 3-D velocities. I will describe ongoing efforts to remedy this aimed at tracers that sample the Milky Way halo at a large range of distances: the inner stellar halo, the Sagittarius Stream and Globular Clusters, and the Magellanic Clouds. I will also describe efforts to expand the number of reference QSOs suitable for space-based astrometry, and what we ultimately hope to learn about halo shape and distribution.

galaxy cluster simulation

Measuring gravitational lenses

5/18/10
Peter Melchior
(Heidelberg University)

With current and upcoming lensing surveys, massive datasets are or will become available, which enable us to constrain the cosmological parameters governing the formation of gravitationally bound structures in the universe. I will discuss the principles employed for inferring the mass distribution of individual galaxy clusters and of the large-scale structure as a whole. I will also go through the problems we encounter, especially in estimating the lensing-induced distortions from background galaxies, and how we seek to overcome them with novel methods and dedicated simulations.

Bullet Cluster

Cosmological Constraints from the Growth of X-ray Luminous Galaxy Clusters

5/25/10
Adam Mantz
(NASA/GSFC)

Over the past few years, constraints on the growth of cosmic structure have become available from observations of the galaxy cluster population and its evolution. This advance is largely due to the painstaking identification of clusters at redshifts z>0.3 in the X-ray flux-limited ROSAT All-Sky Survey (with ongoing Sunyaev-Zel'dovich and optical surveys not far behind). I will present cosmological constraints obtained from a sample of 238 X-ray flux-selected clusters, which, including the recently released MACS sample, extend to redshift 0.5. The cluster data provide robust constraints on the amplitude of the matter power spectrum as well as the dark energy equation of state (+-0.2 for a constant w model). The ability to trace the growth of structure as a function of time also allows us to test the observed growth rate against that predicted by General Relativity, independent of the background expansion history. Ultimately, this provides a tool for testing alternative theories of gravity and potentially distinguishing them from dark energy models. Finally, I will present constraints on cluster mass-observable scaling relations, a necessary and parallel aspect of the cosmological tests, which has some interesting implications for future work.

Exploring the Ends of the Rainbow: Cosmic Rays in Star-Forming Galaxies

9/21/10
Brian Lacki
OSU/CCAPP
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The cosmic rays (CRs) in star-forming galaxies dominate their emission at gamma-ray and radio wavelengths. The observed linear correlation between the nonthermal radio emission and the thermal infrared emission of galaxies, the far infrared (FIR)-radio correlation (FRC), links together the CR electron population, star-formation rate, and magnetic field strength of galaxies. Furthermore, gamma-ray data links the CR proton population, the star-formation rate, and gas density. We construct one-zone steady-state models of cosmic ray (CR) spectra in star-forming galaxies ranging from normal galaxies to the densest starbursts, calculating both the radio and gamma-ray emission. We then calculate the broadband emission of primary and secondary CR protons, electrons, and positrons. We find the FRC is caused by conspiracies of several factors for galaxies across the range of the correlation, including CR escape from galaxies, UV opacity, non-synchrotron cooling, and secondary electrons and positrons generated by CR protons. The conspiracies have great implications for the evolution of the FRC at high z, actually preserving it to higher redshift than previously thought but allowing variations in the FIR-radio ratio with different galaxy properties. I describe how the recent gamma-ray observations of M82 and NGC 253 compare with our models. These starbursts are somewhat less gamma-ray bright than we expect, but still indicate substantial pionic losses for CR protons and non-synchrotron cooling for CR electrons and positrons, supporting the conspiracy. Finally, I will describe our more recent work on the highest energy CR electrons in starbursts and the gamma-rays they produce. Starburst galaxies ought to be opaque to 30 TeV gamma-rays through pair production; in the strong magnetic fields of starbursts, these created electrons and positrons radiate synchrotron X-rays. We find that these synchrotron X-rays could make up ~10% of the diffuse hard X-ray emission from M82-like starbursts and even more in the brightest starbursts like Arp 220.

Electromagnetic Flares from the Tidal Disruption of Stars by Massive Black Holes

9/28/10
Linda Strubbe
(Berkeley)
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A star that wanders too close to a massive black hole (BH) gets shredded by the BH's tidal gravity. Stellar gas soon falls back to the BH at a rate initially exceeding the Eddington rate, releasing a flare of energy as gas accretes. How often this process occurs is uncertain at present, as is the physics of super-Eddington accretion (which is relevant for BH growth and feedback at high redshift as well). Excitingly, transient surveys like the Palomar Transient Factory (PTF), Pan-STARRS and LSST should shed light on these questions soon -- in anticipation, we predict observational properties of tidal flares. Early on, much of the falling-back gas should blow away in a wind, producing luminous optical emission imprinted with blueshifted UV absorption lines, and the observational signatures can be qualitatively different for M_BH ~ 105 - 106 Msun relative to more massive BHs. Possible X-ray emission can complicate the spectroscopic predictions. I will describe predicted detection rates for PTF, Pan-STARRS and LSST, and discuss the substantial challenge of disentangling these events from supernovae. These surveys should significantly improve our knowledge of stellar dynamics in galactic nuclei, the physics of super-Eddington accretion, the demography of IMBHs, and the role of tidal disruption in the growth of massive BHs.

Multi-wavelength studies of Galactic satellites and implications for dark matter detection

10/5/10
Louie Strigari
(Stanford/KIPAC)
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The census of local group dwarf galaxies has changed dramatically in recent years. By studying both their number counts and internal kinematics, faint Galactic satellites uniquely test the standard cosmological model and the properties of dark matter in a regime that is not probed by large scale observations such as the distribution of galaxy clusters and the cosmic microwave background. In this talk, I will discuss the confrontation of new data with theoretical predictions, highlighting a developling new twist on the lingering issue of the overproduction of Galactic satellites in the theory of cold dark matter. I will further discuss the importance of multi-wavelength probes of satellites, following a path of discovery in optical surveys, to targeted follow up spectroscopy of individual objects, and then to searches for particle dark matter annihilation using high energy gamma-rays and neutrinos. Following this trail I argue that Galactic satellites present the most robust constraints on the dark matter annihilation cross section. Given the current constraints, I will review the status of a search for optically dark satellites with the Fermi gamma-ray telescope.

The Coyote Universe and Beyond

10/12/10
Katrin Heitmann
(Los Alamos National Lab)
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Cosmological evidence for dark energy and dark matter poses an exciting challenge to fundamental physics. Next-generation surveys will investigate new physics beyond the Standard Model by targeting the nonlinear regime of structure formation, observed using powerful probes such as weak gravitational lensing. In order to fully exploit the information available from these probes, accurate theoretical predictions are required. Currently such predictions can only be obtained from costly, precision numerical simulations. In this talk, I will introduce the "Coyote Universe" project, a combined computational and statistical program to obtain precision predictions for the nonlinear power spectrum of density fluctuations. Such a program is essential for the interpretation of ongoing and future weak-lensing measurements to investigate and understand the nature of dark energy. I will discuss planned extensions of the Coyote Universe to include more cosmological parameters and physics. This work will be carried out with a new simulation capability recently developed at Los Alamos and targeted at future hybrid computing architectures. I will give a brief overview of these new developments.

IceCube

Neutrino Oscillations and (dis)appearance prospects for IceCube-DeepCore

10/19/10
Jason Koskinen
(Penn State)
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The recent commissioning of the full DeepCore sub-array, a low-energy extension of the IceCube neutrino observatory, offers exciting opportunities for neutrino oscillation physics in the multi-GeV energy region. The improved energy reach, use of the surrounding IceCube detector as an active veto and immense size of DeepCore will produce one of the largest neutrino datasets ever acquired, annually containing tens of thousands of atmospheric neutrinos after oscillating over a baseline of up to one earth diameter. I will cover some current non-DeepCore oscillation results as well as the prospects for a DeepCore muon neutrino disappearance and possibly a tau neutrino appearance measurement. Proposed future extensions to DeepCore designed to drive the energy reach down to ~1 GeV will conclude the talk.

Observational Signatures of Neutron Star Mergers

10/26/10
Brian Metzger
(Princeton U.)
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A fraction of neutron star (NS) and black hole binaries are formed sufficiently compact that they in-spiral and merge due to the emission of gravitational waves within the lifetime of the Universe. Such compact object mergers are among the most promising sources for the direct detection of gravitational waves with ground-based interferometers such as LIGO and Virgo. Maximizing the science of such a detection will, however, require identifying a coincident electromagnetic (EM) counterpart. One possible source of EM emission is a gamma-ray burst (GRB), powered by the accretion of material that remains in a rotationally-supported torus around the central black hole. I will overview the observational and theoretical status of the connection between NS mergers and the "short duration" subclass of GRBs. Although new observations from NASA's Swift observatory have provided some evidence in favor of the merger model, the puzzling discovery has also been made that many short GRBs are followed by late-time X-ray flaring activity, which does not fit current theory and may require modifying or considering alternative progenitor models. Another source of EM emission from NS mergers is a supernova-like optical transient, powered by the radioactive decay of heavy elements synthesized in neutron-rich ejecta from the merger. I will present the first calculations of the radioactively-powered transients from mergers that include both realistic nuclear physics and radiative transport, and I will discuss the prospects for detecting and identifying such events with present and future telescopes.

balloon above earth

The Cosmic Radio Background: Recent Measurement and Implications

11/2/10
Jack Singal
(SLAC/Stanford)

Results from the ARCADE 2 experiment reveal for the first time an extragalactic radio background that is brighter than some had assumed, in excess of the integrated contribution of discrete radio sources that have been characterized by interferometric surveys to their current flux limits. The origin of the radio background has thus provoked some debate. Given what is known from an analysis of radio source count surveys and constraints from the other cosmological backgrounds, we have developed a model to explain the radio background which has interesting astrophysical implications. This talk will combine experiment and theory. In the first part of the talk I will present the measurements performed by the balloon-borne ARCADE 2 experiment. In the second part, I will discuss how existing constraints disfavor some explanations of the radio background that have been proposed, and present the case that the background is produced largely by the radio emission of ordinary star forming galaxies above redshift 1 characterized by an evolving radio to far-infrared correlation.

QUIET experiment for CMB polarization measurement

11/8/10
Akito Kusaka
(U. of Chicago)

Cosmic microwave background (CMB) polarization is the ultimate probe of primordial gravity waves in the early universe, via the B-mode (or parity odd) signal on degree angular scales. A detection of such a signal would rule out most non-inflationary models and represent indirect observation of a fundamentally new phenomenon near the grand unification energy scale. With its unique radiometer technology, QUIET is among the most competitive experiments aiming to detect such a signature in the CMB. QUIET started its observation with its 44GHz receiver in October 2008. After nine months of successful observation, we deployed the 95GHz receiver replacing the 44GHz one and the observation resumed in August 2009. In this talk, I will review its instrumentation, site, and observation strategy, as well as the current status of the analysis.

The Cosmic Diffuse Gamma-ray Background: a puzzle to unveil

11/16/10
Marco Ajello
(SLAC/Stanford)
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The Extragalactic Gamma-ray background might encrypt in itself the signature of some of the most powerful and exotic phenomena in the Universe. Recently, Fermi-LAT measured its intensity with unprecedented accuracy. At the same time Fermi, with its unprecedented sensitivity, detected over a thousand point-like sources. Most of the extragalactic sources are blazars, but a growing fraction of the detected sources comprises also starburst/starforming galaxies as well as radio galaxies. In this talk I will review and address the current efforts to sort out the different components of the extragalactic gamma-ray background, focusing in particular on the blazar class and the starforming galaxies. I will also discuss future developments and the possibility to study the fluctuations of the gamma-ray sky to gain knowledge about the 'truly' diffuse component of the gamma-ray background. Finally I will also address the variability of the gamma-ray sky and what can be learned from its systematic study.

Resonant Stripping as the origin of dwarf spheroidal galaxies

11/23/10
Elena D'Onghia
(Havard-Smithsonian CfA)

The most dark matter dominated galaxies known are the dwarf spheroidals, but their origin is still uncertain. The recent discovery of ultra-faint dwarf spheroidals around the Milky Way further challenges our understanding of how low-luminosity galaxies originate and evolve because of their even more extreme paucity of gas and stars relative to their dark matter content. By employing numerical simulations I will show that interactions between dwarf disc galaxies can excite a gravitational resonance that immediately drives their evolution into spheroidals. This effect, which is purely gravitational in nature, applies to gas and stars and is distinct from other mechanisms which have been proposed up to now to explain the origin of dwarf spheroidals, such as merging, galaxy-galaxy harassment and more general heating processes, or tidal and ram pressure stripping. Using a new analytic formalism we developed based on the linear perturbation theory I will show the nature and the efficiency of the resonant process and its applicability to the formation of tails of stars and streams of gas.

The Fermi LAT as a cosmic-ray electron observer

11/30/10
Francesco Loparco
(U. of Bari, Italy)
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Even though it was designed to be a high sensitivity gamma-ray observatory, the Large Area Telescope (LAT) onboard the Fermi satellite has proved to be also an excellent electron/positron detector. The data collected by the LAT during its first year of operation have been used to measure the cosmic-ray electron and positron (CRE) energy spectrum in the energy range from 7 GeV to 1 TeV and to search for possible anisotropies in their arrival directions. An overview on the data analysis will be given and the main results will be illustrated.

Ultra High Energy Cosmic Rays from Mildly Relativistic Supernovae

12/7/10
Sayan Chakraborti
(Tata Institute)

Understanding the origin of the highest energy cosmic rays, is a crucial step in using them as probes of new physics, at energies unattainable by terrestrial accelerators. However their sources remain an enigma nearly half a century after their discovery. They must be accelerated in the local universe, as otherwise background radiations would severely suppress the flux of protons and nuclei, at energies above the Greisen-Zatsepin-Kuzmin (GZK) limit. Nearby GRBs, Hypernovae, AGNs and their flares, have all been suggested and debated in the literature as possible sources. A local sub-population of type Ibc supernovae with mildly relativistic ejecta have been detected for some time as sub-energetic GRBs or X-Ray Flashes and more recently as radio afterglows without detected GRB counterparts, such as SN 2009bb. In this talk we shall discuss the measurement of the size-magnetic field evolution, baryon loading and energetics, of SN 2009bb using its radio spectra obtained with the VLA and GMRT. This will allow us to see where the engine-driven SNe lie in the Hillas diagram and whether they can explain the post-GZK UHECRs?

A Bayesian Analysis of a Milky Way Ultra-Faint Satellite

1/18/11
Greg Martinez
(UC Irvine)

With the advent of SDSS the number of known Milky Way satellites has more than doubled. There new members, such as Segue 1, are extremely optically faint. Accurate mass measurements require careful analysis of velocity data. Here I describe the analysis of the multi-epoch velocity measurements of Segue 1 to determine its intrinsic velocity dispersion. Our method includes a simultaneous Bayesian analysis of both membership probabilities and the contribution of binary orbital motion to the observed velocity dispersion. Our analysis strongly disfavors the possibility that segue 1 is a bound star cluster. The inferred dark matter density is one of the highest measured, making Segue 1 a prime source for indirect dark matter detection. I will discuss the possibility of indirect detection in the context of SUSY models.

A Search for Point Sources with the IceCube Neutrino Observatory

2/1/11
Jon Dumm
(UW Madison)
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Construction of the IceCube Neutrino Observatory was only recently completed on Dec 18, 2010. IceCube is the first 1km3 detector of it's kind, monitoring 1 billion tons of ice. Deep under the South Pole, IceCube looks for rare high energy neutrino interactions (> ˜100 GeV). While the observatory was under construction for 5 years, data was being collected and analyzed continuously. Some of the science highlights so far include searches for astrophysical neutrinos, a measurement of the atmospheric neutrino spectrum above 1 TeV, observation of a cosmic ray anisotropy in the southern hemisphere, and indirect searches for dark matter. This talk will describe IceCube, the motivations for building such a detector, and highlight the effort to find point-like sources of astrophysical neutrinos.

detector schematic

Channeling and daily modulation in direct dark matter detectors

2/8/2011
Nassim Bozorgnia
UCLA

The channeling of the ion recoiling after a collision with a WIMP in direct dark matter detectors produces a larger signal than otherwise expected. Channeling is a directional effect which depends on the velocity distribution of WIMPs in the dark halo of our galaxy, and could lead to a daily modulation of the signal. I will discuss channeling and blocking effects using analytic models produced in the 1960's and 70's, and present estimates of the expected amplitude of daily modulation in the data already collected by the DAMA experiment.

Dark matter annihilation and spherical harmonics of Fermi gamma-rays

2/15/11
Dmitry Malyshev
(NYU)

Gamma-ray production by dark matter annihilation is one of the most universal indirect dark matter signals. In order to avoid intensive astrophysical background, one can study the gamma-rays away from the Galactic plane. The problems is that the dark matter annihilation signal at high latitudes is smooth and most probably subdominant to Galactic and extragalactic fluxes. I will discuss the use of spherical harmonics decomposition as a tool to distinguish a large scale small amplitude dark matter signal from astrophysical fluxes. The sensitivity of this method for currently available Fermi data is similar to the signal from thermal WIMP dark matter annihilation into, e.g., W+W-

Vagins and Beacom

GADZOOKS! How to See Extragalactic Neutrinos By 2016

3/8/11
Mark Vagins
(IPMU/UCI)
(Download Seminar PDF)

Water Cherenkov detectors have been used for many years to study neutrino interactions and search for nucleon decays. Super-Kamiokande, at 50 kilotons the largest such underground detector in the world, has enjoyed over ten years of interesting and important physics results. Looking to the future, for the last eight years R&D on a potential upgrade to the detector has been underway. Enriching Super-K with 100,000 kilograms of a water-soluble gadolinium compound - thereby enabling it to detect thermal neutrons and dramatically improving its performance as a detector for supernova neutrinos, reactor neutrinos, atmospheric neutrinos, and also as a target for the new T2K long-baseline neutrino experiment - will be discussed.

Generative modeling for the Milky Way and the Universe

3/14/11
Jo Bovy
(New York University)

At the interface between observational and theoretical astrophysics lies data analysis and inference. The most accurate and precise inferences require using a model that generates the data and that takes the noise into account. I give two examples where generative modeling performs better than other methods for parameter inference and classification. To put the Milky Way in a cosmological context we want to know its mass and dark matter distribution in detail. I will discuss in general how we can infer the gravitational potential—dynamics—from kinematics alone. As an application of this, I show how we can determine the Milky Way's circular velocity at the Sun from maser kinematics. As a second example, I discuss density-estimation-based classification for target selection. SDSS-III's BOSS aims to observe 150,000 quasars down to the faint limit of the SDSS in a redshift range (2.2 <= z <= 3.5) where the quasar and stellar color loci overlap significantly. I will show how we can determine models of the underlying distribution of quasars and stars in flux space. We can use these models to evaluate quasar probabilities for all potential targets and build an efficient survey.

Energy-Dependent Composition of UHECRs and the Future of Charged Particle Astronomy

3/29/11
Antoine Calvez
(UCLA)
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Recent results from the Pierre Auger Observatory show an energy dependent chemical composition of ultrahigh-energy cosmic rays (UHECRs), with a growing fraction of heavy elements at high energies. These results suggest a possible non-negligible contribution from galactic sources. We show that in the case of UHECRs produced by gamma-ray bursts (GRBs), or by rare types of supernova explosions that took place in the Milky Way in the past; the change in the composition of the UHECRs can be the result of the difference in diffusion times between different species. The anisotropy in the direction of the Galactic Center is expected to be a few per cent on average, and the locations of the most recent/closest bursts can be associated with observed clustering of UHECRs.

Light WIMPs!

4/12/11
Dan Hooper
(U. of Chicago)
(Download Seminar PDF)

Observations from the direct detection experiments DAMA/LIBRA and CoGeNT, along with those from the Gamma Ray Space Telescope, have been interpreted as possible evidence of dark matter in the form of relatively light (5-10 GeV) WIMPs. I will discuss the implications of these observations for dark matter phenomenology and discuss how it will be possible with future measurements to either confirm or refute this interpretation. I will also discuss how recent results from the Tevatron could impact efforts to build models including a light WIMP.

Optimal Linear Image Combination

4/19/11
Barnaby Rowe
(Jet Propulsion Laboratory/Caltech)

I will describe a simple, yet general, formalism for the optimized linear combination of astrophysical images, developed here at JPL/Caltech with Christopher Hirata and Jason Rhodes. The formalism allows the user to combine multiple undersampled images to provide oversampled output at high precision. The proposed method is general and may be used for any configuration of input pixels and point spread function; it also provides the noise covariance in the output image along with a powerful metric for describing undesired distortion to the image convolution kernel. The method explicitly provides knowledge and control of the inevitable compromise between noise and fidelity in the output image.

We also present a first prototype implementation of the method then put it to practical use in reconstructing fully-sampled output images using simulated, undersampled input exposures that are designed to mimic the proposed dark energy mission WFIRST. Comparing results for different dither strategies we illustrate the use of the method as a survey design tool. Finally, we use the method to test the robustness of linear image combination when subject to practical realities such as bad pixels and focal plane plate scale variations, an important consideration for a mission such as WFIRST.

A Quest for Sources of Ultrahigh Energy Cosmic Rays

4/26/11
Kumiko Kotera
(U. of Chicago)
(Download Seminar PDF)

The origin of ultrahigh energy cosmic rays (UHECRs) has not been unveiled in spite of decades of experimental and theoretical research. In this talk, I discuss the observable signatures that would constrain the possible sources to one single suspect.
In particular, I will present the anisotropy signatures expected for various types of sources, and describe how the intergalactic magnetic field plays a prominent role in this picture. For this purpose, I will introduce an analytical formalism to study the propagation of UHECRs in the magnetized Universe.
Another constraint on the sources might come from multi-messenger signatures (in gamma-rays, neutrinos and gravitational waves) that can be produced together with UHECRs. I will present the expected fluxes for various astrophysical scenarios and discuss to which extent these signals could pin-point the actual sources of UHECRs.
In light of this discussion, I will briefly present the latest results of the Pierre Auger Observatory and give requirements for future detectors in UHECRs, neutrinos, gamma rays and gravitational waves, to solve this long-standing enigma.

21cm Slices

Constraining the Dawn of Cosmic Structure and the Epoch of Reionization with the 21cm Line

5/3/11
Jonathan Pritchard
Harvard/CfA

The first billion years of the Universe contains the formation of the first galaxies and reionization. This period lies beyond the current observational frontier presenting challenges to theory and observation. Low frequency observations of the redshifted 21 cm line of neutral hydrogen will be key in developing our understanding of this period. In this talk, I will describe two aspects of the 21 cm signal from the period of "cosmic dawn": the global 21 cm signal and 21 cm fluctuations. I will discuss what can be learnt about the first galaxies and reionization from this technique and explore some of the challenges and opportunities ahead for the first observations.

Indirect Detection of Dark Matter -
Electroweak Bremsstralung and Other Stories

5/13/11
Nicole Bell
(University of Melbourne)
(Download Seminar PDF)

Annihilation of dark matter to fermionic final states is often either helicity or velocity suppressed. We outline the circumstances under which bremsstrahlung processes can remove such suppressions, thereby dramatically improving prospects for indirect detection. In these cases, the three body final states such as e+e-gamma, e+e-Z and e\nuW dominate over the 2-body annihilation modes. Since the W and Z gauge boson have large hadronic decay modes, purely leptonic annihilation is impossible if the 3-body bremsstrahlung processes dominate. We also discuss dark matter annihilation via metastable mediators, and show that this can lead to greatly enhanced high energy neutrino signals from the Sun.

miguel

The High Altitude Water Cherenkov Gamma-ray Observatory

5/24/11
Miguel Mostafa
(Colorado State U.)

The High Altitude Water Cherenkov (HAWC) experiment is a large field of view, continuously operated TeV gamma-ray observatory to be constructed using a dense array of water Cherenkov detectors covering an area greater than 25,000 m2. HAWC will be located at an elevation of 4,100 m near the Sierra Negra mountain in Mexico. The instrument will use 900 photomultiplier tubes to observe the relativistic particles and secondary gamma rays in extensive air showers. This technique has been used successfully by the Milagro observatory to detect known (as well as new!) TeV sources. HAWC is a natural extension of Milagro, which has demonstrated the ability to detect {at TeV energies{ many of the galactic sources which have been observed by the Fermi LAT in the GeV energy range. The design of HAWC was optimized using the lessons learned from Milagro, and will be 15 times more sensitive than Milagro when completed. Improvements in sensitivity, angular resolution, and background rejection will allow HAWC to measure or constrain the TeV spectra of most of the Fermi discovered GeV sources. In addition, above 100 GeV, HAWC will be more sensitive than the Fermi satellite and be the only ground-based instrument capable of detecting prompt emission from gamma-ray bursts in this energy regime. In this seminar I will present the physics motivation, the HAWC observatory, and the activities of my group.

Supernova Feedback Keeps Galaxies Simple

9/26/11
Sayan Chakraborti
(TIFR, India)

Galaxies are complicated and history dependent. Yet, recent studies have uncovered surprising correlations among the properties of galaxies. Such simplicity seems, naively, to be at odds with the paradigm of hierarchical galaxy mergers. One of the puzzling results, is the simple linear correlation between the neutral hydrogen mass and the surface area, implying that widely different galaxies share very similar neutral hydrogen surface densities. We shall see in this presentation that self-regulated star formation, driven by the competition between gravitational instabilities and mechanical feedback from supernovae, can explain the nearly constant neutral hydrogen surface density across galaxies.

Shape Image

Weak Lensing Simulations and Precision Cosmology with Large-area Sky Surveys

9/27/11
Matt Becker
(KICP/U. of Chicago)

Weak lensing measurements are an essential part of near- and long-term large-area sky surveys aimed at an array of scientific goals, like understanding Dark Energy, elucidating further the connection between galaxies and dark matter halos, constraining modifications to General Relativity, etc. The weak lensing community has undertaken extensive simulation efforts, both CCD image simulations and computations of the cosmological weak lensing signals from large-scale structure simulations, in order to address the variety of systematic errors which can adversely effect these measurements and their interpretation. The next logical step in this effort is the construction of mock galaxy catalogs with weak lensing shear signals self-consistently from large-scale structure simulations. While these weak lensing mock galaxy catalogs have easily been made for small patches of sky (~10 square degrees), upcoming large-area sky surveys will image thousands of square degrees or more. I will describe a new multiple-plane ray tracing code which is able to produce full-sky weak lensing deflection, convergence, and shear fields suitable for the construction of weak lensing mock galaxy catalogs for large-area sky surveys. I will also highlight the application of this code to the Dark Energy Survey simulation effort. Finally, I will present a prototypical example of these simulation efforts, my recent work on interpreting weak lensing galaxy cluster mass measurements, emphasizing understanding their scatter and more importantly their potential biases. This work, and ongoing work by others in the Dark Energy Survey collaboration based on these new weak lensing mock galaxy catalogs, illustrates the utility these simulations in understanding systematic errors in current and future weak lensing measurements from large-area sky surveys.

radio halos and relics explained as arising from one homogeneous population of cosmic-ray protons

The Intracluster Medium of Galaxy Clusters

10/11/11
Uri Keshet
(CfA, Harvard)

Recent observations of galaxy clusters reveal new insights into the dynamical and nonthermal processes in the intracluster medium (ICM). Tangential discontinuities are directly seen in high resolution X-ray maps of cool cluster cores, in the form of cold fronts. They reveal bulk shear flows which magnetize the plasma, give rise to radio minihalos, and may play a key role in solving the cooling problem. The ICM shows a rich phenomenology of non-thermal radio emission, arguably arising from hadronic cascades involving cosmic-ray protons. While such a secondary signal is too weak to be observed by Fermi, the primary gamma-ray signal from strong virial shocks may be identifiable.

Dark Matter Parameters from Neutrino Telescopes

10/18/11
Katie Richardson
(U. of New Mexico)
(Download Seminar PDF)

In this talk, I will discuss how neutrino telescopes may help us extract dark matter parameters and can in fact place the most stringent bounds on the spin-dependent dark matter-nucleon scattering cross-section. In particular the dark matter annihilation final state provides a distinctive signature that allows us to discriminate among classes of dark matter models. Models with gauge boson or tau final states alongside neutrino final states are distinguishable, and the theoretically well-motivated U(1)_B-L extension of the MSSM produces just such a mixture of final states. It is feasible that the energy reconstruction capability of the IceCube neutrino telescope will preserve the important features. Finally, I will address the prospect for differentiating neutrino flavor final states from one another.

First Cosmic Shear Measurement in SDSS

10/25/11
Eric Huff
(Berkeley)
(Download Seminar PDF)

I discuss preliminary results from a first cosmic shear measurement in SDSS. We have coadded 250 square degrees of multi-epoch SDSS imaging along the celestial equator, optimizing for weak lensing measurement. We employ standard techniques for shape measurement, shear calibration, and inference of the redshift distribution, and perform a wide array of tests that show that the systematic errors for this measurement are probably negligible compared to the statistical errors. We analyze the shear autocorrelation with and without WMAP7 priors, and produce competitive constraints on the matter density and the amplitude of the matter power spectrum at redshift z=0.6.

I will also discuss some new results on lensing magnification. Motivated by the need for greater signal-to-noise in weak lensing measurements, we have used tight photometric galaxy scaling relations to measure a galaxy-galaxy magnification signal with many times the signal-to-noise of previous magnification results. I describe how minor improvements on this work may permit magnification measurements with signal comparable to shear.

Baryon Acoustic Oscillations:
Galaxy Bias Effect and Cosmological Measurements

11/1/11
Kushal Mehta
(Arizona)

I will talk about the work presented in Mehta et al (2011) regarding measuring the effects of galaxy bias on baryon acoustic oscillations (BAO) measurements in cosmological N-body simulations, and the technique of reconstruction used to refine the BAO signal. I will also talk about new SDSS-II LRG (Luminous Red Galaxies) BAO data and the measurements of cosmological parameters. These results will be presented in 3 papers (Padmanabhan et al, Xu et al, and Mehta et al, all in prep).

Propagation of Ultrahigh Energy Nuclei in the Galactic magnetic field

11/2/11
Gwenael Giacinti
(APC/Paris)

The composition of ultra-high energy cosmic rays (UHECR) at the highest energies is a matter of debate. The measurements from the Auger Observatory would suggest a shift towards heavier nuclei, whereas Telescope Array results can still be compatible with a proton composition. We present simulations for the propagation of ultra-high energy heavy nuclei, with E > 6x10^(19) eV, within recent Galactic Magnetic Field (GMF) models. Differences between the propagation of protons and heavy nuclei in the GMF may provide additional information about the charge composition of UHECRs.
For UHE heavy nuclei primaries, there is no one-to-one correspondence between their arrival directions at Earth and the directions of their extragalactic sources. We show the challenges, and possibilities, of "UHECR astronomy" with heavy nuclei. Finally, we present a quantitative study of the impact of the GMF on the (de-)magnification of source fluxes, due to magnetic lensing effects. For 60 EeV iron nuclei, sources located in up to about one fifth of the sky would have their fluxes so strongly demagnified that they would not be detectable at Earth, even by the next generation of UHECR experiments.

Exploring the Dark Universe with Gravitational Lensing

11/15/11
Sherry Suyu
(U. or California, Santa Barbara)
(Download Seminar PDF)

Understanding the nature of dark energy and dark matter is one of the biggest challenges in modern cosmology. Strong gravitational lens systems provide a powerful tool for measuring cosmological parameters and for probing dark matter in galaxies. In the first part of my talk, I will show how strong lens systems with measured time delays between the multiple images can be used to determine the "time-delay distance" to the lens. I will present the cosmological constraints, particularly on the Hubble constant and the dark energy equation of state, from a detailed analysis of the gravitational lens B1608+656, and discuss future prospects of time-delay lens cosmography. In the second part of my talk, I will present a joint lensing and kinematics analysis of the spiral gravitational lens B1933+503 at z=0.76 to disentangle the baryons and dark matter in the spiral galaxy and probe the stellar initial mass function.

Understanding Star-forming Galaxies across Cosmic Time

11/21/11
Matt Bothwell
(U. of Cambridge, UK)

The formation of stars from the interstellar medium is one of the primary drivers of galaxy evolution, and obtaining a full characterization of the processes involved is essential if we are to understand the physics behind the formation of galaxies. Viewing galaxies at high redshift gives us a direct window into the various formation processes, but the importance of a comprehensive understanding of the z~0 Universe cannot be overemphasized, as the early stages of galaxy evolution leave telltale footprints in the properties of local galaxies. I present work examining the star formation laws in galaxies at both low and high redshift. Firstly, I discuss the distribution function of star formation in the local Universe, calculated in a manner analogous to the luminosity function, and its implications for galaxy formation scenarios.

Looking to high redshift, I present molecular gas observations of a sample of z~2 ultra-luminous infrared galaxies (ULIRGs). These observations provide the best view of the star formation and kinematic properties of these enigmatic systems, allowing us to place them into the context of galaxy formation models.

Core Collapse Supernovae: Black Holes and Neutrinos

11/29/11
Evan O'Connor
(Caltech)

Core-collapse supernovae are some of the most explosive high-energy astrophysical events in our universe. They are the result of the collapse of the iron core in an evolved massive star (M > 8-10 solar masses). The collapse is halted when the collapsing core reaches nuclear densities, at which point the core-collapse supernova central engine takes over. We know that the central engine must eventually drive an explosion in some fraction of massive stars, however, after over 40 years of theoretical research we still do not completely understand this core-collapse supernova mechanism. In this talk, I will review the state of core-collapse supernova theory. I will also discuss our work at Caltech on both the success and failure of the core-collapse supernova mechanism. For looking at the success, we considered the possibility that collective neutrino oscillations may enhance the neutrino mechanism. If a core-collapse supernova fails, a black hole is the result. I will discuss our predictions for black hole populations from failed supernova.

Beyond the Standard Model of Cosmology:
Dark Energy, Neutrinos, and Primordial Non-Gaussianity

12/6/11
Shahab Joudaki
(UCI)
(Download Seminar PDF)

Some of the most outstanding problems of physics lie in the understanding of the dark sector of the universe, in particular dark energy, neutrinos, and inflation.
The dark energy and neutrinos are correlated through their effects on distances and the clustering of matter. I will review the present state of surveys sensitive to the effects of dark energy and neutrino mass. I will then forecast how well the present dark energy density and its equation of state along with the sum of neutrino masses may be constrained using multiple probes that are sensitive to the growth of structure and expansion history, in the form of weak lensing tomography, galaxy tomography, supernovae, and the cosmic microwave background. I will include all cross-correlations between these different probes and allow for non-negligible dark energy at early times (motivated by the coincidence problem) in spatially flat and non-flat cosmological models. In the latter portion of the talk, I will discuss a novel method to constrain non-Gaussianity of the primordial density perturbations by its impact on the ionization power spectrum from 21 cm emission during the epoch of reionization. I will show that 21 cm experiments in the near future may constrain inflationary models via primordial non-Gaussianity to the same precision as expected from Planck.

The LHCf experiment: Verification of high energy cosmic ray interactions

1/10/12
Yoshitaka Itow
(Nagoya University)
(Download Seminar PDF)

Recent progress in air shower observations of the highest energy cosmic rays with $\sim 10^{20}$ eV gives us an enigmatic problem about their origins and propagations. One difficulty is implication of air shower observations due to uncertainty of hadron interactions in such high energy. The particle production at the very forward region plays an important role in air shower development, since it carries most of collision energy. The LHCf experiment is dedicated to measure spectra of neutral particles at very forward region of the LHC collision point in order to verify interaction of cosmic rays of 10^{17} eV. The data taking had been carried out for $\sqrt{s}$=0.9TeV and 7TeV. The results of "inclusive" gamma-ray energy spectra at 0 degree has been obtained. Future plan for very forward measurement at p-A or A-A collisions is also discussed.

Adventures in dark-matter astrophysics

1/30/12
Annika Peter
(U. of California, Irvine)

From astronomical observations, we know that dark matter exists, makes up 23% of the mass budget of the Universe, clusters strongly to form the load-bearing frame of structure for galaxy formation, and hardly interacts with ordinary matter except gravitationally. However, this information is not enough to identify the particle specie(s) that make up dark matter. As such, the problem of determining the identity of dark matter has largely shifted to the fields of astroparticle and particle physics. In this talk, I will review the current status of the astroparticle/particle-physics search for the nature of dark matter. Given the absence of detections in those experiments, I will advocate a return of the problem of dark-matter identification to astronomy, and show what kinds of theoretical and observational work might be used to pin down the nature of dark matter once and for all.

Understanding the cosmic recombination epoch

1/31/12
Chris Hirata
(Caltech)

The primary cosmic microwave background anisotropies have proven to be among the most useful cosmological probes, due to a combination of impressive observational advances and the simplicity of the underlying theory -- the CMB is a linear perturbation on a homogeneous and isotropic background. The most difficult part of the theoretical prediction for the primary CMB anisotropies has turned out to be the modeling of the cosmic recombination epoch: the transition from an ionized to neutral Universe, roughly 400,000 years after the Big Bang, which is the "surface" that we actually see when we look at the CMB. Even though the early Universe contained just three elements, computing its recombination history at the sub-percent level needed for Planck involves a maze of forbidden transitions, line escape processes, and radiative transfer in the far ultraviolet where the continuum opacity is dominated by multi-photon transitions in hydrogen (rather than by metals or dust). I will conclude by evaluating our current understanding of the recombination epoch and prospects for more direct tests of recombination models.

Signatures of Energy Injection in the Cosmic Microwave Background

2/7/12
Tracy Slatyer
(IAS)

Dark matter annihilation, or other new physics, could inject high-energy electrons and photons into the early universe after the redshift of last scattering, modifying the cosmic ionization history. In turn, this modification induces a characteristic perturbation to the anisotropies of the cosmic microwave background radiation. I will discuss how to describe an arbitrary energy injection history in terms of a few parameters that efficiently characterize the possible effects on the CMB. This approach allows very general constraints to be set on arbitrary models of energy injection from new physics.

Bounds on annual modulation signal in dark matter direct detection

2/15/12
Jure Zupan
(U. of Cincinnati)

I will show constraints on the annual modulation signal in Dark Matter direct detection experiments which assume only very general properties of dark matter halo. The derivation of the bound uses an expansion in the earth velocity and is expressed in terms of the unmodulated event rate. I will illustrate the bounds by applying them to the annual modulation signals reported by the DAMA and CoGeNT experiments in the framework of spin-independent elastic scattering. While the DAMA signal satisfies our bounds, severe restrictions on the DM mass can be set for CoGeNT. Finally, I will also review the constraints on light dark matter interpretation of the CRESST-II results.

The Renaissance of Radio Detection of Cosmic Rays

2/21/12
Tim Huege
(KIT)

In the 1960s, researchers at the Jodrell Bank Observatory in Manchester, UK discovered that cosmic ray air showers emit pulsed radio signals at MHz frequencies. After a decade of very active research, however, activities in the field ceased completely.
Since 2001, radio detection of cosmic ray air showers has experienced an impressive renaissance. The LOPES experiment in particular has pioneered a modern approach to cosmic ray radio detection using digital radio-interferometry. LOPES has confirmed that the radio emission is coherent, is of dominantly geomagnetic origin, and has great potential for large scale application complementing existing detection techniques for ultra-high energy cosmic rays. This potential is currently being evaluated with the Auger Engineering Radio Array (AERA), which in its final setup will consist of 160 antennas covering an area of 20 square kilometres.
In this talk, I will review the revival of the radio detection technique, describe its current status and open questions, and discuss its future development.

What Stars are Useful For - A Particle Physicist's Point of View

2/28/12
Alexander Friedland
(LANL)

Stars realize a variety of physical conditions inaccessible in the lab. Various stages of stellar evolution are influenced by microphysical processes that are sensitive to the fundamental properties of elementary particles. This makes it possible to use stars to search for new particle physics beyond the Standard Model. I will discuss what massive stars tell us about neutrino magnetic moments and axion particles. As a particularly amusing example of conditions that cannot be reproduced in the lab, I will also mention the phenomenon of collective oscillations of neutrinos streaming out of the supernova core.

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Double White Dwarf Binaries: Pre- and Post-meger

3/6/12
Tony Piro
(Caltech)
(Download Seminar PDF)

We now know of many white dwarf binaries in our Galaxy that will merge within a Hubble time due to gravitational wave emission. But there remains a lot of uncertainty in what will happen when the merger occurs. I will discuss theoretical work concerning the tidal interactions between the white dwarfs, how the tidal dissipation imprints itself on the inspiral, and the ramifications the tides have for the merger. Next I will explore the possible observational signatures expected when the total mass of the binary exceeds the Chandrasekhar limit, such as producing a Type Ia supernova or an accretion induced collapse to a neutron star. Such theoretical studies will aid current and future wide field, high cadence surveys that are revolutionizing our view of the transient sky.

Blowing Bubbles with Supernovae

PRICE PRIZE LECTURE
3/7/12
Sayan Chakraborti
(TIFR, India)

Our galaxy is full of gigantic bubbles. The distribution of gas in galaxies has often been compared to Swiss Cheese. But there is confusion about what is responsible for these bubbles? We shall discuss the role of supernovae in blowing bubbles.

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Gravitational Flexion: Facts and Opinions

3/13/12
Massimo Viola
(U. of Edinburgh)

Gravitational flexion, caused by derivatives of the gravitational tidal field, is potentially very important for the analysis of the dark matter distribution in gravitational lenses, such as galaxy clusters or the dark matter haloes of galaxies. Reliable flexion measurements, specially in large surveys like KiDS or EUCLID, can increase the accuracy with which the inner profile of galaxy clusters can be constrained or can support the detection of substructures, whose presence in galaxy clusters is a firm prediction of the Cold-Dark Matter cosmogony. However the measurement of this signal and its interpretation are not trivial. I will critically discuss all those aspects and I will present possible solutions.

Probing the origin, propagation & distribution of cosmic rays with the Fermi LAT

3/27/12
Markus Ackermann
(DESY)
(Download Seminar PDF)

The Fermi Large Area Telescope is a pair-conversion telescope designed to study gamma-rays between 20 MeV and several hundreds of GeV. Its large effective area, field-of-view and survey-mode observation strategy make it a unique instrument to study the gamma-ray emission from potential sources of cosmic rays, as well as the diffuse emission from the interactions of the cosmic rays with the interstellar gas and radiation fields. Even though it was designed as a gamma-ray telescope, the LAT is also very competitive in measuring directly the local cosmic-ray electron and positron intensities in the GeV energy range. Lacking an on-board magnet, the Earth magnetic field is used for charge separation in the energy range between 20 GeV and 200 GeV. I will review the results obtained during the LAT mission and their astrophysical implications.

Observational Probes of Cosmic Acceleration

4/3/12, 4/10/12
Michael Mortonson & David Weinberg
(OSU/CCAPP)
(Download Seminar PDF)

In this two-person, two-part seminar, we will cover highlights from our review article "Observational Probes of Cosmic Acceleration," by D. Weinberg, M. Mortonson, D. Eisenstein, C. Hirata, A. Riess, and E. Rozo (arXiv:1201.2434). The article describes the techniques that underpin ongoing and planned "dark energy experiments," including BOSS, DES, BigBOSS, LSST, and Euclid/WFIRST. The first seminar will cover motivation, theoretical background and parameterized models, Type Ia supernovae, baryon acoustic oscillations, and weak lensing. The second seminar will discuss galaxy clusters and (briefly) some alternative methods, then turn to performance forecasts for "Stage III" and "Stage IV" cosmic acceleration programs and the complementarity of different approaches.

Highly Eccentric Jupiters and Binaries

4/24/12
Boaz Katz
(IAS)

They are out there, they are detectible, and finding them may solve the problem of how hot Jupiters and tight binaries form.

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Any nu's from GRBs?

5/1/12
Markus Ahlers
(U. of Wisconsin, Madison)

Gamma ray bursts are among the prime suspects as the sources of ultra-high energy (UHE) cosmic rays (CRs). Not only are these objects capable of accelerating nuclei to the extreme energies so far detected but they can also supply enough power to sustain the energy density of UHE CRs. The production of high energy neutrinos would be an unavoidable consequence of the acceleration of nuclei in the presence of the intense radiation field of the GRB. The IceCube experiment has been looking for this neutrino emission associated with GRBs detected by the SWIFT and Fermi satellites between May 2008 and April 2010. Whereas typical models predict at least a few observable neutrinos during this period IceCube found none. I will discuss how this non-observation challenges the UHE CR paradigm of GRBs.

What do we know about the prompt emission in GRBs?

5/8/12
Asaf Pe'er
(Harvard-Smithsonian Center for Astrophysics)

Since the launch of Fermi in 2008, a prime focus had been given to understanding the physical origin of the prompt emission from gamma-ray bursts (GRBs). I will review recent Fermi results, and focus on some key, unsolved questions. I will then emphasis the role played by photospheric emission. In particular, I will explain various mechanisms that broaden the "Planck" spectrum that can potentially explain the observed spectra.

Cosmology with Absorption Line Systems

5/16/12
Michele Fumagalli
(Santa Cruz)

The study of absorption line systems in spectra of distant quasars offers a unique way to map the physical properties of hydrogen and metals in the intergalactic medium and in high-redshift galaxies. In this talk, I will use predictions from hydrodynamical cosmological simulations of high-redshift galaxies to discuss the prospects of studying inflows and outflows with absorption line systems. I will also present first results from an ongoing observational program that led to the discovery of pristine gas clouds at z=3 and I will discuss this finding in the context of Big Bang nucleosynthesis.

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Measuring the growth of structure and the expansion rate at z=0.57 in the SDSS-III Baryon Oscillation Spectroscopic Survey

5/22/12
Beth Reid
(LBL)

While the underlying clustering of galaxies is believed to be isotropic, two distinct effects change the relative amplitude of clustering along and perpendicular to the line of sight. The Alcock-Pacyznski effect allows a geometric test to measure the product of the angular diameter distance and Hubble expansion rate at the galaxy sample's redshift. Peculiar velocities of galaxies also amplify the apparent clustering along the line-of-sight. We demonstrate our ability to distinguish these effects in the data through their scale-dependence, and present measurements of both the growth of structure and the expansion rate at z=0.57 using data from the SDSS-III Baryon Oscillation Spectroscopic Survey.

Creation of Cosmic Structure in Clusters of Galaxies

5/29/12
Julian Merten
(Caltech/JPL)

Clusters of galaxies are a powerful tool to study the formation of structure in a cosmological context and to dissect the interaction between the different matter components. All main components of cosmic structure formation become accessible in those giants; luminous galaxies, the hot gas floating between them and the dark matter component, unraveled through gravitational lensing. Two main approaches are of special interest when studying the assembly of structure in clusters. In violent mergers, matter can be observed under extreme conditions and the cosmic bottom-up scenario becomes directly visible. In contrast, an understanding of a relaxed population at the end of its assembly sheds light on e.g. a universal density profile of dark matter structures. I will present both approaches with real observational programs, including the spectacular merger Abell 2744, dubbed "Pandora's Cluster", and the large HST multi-cycle treasury program CLASH. Powerful numerical techniques, including parallel GPU implementation to harvest those programs shall be discussed. In this context a comprehensive analysis of numerical simulations of individual clusters but also of large cosmological boxes is inevitable to compare observations to the theory of structure formation.

Weak-lensing measurements demystified

6/11/12
Peter Melchior (OSU/CCAPP)

I will explain what weak lensing is good for and how the measurements are actually done, review the current state of affairs and lay out why it is not sufficient for even the near future. I'll conclude with a possible solution.

Detection of GZK Neutrinos with Radio Detectors

6/11/12
Carl Pfendner (OSU/CCAPP)

The Greisen-Zatsepin-Kuzmin (GZK) hypothesis proposes that the the highest energy cosmic rays interact with the cosmic microwave background, creating a suppression of the flux of these ultrahigh energy particles. In the interaction, ultrahigh energy neutrinos would also be created, which would not be subject to the subsequent series of interactions over its propagation distance. There are several detectors being built which propose to detect these neutrinos through radio signals produced via the Askaryan effect. Their detection will help to confirm the GZK hypothesis as a mechanism of cosmic ray flux suppression. I will outline my current and future work in developing a couple of these new projects: the Askaryan Radio Array (ARA) and the ExaVolt Antenna (EVA). For ARA, I have been concentrating on merging simulation and reconstruction. For EVA, I have been working a simulation of the antenna for planning and design purposes.

Neutrino Hunt for Dark Matter in the Sun

6/26/12
Carsten Rott (OSU/CCAPP)

Despite overwhelming evidence that it composes the vast majority of the mass in the Universe, dark matter's particle properties literally remain in the dark. Identifying the mysterious nature of dark matter is one of today's most pressing scientific problems and is being sought for using colliders, direct-detection experiments, and powerful indirect techniques. The observation of a high energy neutrino flux from the Sun would be a smoking gun signature for self-annihilating dark matter and provides a high discovery potential. I will describe the current status of dark matter searches from the Sun and discuss the prospects for observing signals at current and next generation neutrino detectors.

Zooming in on in AGN Structure with Microlensing

6/26/12
Ana Mosquera (OSU/Astronomy)

The main observational problem for testing accretion disk models lies in the inability to resolve the emission regions of quasars, since no astronomical method allows us to direct imaging their central engine. In this talk I will review how gravitational microlensing provides a natural telescope to zoom in on in the regions closest to the SMBH and its implications.

Searching for Dark Matter in Galaxy Clusters using Neutrinos

7/3/12
Basudeb Dasgupta (OSU/CCAPP)

Galaxy clusters are rich in dark matter. Presence of dark matter substructures in galaxy clusters enhances the dark matter annihilation rate by orders of magnitude over the contribution from the smooth component of the dark matter distribution, and makes it spatially extended. We show that significant improvement in the experimental sensitivity to DM annihilation can be achieved at neutrino telescopes such as IceCube/KM3NeT by carefully optimizing the search for neutrinos from galaxy clusters, especially, if neutrino showers can be reconstructed, as may be possible in KM3NeT.

Searching for a New Window on a New Window to the Universe

7/3/12
Patrick Allison (OSU/Physics)

Between 10-100 EeV, ultrahigh energy cosmic rays (UHECRs) offer the possibility of charged particle astronomy in an energy regime that has been previously unexplored. However, the extremely low flux (1 per square kilometer per century) of cosmic rays at these high energies has limited science to only hints of the anisotropy expected from sparse astronomical accelerators. In addition, the two most successful methods for detecting cosmic rays - with a surface array and with air fluorescence detectors - are unlikely to be able to scale up to sufficiently large detectors to combat this low flux. Radio detection of cosmic rays in both the GHz and MHz emission have been the subject of considerable study in recent years, and offer the possibility of a new detector without the limitations of a surface detector or air fluorescence. In the past year, the Atmospheric Molecular Bremsstrahlung Experimental Radiometer (AMBER) experiment has been searching for isotropic GHz emission from cosmic rays by cross-triggering off of the Pierre Auger Observatory in Argentina. Updates on the AMBER experiment's current status will be presented.

Hunting supersymmetric dark matter in gamma-rays

7/24/12
Zhaoyu Yang (OSU/CCAPP)

Annihilation or decay of dark matter can produce continuum or monoenergetic gamma-rays. Substantial progress has been made in the searches for dark matter through gamma-rays since the launch of the Fermi Gamma-ray Space Telescope. The Fermi-LAT has measured gamma rays with unprecedented accuracy and statistics in the GeV-TeV energy range. The experiment starts to enter the intriguing regions of parameter space where supersymmetric particles could provide dark matter candidates. I will briefly review the extensive searches for gamma-rays from dark matter with the Fermi-LAT and also discuss the complementarity between indirect, direct and collider searches.

A Census of AGN Activity in the Bootes Field

7/24/12
Sun Mi Chung (OSU/Astronomy)

AGN are crucial probes of the accretion history of black holes in the universe and the co-evolution of AGN and galaxies. In order to find statistically meaningful samples of AGN, large surveys are necessary. Typically these surveys have covered a large area in the sky with a relatively bright apparent magnitude limit (I<~21), or have gone very deep (I<~25) but cover only a small region of the sky. The Bootes field, with its deep optical imaging (I<~25) and ~9 square degree field, offers a unique opportunity to study AGN and galaxy evolution from a survey that is both deep and wide. By utilizing the extensive multi-wavelength data in the Bootes field, we are able to construct spectral energy distributions (SEDs) that range from UV to mid-IR wavelengths. We fit the SEDs with existing galaxy and AGN templates and present a novel way to select AGN candidates.

Lithium in the cosmos Logo

Lithium seven and its problem, thirty years later

7/31/12
Fabio Iocco
(Stockholm U.)

In 1982, seminal work showed the puzzling behaviour of Lithium7 in low-metallicity, halo stars of our Galaxy. Those observations did in fact establish the paradigm of a Lithium7 abundance constant in stars spanning three orders of magnitude in metallicity. Since then, this finding has challenged our understanding of Stellar Atmospheres, Cosmological Nucleosynthesis and Stellar Formation environments, becoming known as the "Lithium Problem". Thirty years later, this problem is far from being solved, yet these decades of activity have brought new observations and theoretical advances in the field of cosmology, stellar evolution, stellar atmospheres, cosmic ray and primordial nucleosynthesis, bringing together fields traditionally apart. I will give an overview of the problem in an historical context, and examinate the new progress made by all related fields, as recently discussed in the conference "Lithium in the Cosmos".

Simulating the stacked spectrum of the Lyman alpha forest

8/7/12
Michael Mortonson (OSU/CCAPP)

The large sample of quasar spectra observed in the Sloan Digital Sky Survey has made it possible to study properties of the intergalactic medium along quasar sightlines using a statistical approach that identifies absorption correlated with features in the Lyman alpha forest. Lyman series and metal lines detected in the stacked spectrum provide information about the physical conditions and metal content of relatively low-density gas that is not accessible in individual quasar spectra. Interpreting the features detected in the stacked Lyman alpha forest spectrum requires detailed modeling of the observations using cosmological hydrodynamic simulations. I will present results of a simulated stacking analysis using spectra extracted from a large hydrodynamic simulation at redshift 2.5. The similarities and discrepancies between the simulated and observed stacked spectrum can be used to improve models of metal enrichment used in simulations and to refine the stacking methods applied to data.

Black hole mass estimates:
From the local universe AGN to the highest redshift QSOs

8/7/12
Gisella DeRosa (OSU/Astronomy)

Supermassive black holes (BHs) are thought to play a key role in the evolution of galaxies. Therefore, it is of fundamental importance to properly characterize the masses and accretion rates of BHs through cosmic time. While direct dynamical measurements of BH masses are possible only for nearby quiescent galaxies, reverberation mapping can be used to obtain direct measurements of BH masses powering distant active galactic nuclei. A major result of the RM campaigns is the identification of the relationship between the size of the broad line region and the luminosity of the AGN, which allows to estimate the BH masses from single epoch spectral measurements up to very high redshift. After a brief review of reverberation mapping and single epoch measurements techniques, I will present preliminary results for both AGN in the local universe and a new sample of z~7 QSOs.

Bringing the Stars to Earth: Laboratory Astrophysics at OSU

8/14/12
Chris Orban (OSU/Physics)

Advances in laser technology and other technical achievements have made plasmas at stellar densities and temperatures directly accessible in the lab for the first time, without any appeal to scaling arguments. I will describe several on-going and planned experiments in this category that researchers at OSU are contributing to. In particular, laser experiments at a number of different facilities can potentially resolve discrepancies that have emerged from Iron opacity measurements conducted at the Sandia Z pinch, which may ultimately help resolve long-standing debates over solar abundances. I will end with a brief discussion of the wide variety of laboratory astrophysics experiments being planned for the National Ignition Facility, currently the largest and most energetic laser platform in the world.

Milky Way Disc and Halo

8/14/12
Ralph Schoenrich (OSU/CCAPP/Astronomy)

I will give a short outline of analytic disc modelling and the question of the Galactic thick disc. Further I will show how this modelling affects our knowledge of Galactic parameters and the Solar motion. I will further discuss distance estimates as well as estimators for Galactic rotation and implications for understanding the structure of the Galactic halo.

The public cosmic void catalog

8/16/12
Paul Sutter (OSU/CCAPP)

Cosmic voids are potentially a rich source of information for both astrophysics and cosmology. To enable such science, we produce the most comprehensive void catalog to date using the Sloan Digital Sky Survey Data Release 7 main sample out to redshift z = 0.2 and the Luminous Red Galaxy sample out to z = 0.44. Using a modified version of the parameter-free void finder ZOBOV, we fully take into account the presence of survey boundary and masks. We discuss basic catalog statistics such as number counts and redshift distributions, as well as describe some example data products derived from our catalog, such as radial density profiles and projected density maps.

VHE Excess and Cascade Gamma Rays

8/21/12
Kohta Murase (OSU/CCAPP)

Recent observations of the isotropic diffuse background by Fermi/IceCube allow us to get more insight into distant very-high-energy (VHE) and ultra-high-energy (UHE) gamma-ray/neutrino emitters, including cosmic-ray accelerators/sources. We focus on the contribution of intergalactic cascades induced by gamma-rays and/or cosmic rays (CRs) to the diffuse gamma-ray background (DGB) in view of the latest Fermi data. We identify a possible VHE Excess from the fact that the Fermi data are well above expectations for an attenuated power law, and show that cascades induced by VHE gamma rays (above ~10 TeV) and/or VHECRs (below ~10^19 eV) may significantly contribute to the DGB above ~100 GeV. The relevance of the cascades is also motivated by possible VHE excesses found in TeV blazars such as 1ES 0229+200, which may suggest very hard intrinsic spectra. We discuss their connections and show the importance of future detailed VHE DGB measurements.

Survey-only discovery of the planet in the microlensing event MOA 2011-BLG-028/OGLE-2011-BLG-0203

8/21/12
Jan Skowron (OSU/Astronomy)

I will present the analysis of the Neptun-class planet discovered in the curse of the microlensing event observed by the survey telescopes. MOA Telescope in New Zeleand and OGLE Telescope in Las Campanas, Chile are dedicated microlensing facilities that have recently received upgrades and are now capable of characterizing short-time deviations in the light curves of the microlensing events and, thus, discovering planets in regular survey cadence. The discussed planet is one of the first discovered in that mode. I will give estimates on the mass of the planet, distance from its host and position in the Galaxy.

Anapole Dark Matter / The Life and Times of Gary Steigman

8/24/12
Robert (Bob) Scherrer
(Vanderbilt)

In honor of this momentous occasion, I will give two half-hour talks.
For the first half, I will talk about anapole dark matter. There has been a great deal of recent interest in electromagnetically-interacting dark matter, particularly electric and magnetic dipoles. However, the anapole is the only allowed electromagnetic form factor for Majorana particles, and it has not been as extensively investigated. Anapole dark matter has several interesting differences from electric or magnetic dipole dark matter. It annihilates exclusively into fermions via a purely p-wave interaction, and an interaction strength sufficient to account for the present-day dark matter abundance can be made consistent with direct-detection experiments for dark matter masses in the GeV range; this is not the case for the electric or magnetic dipole.
In the second part of my talk, I will discuss Gary Steigman's contributions to cosmology, and place them in their historical and intellectual context. I will also show some funny pictures of Gary.

The Multiwavelength Structure of a Quasar from Microlensing

8/28/12
Jeffrey Blackburne (OSU/Astronomy)

The gravitationally lensed quasar HE 1104-1805 has been observed at a variety of wavelengths ranging from the mid-infrared to X-ray, over nearly 20 years. The light curves show variability resulting from the microlensing of the quasar by stars in the lens galaxy. We combine data from the literature with new observations from the SMARTS telescope and HST, and use them to investigate the spatial structure of the central regions of the quasar. The wide wavelength coverage allows us to constrain not only the size of the accretion disk, but the power-law slope of the size-wavelength relation. The size is larger than the standard thin disk model predicts by a factor of 3-10, and its variation with wavelength is consistent with the model, but favors smaller values. We put upper limits on the source size in soft and hard X-ray bands, finding that the majority of the light in both bands comes from the innermost ~10 gravitational radii. We also estimate the inclination of the accretion disk (close to face-on) the mean mass of the stars in the foreground lensing galaxy, the direction of the transverse peculiar velocity of the lens, and the position angle of the projected accretion disk's major axis.

AGN Outflows: The Case of Relativistic Outflows in Ark564

8/28/12
Anjali Gupta (OSU/Astronomy)

AGN feedback has been invoked to solve a number of astrophysical problems. Feedback from jets is sufficient to regulate black hole growth in dominant cluster galaxies, but only about 10% of all quasars have powerful radio jets, so jet-related feedback cannot be generic. Outflows are ubiquitous in AGNs, manifested by blue shifted absorption lines in the soft X-ray and UV bands. The outflows could potentially be a more common form of AGN feedback, but in few cases where mass, energy, and momentum outflow rates could be determined, the feedback was found to be several orders of magnitude below what is required by theoretical models. Recently discovered relativistic outflows (with velocities over ~0.1c) would alleviate this problem, making it crucial to understand whether outflows with relativistic velocities are common in AGN. In this talk, I will review the X-ray AGN outflows and present our results on the discovery of relativistic outflows in Ark564.

mapping

The Energy Frontier in Nature: Highest Energy Cosmic Radiation

9/4/12
Guenter Sigl
(DESY)

Cosmic rays have been observed up to several 10^20 eV through the showers of secondary particles they induce in the atmosphere. Their existence poses formidable challenges and exciting prospects at the same time: Their origin and sources have not been identified yet, but they already allow to test physics at center of mass energies unattained in the laboratory, albeit in a rather indirect way. We will give an overview over the current situation, open questions and future prospects, including the role of secondary gamma-rays and neutrinos produced in interactions of charged primary cosmic rays. Possible origins of the two tentative extraterrestrial neutrino detections by IceCube will also be discussed in this context. Part of this will be based on simulation with CRPropa 2.0, our new public multimessenger propagation code.

CMB Lensing Measurements:
Mapping Dark Matter with ACT and ACTPol

9/11/12
Blake Sherwin
(Princeton)

CMB lensing measurements use the cosmic microwave background to map the projected distribution of dark matter out to high redshifts. I will describe the first detection of the CMB lensing power spectrum with the Atacama Cosmology Telescope (ACT) and its cosmological implications, and will show results from cross-correlations of ACT CMB lensing maps with quasars, galaxies and other tracers of dark matter. I will then explain the great scientific potential of upcoming polarization lensing measurements with ACTPol, and will discuss the development of a lensing pipeline for this experiment.

Bayesian hierarchical models for supernovae type Ia cosmology

9/18/12
Roberto Trotta
(Imperial College, London)

Supernovae type Ia (SNIa) are standardazible candles that can be used to determine distances in the Universe and hence to learn about the expansion history of the cosmos, as well as to detect and characterize dark energy. In this talk I will present recent advances in determining distances for SNIa and in inferences on cosmological parameters thanks to Bayesian hierarchical models, that allow one to include in a principled statistical way all sources of uncertainty (measurement error, population-level distributions, dust extinction, etc). I will demonstrate how these new methods outperform the standard approach in the vast majority of cases, leading to significantly improved cosmological constraints and smaller bias.

Constraining Dark Matter and SUSY with global fits including LHC and direct detection data

9/25/12
Charlotte Strege
(Imperial College, London)

Signatures of Beyond the Standard Model Physics, including dark matter, are currently being searched for with several observational channels, such as the LHC and direct detection experiments. These experiments already place constraints on several theoretical WIMP models, including weak-scale supersymmetry (SUSY), and will probe the bulk of this parameter space in the next 5 - 10 years. In this talk, I will present new constraints on the parameters of the constrained Minimal Supersymmetric Standard Model (cMSSM) obtained from global fits including the LHC Higgs discovery, recent data from LHC SUSY searches and the XENON100 direct detection experiment. I will discuss the impact of astrophysics and particle physics uncertainties in interpreting the results from direct detection. I will also present the reach of future ton-scale direct detection experiments and illustrate how statistical fluctuations in the recoil energy spectrum can induce large systematic biases in the WIMP mass reconstruction even in a regime with hundreds of signal events. I will show how target complementarity can reduce - but not eliminate - such uncertainties.

Microwave Detection of Cosmic Ray Air Showers

10/2/12
Christopher Williams
(U. of Chicago)

I will present the design and implementation of the Microwave Detection of Air Showers (MIDAS) experiment, a pathfinder for detection of Extensive Air Showers (EAS) induced by Ultra High Energy Cosmic Rays (UHECRs). The MIDAS experiment uses a multi-pixel imaging telescope instrumented with commercially sourced GHz receivers and custom fast-detection electronics to search for EAS. The microwave detection technique is analogous to the already successful fluorescence technique, but with nearly 100% duty cycle. If successful, the microwave technique will provide an attractive method for instrumenting the extremely large areas required by future UHECR observatories. The first science phase of the MIDAS experiment gathered 61 days of livetime data operating on the University of Chicago campus. I will present the current limits on EAS microwave emission from this data set. The second science phase is underway with installation of the MIDAS detector at the Pierre Auger Observatory in MalargŁe, Argentina. Operating in coincidence with the Auger surface detector will greatly increase the sensitivity of the MIDAS experiment.

sheldon campbell

Clues for Identifying Dark Matter Through Indirect Detection

10/9/12
Sheldon Campbell (OSU/CCAPP)

The indirect, gravitational evidence for dark matter is deep. Understanding the nature of this matter is a major unsolved problem of modern theoretical physics. One viable explanation is that it is a new fundamental particle that was produced during the big bang. In many such theories, annihilating dark matter can successfully account for the correct cosmic density of the dark matter relic that we see. If those theories are true, then colliding dark matter particles are still slowly annihilating today, injecting annihilation products into space. Telescopes today are searching for evidence of this type of signal in high energy gamma-rays, cosmic rays, and neutrinos.
In this talk, I will show examples of how different particle physics properties of dark matter affect the intensity of its annihilation products, particularly the observed mean spectrum, and the angular power spectrum. I focus on gamma-ray and neutrino signals for which there can be contributions both from within the galaxy and from all extragalactic annihilations. I will explain the important aspects of large scale structure that affect the extragalactic signal, and will briefly discuss the uncertainties of large scale structure that could be constrained by the observation of an annihilation signal.

tim arlen

Intergalactic Magnetic Fields and Extreme TeV Blazars

10/11/12
Tim Arlen
(UCLA)

Very High Energy (VHE) gamma-rays (E > 100 GeV) emitted from distant Active Galactic Nuclei interact with the diffuse far-IR to UV extragalactic background light (EBL) in intergalactic space, producing electron positron pairs. These pairs are deflected by the intergalactic magnetic field (IGMF), and in turn, inverse Compton (IC) scatter CMB and EBL photons up to GeV-TeV energies, as delayed secondary emission. For hard spectrum "Extreme" sources, the secondary IC emission thus produced modifies the observed spectrum of the source, and is potentially detectable by IACTs and the Fermi-LAT instrument. We review recent constraints on IGMF which were reported in the literature and derived for 3 TeV-detected blazars-1ES 0229+200, 1ES 1218+304, and RGB J0710+591. Through detailed Monte Carlo simulations, incorporating all major effects of QED and cosmological expansion, we research effects of major uncertainties such as the past history of emission, spectral properties of the source, undersampled IACT coverage, source vs. observer geometry, and AGN jet Doppler factor. The implications of these effects on the recently reported lower limits of the IGMF will be thoroughly examined.

Eric Baxter

Extracting Small Cosmological Signals from Diverse Data Sets

10/16/12
Eric Baxter
(U. of Chicago)

In this talk I will discuss the extraction of cosmologically relevant signals from three very different types of data: gamma-ray maps, 21 cm maps, and temperature maps of the CMB. The gamma-ray sky may contain important information about annihilating dark matter; getting at this information is complicated by the presence of large astrophysical backgrounds. Primordial non-gaussianity can leave an imprint on the bubble distribution during reionization; again, however, we must contend with large foregrounds. Gravitational lensing by galaxy clusters leaves a small imprint on the CMB; extracting this information requires understanding contaminants such as the distortion caused by the Sunyaev-Zel'dovich effect. Despite the apparent differences between these data sets, their analyses share many common features.

Haibo Yu

Exploring Dark Matter From Colliders to the Cosmos

10/24/12
Haibo Yu
(U. of Michigan)

Astrophysical and cosmological observations provide compelling evidence for the existence of dark matter in the Universe, but its particle physics nature remains mysterious. The weakly-interacting massive particle (WIMP) has been proposed as a dark matter candidate. In this talk, I will first show that particle colliders including the Tevatron and the LHC are powerful tools to hunt for WIMP dark matter. I will also discuss dark matter models beyond the WIMP paradigm and search strategies for them. Astrophysical objects such as neutron stars and dwarf galaxies provide natural laboratories for exploring dark matter beyond the WIMP.

Patchy Screening of the Cosmic Microwave Background by Inhomogeneous Reionization

10/24/12
Vera Gluscevic
(Caltech)

In spite of the existence of various observational constraints on the duration of the epoch of cosmic reionization (EoR), very little is yet known about the details of the reionization process. The current paradigm is that it was highly inhomogeneous, with ionized bubbles forming around the first sources of light, expanding, and eventually filling out the entire volume of the intergalactic medium (IGM) by the end of the EoR. Results from radio surveys attempting to map the morphology of the IGM during the EoR, using the redshifted 21-cm signal from atomic hydrogen, are still years in the future. I will discuss an alternative probe: higher-order cross-correlations in temperature and polarization maps of the cosmic microwave background (CMB). I will present current CMB constraints for a simple reionization model whose parameters can be used as figures of merit for future experiments. I will also show forecasts for Planck and an EPIC-like mission, and discuss the implications of the recent results from the EDGES experiment.

How Wrinkles form in the Universe and How to Deal with their Information-Sabotage

10/30/12
Mark Neyrinck
(Johns Hopkins U)

Structures ("wrinkles") in the Universe like filaments and haloes are essential components of the arrangement of matter on large scales. They form in analogy to the origami-folding of a sheet of dark-matter. I will discuss some uses of this Lagrangian viewpoint, for instance an ORIGAMI algorithm that identifies structures in a natural way, finding particle crossings in N-body simulations. While these structures are fascinating, and conveniently allow observers like us to exist, they also make it harder to extract cosmological information on nonlinear scales. In particular, sharp peaks greatly diminish the statistical power of the power spectrum and two-point correlation function, the most widely used statistics in cosmology. In the second part of my talk, I will discuss how to fix these statistics with logarithmic glasses.

The Blazar and Dark Matter Contribution to the Diffuse Gamma-Ray Background

11/9/12
Pat Harding
(Irvine)

The source of the diffuse gamma-ray background (DGRB), as measured by the Fermi Large Area Telescope, has been an unsolved question for some time. I will discuss the relation between the measured anisotropies in the DGRB and the DGRB spectral intensity, and their potential origin from the unresolved blazar population. I will also discuss how characterizing the DGRB provides one of the most conservative constraints on models of annihilating weak-scale dark matter particles.
Using a physical-evolution model for blazars with a luminosity dependent density evolution (LDDE) and an observationally-determined luminosity-dependent blazar spectral energy distribution, I find that blazars can account for the observed anisotropy of the DGRB consistent with their observed source-count distribution, but are in turn constrained in contributing significantly to the observed DGRB intensity. For the best-fit LDDE model accounting for the DGRB anisotropy and source-count distribution, blazars only contribute 6% of the DGRB intensity above 1 GeV. However, this LDDE model finds that greater than 76% of the DGRB anisotropy is due to blazars.
The blazar-dominated DGRB provides a strong limit on any astrophysical contributor to the DGRB flux: any additional population which contributes to the remaining 94% of the DGRB intensity must produce less than 24% of the DGRB anisotropy. In particular, I will discuss the diffuse emission from annihilating dark matter. I will show that the DGRB provides one of the most conservative constraints on models of annihilating weak-scale dark matter particles.

Results of dark matter searches in dwarf galaxies with Fermi

11/13/12
Alex Geringer-Sameth
(Brown)

I will present new results from a search for both continuum and line emission from dark matter annihilation in Milky Way dwarfs. These results are based on the joint analysis of dwarf galaxy data from the Fermi Gamma-ray Space Telescope using a statistically optimal weighting of individual photons including both spatial and spectral information. This new technique, applied to the indirect dark matter search, is strong enough to probe generic WIMP candidates that reproduce the relic abundance. I will discuss the details of the framework and how it may be applied to other situations, including making predictions for future experiments.

Detection of ultra-high energy cosmic neutrinos with the IceCube neutrino observatory and its implications to the origin of ultra-high energy cosmic rays

11/16/12
Shigeru Yoshida
(Chiba U.)

We review the present status of the search for ultra-high energy (UHE) cosmic neutrinos with the IceCube Neutrino Observatory. The IceCube neutrino observatory has currently realized the best sensitivity on detection of cosmic neutrinos in UHE energy range of PeV up to 10EeV (=10^10 GeV), by the standard neutrino detection technique measuring ultra-violet Cherenkov light emissions. The most updated results from the data obtained by the full instrumentation volume of the IceCube optical sensor array are reported. Two neutrino-induced events have been found to pass the final signal search criteria. Their primary neutrino energies are estimated to be beyond 1 PeV, indicating that they are the most energetic neutrinos we have ever seen in the history of neutrino astrophysics. We present their features in some details, followed by discussions on the implication to origin of ultra-high energy cosmic rays.

Anders Pinzke

Gamma-ray emission from clusters of galaxies - a competition between cosmic rays and dark matter

11/20/12
Anders Pinzke
(Santa Barbara)

Clusters of galaxies are expected to be significant gamma-ray emitters with contributions from both annihilating dark matter (DM) and the cosmic-ray (CR) proton induced pions that decay into gamma-rays. Besides establishing an entirely new class of sources, gamma-ray observations of clusters open up a unique window for studying the physics of high energy, non-thermal processes in cosmic large-scale environments. I use a selection of supersymmetric DM models and estimate the gamma-ray flux from various emission processes. To extend these predictions for nearby galaxy clusters, I present a CR model that allows us to reliably predict both the spatial and spectral emission profiles from pion decay and inverse Compton. I identify the brightest clusters for both Fermi-LAT and current imaging air Cherenkov telescopes, and use gamma-ray observations to constrain CR- and cluster-physics as well as the expected boost of annihilating DM from substructures.

Probing Neutrino Oscillations at Very Short Baselines with Reactors and Radioactive Sources

11/21/12
Karsten Heeger
(U. of Wisconsin, Madison)

Data from a variety of neutrino experiments as well as cosmology seem to suggest the existence of additional light, sterile neutrino states. A re-analysis of short-baseline reactor neutrino experiments recently revealed a discrepancy of about 5.7%, or ˜2.5σ, between the measured reactor antineutrino flux and predictions. This reactor anomaly can be interpreted as a sign of new physics, or could be due to uncertainties in the nuclear physics underlying reactor antineutrino flux and spectrum predictions. A new experiment at very short baselines of O(10m) is needed to test the hypothesis of oscillation into sterile neutrinos and to make a precision measurement of the reactor antineutrino spectrum. US research reactors with highly-enriched fuel and compact cores provide a unique opportunity for a definitive reactor experiment at very short-baselines. Alternatively, radioactive antineutrino sources may be used in existing detector facilities. We discuss the experimental prospects for resolving this neutrino anomaly.

dragon stars

The Star Forming Cosmic Gamma-ray Background

11/27/12
Nachiketa Chakraborty
(Illinois)

The origin of the cosmic, diffuse gamma ray background (EGB) is still an open question. Amongst observed astrophysical sources, the most promising candidate sources are star-forming galaxies, active galaxies and potentially others including pulsars. Only after evaluating contributions from these guaranteed sources can one accommodate contributions from exotic sources such as annihilating or decaying dark matter. In the light of detection of resolved star-forming galaxies by Fermi-LAT, their unresolved counterparts constitute an important component of the EGB as measured by LAT. Computation of the total contribution from both normal and starburst galaxies via various mechanisms to the EGB in the LAT energy range shows that the total gamma-ray emission from the star-forming universe could account for a significant fraction of EGB for the best case model. Even less optimistic models remain an important contribution. The most dominant gamma ray production mechanism as established by LAT data analysis is from the hadronic channel involving neutral pion decay. A new calculation of leptonic gamma rays via inverse-Compton (IC) scattering of cosmic ray electrons shows it to be second most important though subdominant to pionic throughout the LAT range. The bremsstrahlung component is further lower. It may be possible to distinguish amongst the EGB candidates with the help of observables such as spectral features, statistics, anisotropy of sources, etc. These advances in our understanding of the origin of the EGB can put strong constraints on fundamental physics and astrophysics.

Weakening gravity at small distances and times

11/30/12
Anupam Mazumdar
(Lancaster UK)

I will discuss an extension of general relativity which may be able to render gravity extremely weak in the deep ultra-violet, while recovering the Newtonian gravitational potential in the far infrared. Such a construction has fundamental consequences the way we think about gravity especially near the black hole geometry and close to the cosmological singularity.

Kepler Mission

Constraining Primordial Black Hole Dark Matter using Microlensing

12/4/12
Agnieszka Cieplak
(UCSD)

Primordial Black Holes (PBHs) remain a Dark Matter (DM) candidate of the Standard Model of Particle Physics. I will present a new method to potentially constrain up to 40% of the remaining PBH DM mass range using microlensing of Kepler source stars. The combination of exceptional photometric precision of the Kepler mission and the increase in cross section due to the large angular sizes of the nearby Kepler stars, allows for the possibility of extending the theoretically detectable PBH DM mass range two orders of magnitude below current limits. I will address how to extract the DM properties such as mass and spatial distribution if PBH microlensing events were detected, and present a new formalism for calculating microlensing rates in the presence of large finite-source limb-darkening effects, correcting a well-known finite-source limb-darkening microlensing formula. Finally, I will present an approximation for estimating the predicted rate of detection for a given star, which will be used for future missions, closing with a preliminary look at the Kepler lightcurve data.

manos

Superluminous Supernovae from Pair Instability and from SN ejecta - Circumstellar Matter Interaction: Insights from Light Curve Fits and Simulations

1/15/13
Manos Chatzopoulos
(U. of Texas, Austin)

Superluminous Supernovae (SLSNe) appear to come in two main spectroscopic flavors: hydrogen-rich (such as SLSN 2006gy, SLSN 2006tf, SLSN 2008am) and hydrogen-poor (such as SLSN 2007bi, SLSN 2008es, SLSN 2010kd). SLSNe are thought to be the result of either violent, massive SN ejecta - circumstellar interaction or massive stars that encounter electron-positron pair instability in their oxygen cores (Pair Instability Supernova; PISNe). In the present work, we use the observed LCs of 9 SLSNe and other objects in which CSM interaction might be relevant and fit a series of SN LC models for different power input mechanisms (radioactive decays of Ni-56 and Co-56, magnetar spin-down, CSM interaction) using a new x2 - minimization code. The analysis of the fitting results and the implied model parameters suggest that CSM interaction is the most likely mechanism for the majority of hydrogen-rich SLSNe. We suggest that hydrogen-poor CSM interaction can also be relevant in hydrogen deficient SLSNe, such as SLSN 2006oz and even SLSN 2007bi as an alternative to the PISN scenario. In addition, we present models of hydrogen-poor CSM shells ejected by Pulsational PISNe corresponding to rapidly rotating progenitors with smaller masses than in the non-rotating case.

SDSS

Galaxy evolution in groups and clusters in a hierarchical Universe

1/22/13
Andrew Wetzel
(Yale)

Satellite galaxies in groups and clusters play a critical role in the picture of galaxy evolution. As many as a third of all galaxies are satellites, and the quenching of star formation in satellites is the dominant process in building the red-sequence galaxy population at low mass. Furthermore, satellite quenching, and thus color transformation, governs the optical properties of galaxy clusters. I will present an observational and theoretical investigation into the evolution of star formation (and thus color) in satellite galaxies, using the Sloan Digital Sky Survey to examine satellites across a wide range of host halo masses, from massive clusters to the lowest mass dwarf galaxy groups in the local Universe. I will place these results in a fully cosmological context using a high-resolution simulation to track satellite orbits and infall times, showing that the star formation histories of satellites follow a delayed-then-rapid quenching (color transformation) scenario. I also will examine the curious evolution of satellites that orbit beyond the virial radius of their host halo.

elise jennings

Detecting modified gravity with improved models of redshift space distortions

1/29/13
Elise Jennings
Chicago/KICP

Forthcoming galaxy spectroscopic surveys will make high precision measurements of the clustering of galaxies on scales in excess of 100 Mpc/h. In particular, the distortion of clustering due to the peculiar motions of galaxies and the apparent scale of characteristic features in the galaxy distribution have been proposed as tests of the cosmic acceleration. To obtain meaningful and robust constraints on dark energy, we need to understand any systematics in these measurements. I will present the predictions for redshift space distortions from large volume and high resolution N-body simulations and discuss the accuracy of current models in recovering the growth rate. I will present predictions of the clustering of dark matter in redshift space in f(R) modified gravity and in quintessence dark energy cosmologies. Due to the size and resolution of these simulations, this is the first time that the nonlinear matter and velocity fields in this class of modified gravity models has been resolved to a high level of accuracy over a broad range of scales.

High precision cosmology with large-scale structure

2/6/13
Hee-Jong Seo
(BCCP, LBL/Berkeley)

Baryon acoustic oscillations (BAO) in large-scale structure provide an excellent standard ruler test to measure the cosmological distance scales (such as the angular diameter distance and the Hubble parameter), and therefore to probe dark energy properties. In this talk, I will discuss various aspects of BAO surveys, recent high-precision BOSS BAO measurements, and how reconstruction of BAO and other techiniques can be used to recapture cosmological information lost due to nonlinear evolution of structure.

The Interstellar Medium of Galaxies in the Epoch of Reionization

2/12/13
Joseph Munoz
(UCLA)

The ISM of z>~6 galaxies is a crucial element for understanding many important probes of cosmic reionization, such as recently discovered Lyman-break systems in the UDF, the evolution of Lyman-alpha emitters, Swift gamma ray bursts, and intensity mapping of galactic emission lines with ALMA, which can improve the reliability of 21cm tomography. I will present a new, fully-analytic framework for describing the ISM and molecular cloud properties of reionization epoch galaxies that includes physical processes from an enormous range of distance scales---from the tens of megaparsec regions over which cosmic variance operates to the tens of parsec-sized photo-dissociative regions inside molecular clouds---a span typically beyond the reach of numerical simulations. I will discuss the observational consequences of such a model, in particular, examining whether recent Chandra data can constrain the way gas is transported through the disk and making realistic predictions for detecting carbon emission lines with the JVLA and ALMA.

plot of research

Dark Matter Physics:
New Clues from Dwarf Galaxies?

2/19/13
Jesus Zavala Franco
(Waterloo)

The observed abundance and inner densities of dwarf galaxies have been enduring challenges for the otherwise-remarkably successful Cold Dark Matter (CDM) paradigm. They may put to the test two of the fundamental hypothesis underlying this paradigm: dark matter particles are collisionless and have low primordial thermal velocities. In this talk I will review the current status of these challenges and describe how Warm Dark Matter (WDM) and Self-Interacting Dark Matter (SIDM) models are viable alternatives to alleviate these problems, arguing that it is timely to study them as seriously as CDM in the context of galaxy formation.

Cosmic velocity flows in the Local Universe: methods, observations

2/26/13
Guilhem Lavaux
(Waterloo)

A valuable source of information on the distribution of dark matter and the growth of structures lies in the peculiar velocity field of the galaxies. After a short review on techniques available for their determination, I will present the results obtained on two recent techniques that I developed for estimating the large scale cosmic flows. These two techniques are based either on dynamical modeling of galaxy redshift catalog, or the detection of the kinetic Sunyaev-Zel'dovich signal in the Cosmic Microwave Background. I will show the results obtained when they are applied on the recent galaxy surveys and WMAP7 sky maps and some forecasts for PLANCK.

galaxy

A New Probe of Dark Matter in Spiral Galaxies

3/12/13
Sukanya Chakrabarti
(Rochester Institute of Technology)

The cold dark matter paradigm of structure formation is successful at recovering the basic skeletal structure of the universe -- the large-scale distribution of galaxies. However, agreement between theory and observation is less secure when this model is applied to galactic (and sub-galactic) scales. The "missing satellites problem" and discrepancies between the observed structure of dwarf galaxies and simulations have prompted us to develop an inverse method of characterizing galactic satellites. The extended atomic hydrogen disks of galaxies are ideal tracers of tidal interactions with satellites and the galactic gravitational potential well. Our "Tidal Analysis" method allows us to infer the mass, and relative position (in radius and azimuth) of satellites from analysis of observed disturbances in outer gas disks, without requiring knowledge of their optical light. I will present the proof of principle of this method by applying it to galaxies with known optical companions. I will also present our earlier prediction for a dim and yet undiscovered companion of the Milky Way. I will end by presenting preliminary work on the application of this method to characterize the density profile of the dark matter halo in spiral galaxies.

darkmatter

Simulations of Lyman-Alpha Forest with Nyx

3/26/13
Zarija Lukic
(LBL)

Measurements of the Lyman-alpha (Ly-a) forest in spectra of distant quasars open an additional avenue for probing cosmological parameters and the nature of cosmic expansion. The forest is particularly appealing as it probes higher redshifts than most other methods, z~2-4, but also because the signal comes from sampling lower densities of the cosmic web, with different systematic errors from probes tracing galaxies or galaxy clusters. On large-scales, the Ly-a power-spectrum is used as a standard ruler, measuring the BAO scale at high redshifts. On small-scales (the high-end of the power spectrum), the Ly-a forest allows one to constrain neutrino masses, and offers the promise of distinguishing between modified gravity and dynamical dark energy models. As a part of DOE's SciDAC-3 program, we have developed a new AMR hydro + N-body code called Nyx, with the primary goal of producing accurate predictions for the Ly-a forest under different cosmological models and UV background histories. In this talk I will present details of the code, show results from our first Ly-a simulations, and outline our future simulation campaign.

water purification system

The Earth's composition study using neutrino oscillation

3/28/13
Akimichi Taketa
(Earthquake Research Inst, U of Tokyo)

The neutrino oscillation is sensitive to the electron density. On the other hand, the neutrino absorption is sensitive to the nucleus density, i.e., mass density. If we know precise mass density from neutrino absorption or some Earth models, we will be able to measure the A/Z ratio deep inside the Earth and to study about the Earth's core/mantle composition using neutrino oscillation. In this talk, I will discuss about this geophysical potential of new generation neutrino detectors, PINGU and Hyper-Kamiokande.

charting

Few-body physics in the first few minutes:
Physics of light nuclei in the big bang

3/29/13
Kenneth Nollett
(Ohio University)

The earliest time in the history of the universe that is clearly probed by observations is the period from about one second to about fifteen minutes after the big bang, when the initial chemical composition of the universe was determined in big-bang nucleosynthesis (BBN). This was a much simpler time than today, so the physical processes that produced measureable amounts of only hydrogen, deuterium, helium, and lithium can be easily modeled. By comparing the isotopic compositions of these elements againts the model, we learn about the structure and contents of the universe. The light nuclei involved in BBN are interesting in their own right; theorists have only recently produced predictive models of how properties of light nuclei arise from those of neutrons and protons. I will discuss the use of BBN as a cosmological probe, emphasizing the connections between recent applications of the model and recent developments in the physics of light nuclei.

Bayesian Large scale structure

Large Scale Bayesian Inference in Cosmology

4/2/13
Jens Jasche
(IAP)

Already the last decade has witnessed unprecedented progress in the collection of cosmological data. Presently proposed and designed future cosmological probes and surveys permit us to anticipate the upcoming avalanche of cosmological information during the next decades. The increase of valuable observations needs to be accompanied with the development of efficient and accurate information processing technology in order to analyse and interpret this data. In particular, cosmography projects, aiming at studying the origin and inhomogeneous evolution of the Universe, involve high dimensional inference methods. For example, 3d cosmological density and velocity field inference requires to explore on the order of 107 or more parameters. Consequently, such projects critically rely on state-of-the-art information processing techniques and, nevertheless, are often on the verge of numerical feasibility with present day computational resources. For this reason, in this talk I will address the problem of high dimensional Bayesian inference from cosmological data sets, subject to a variety of statistical and systematic uncertainties. In particular, I will focus on the discussion of selected Markov Chain Monte Carlo techniques, permitting to efficiently solve inference problems with on the order of 107 parameters. Furthermore, these methods will be exemplified in various cosmological applications, raging from 3d non-linear density and photometric redshift inference to 4d physical state inference. These techniques permit us to exploit cosmologically relevant information from observations to unprecedented detail and hence will significantly contribute to the era of precision cosmology.

Three-Dimensional Simulations of Core-Collapse Supernovae

4/16/13
Sean Couch
(Chicago)

Core-collapse supernovae (CCSNe) are the luminous explosions that herald the death of massive stars. Neutron stars, pulsars, magnetars, and stellar-mass black holes are all born out of these explosions. Some Gamma-Ray Bursts (GRBs) have been associated with CCSNe, raising the possibility of a common progenitor for both. CCSNe are chiefly responsible for the production of elements heavier than iron throughout the universe; their importance in galactic chemical evolution cannot be underestimated. The first stars, expected to be relatively massive, likely ended as CCSNe as well. These bright events, occurring just a couple million years after the Big Bang, may be some of the most distant, observable objects in the universe with the upcoming James Webb Space Telescope. Despite the importance of CCSNe to our understanding of many aspects of the universe the mechanism that reverses stellar core collapse and drives supernova explosions is not fully understood. The CCSN mechanism is one of the most important challenges for modern computational astrophysics. I will discuss the current state-of-the-art of CCSN theory and simulation, with an emphasis on my recent work on three-dimensional CCSN simulations. I will highlight some of the most interesting and important questions supernova theorists are currently wrestling with, in particular the importance of fully three-dimensional simulations.

NASA NuSTAR images

Focusing Hard X-rays with NuSTAR: First Results from Multi-epoch Observations of the Bullet Cluster and NGC 253

4/22/13
Daniel Wik
(NASA Goddard)

NuSTAR is the first satellite capable of focusing hard (>10 keV) X-rays, increasing our sensitivity to point sources 100-fold and spatially resolving arcminute-scale objects for the first time. In this talk, I will briefly introduce the mission, its primary science goals, and a few early results from the various science working groups. I will then focus in depth on our observations of the massive, merging "Bullet" galaxy cluster and the nearby starburst galaxy NGC 253. In particular, the temperature structure of the Bullet cluster and early Chandra/NuSTAR joint spectroscopy of bright X-ray binary sources in NGC 253, along with prospects for interesting limits on diffuse inverse Compton emission from both, will be presented.

plot

Searches for Low-mass WIMPs with CDMS II and SuperCDMS

4/23/13
Richard Schnee
(Syracuse)

The Cryogenic Dark Matter Search experiment (CDMS II) was designed to directly detect WIMP dark matter by simultaneously measuring phonon and ionization signals caused by particle interactions in semiconductor targets, allowing event-by-event discrimination of signal from background via the relative sizes of the two signals. Data from the CoGeNT, CRESST II, and DAMA/LIBRA experiments have hinted at a low-mass WIMP signal. I will review these results and the (similarly sensitive) analyses performed by the CDMS II collaboration. Most recently, three WIMP candidate events were observed in a blind analysis of data from eight CDMS II Si detectors with an expected background <1 event. I will also describe the prospects for future searches at low mass with the SuperCDMS dark-matter program, including searches with the new interleaved detectors currently taking WIMP-search data in the Soudan Mine (with energy thresholds ~5x lower than previous detectors), as well as the long-term expected sensitivity of the SuperCDMS technology.

Lindley Winslow with quantum dots.

Next Generation Scintillation Detectors: Neutrinos and Nanotechnology

05/14/13
Lindley Winslow
(UCLA)

The last decade has seen a revolution in our understanding of the most mysterious of the Standard Model particles, the neutrino, and this last year has been no exception. In the last year, we have seen exciting results from both double beta decay experiments and experiments measuring the last mixing angle θ13. For the most part, the detectors responsible for these measurements use Cerenkov and scintillation light to detect neutrino interactions. The wavelength of this light is matched to the peak efficiency of photo-multiplier tubes. This technique has been finely tuned over the last decades, but no great leaps forward in efficiency have been achieved. Nanotechnology may hold the key to improving both scintillators and photo-detectors. In this talk, I will focus on one particular technology, semiconducting nanocrystals known as quantum dots, and their unique optical properties. I will discuss how their use could enhance the capabilities of new photo-detection technology, and address the needs of the next-generation neutrino experiments.

Lindley Winslow with quantum dots.

Precision physics with PINGU at the South Pole

05/21/13
Carsten Rott
(OSU)

The Precision IceCube Next Generation Upgrade (PINGU) is proposed as a new in-fill array for IceCube at the South Pole, Antarctica. The primary physics goal for PINGU is a determination of whether the neutrino mass hierarchy is normal or inverted using atmospheric neutrinos as the neutrino source. The determination of the mass hierarchy is one of the last unmeasured fundamental parameters in the neutrino sector. PINGU will also have an essential role in the search for low-mass dark matter and might enable us to probe the Earth interior by exploiting matter effects in neutrino oscillations. I will summarize the status of PINGU and present high-lights of on-going sensitivity studies.

Lindley Winslow with quantum dots.

Search for Spectral Lines with the Fermi Large Area Telescope

05/21/13
Andrea Albert
(OSU)

Recently a narrow spectral feature has been reported at 130 GeV localized in the Galactic Center. A gamma-ray spectral line is often considered a "smoking gun" for WIMP annihilations, so this would be a remarkable discovery if confirmed. However, the Fermi LAT Collaboration has searched for spectral lines from 5 to 300 GeV in 5 regions of interest and found no statistically significant (>3 sigma global significance) spectral lines. I will discuss what our search finds near 130 GeV and some of the systematic uncertainties we investigated that may induce false line-like features in our measured energy spectrum.

How Galaxy Physics Can Help Us Understand Weak Lensing

5/28/13
Eric Huff

While weak lensing measurements can provide a useful probe of galaxy-scale physics, it is not commonly appreciated that an understanding of galaxy-scale physics can in turn be used to dramatically improve weak lensing measurements. I will explain how galaxy scaling relations can enhance the weak lensing signal, and show recent results from a lensing magnification measurement using data from the Sloan Digital Sky Survey. The combination of magnification and shear measurements enabled by these techniques will permit significantly better weak lensing constraints on the distribution of mass on galaxy scales, in time for the newest generation of large, high-precision imaging surveys such as the Dark Energy Survey.

High Energy Neutrinos in IceCube

5/28/13
Ranjan Laha

Neutrino astronomy has long promised to reveal the astrophysical sites of particle acceleration and the nature of cosmic rays. With the completion of IceCube, this promise has turned into a reality. In this talk, I will first talk about the neutrino detection techniques in IceCube. I will then concentrate on the recently detected PeV events in IceCube. I will discuss the possible source spectrum and will then show how to robustly distinguish between the source spectrum in future.

Radio Detection of Ultrahigh Energy Neutrinos with ARA

6/4/13
Carl Pfendner

The Askaryan Radio Array (ARA) is an ultra-high energy (UHE) cosmic neutrino detector located at the South Pole. The cosmic ray flux cut off above primary energies of 10^19.5 eV leads us to expect a UHE neutrino flux due to the Greisen-Zatsepin-Kuzmin (GZK) effect. The detection of these UHE cosmic neutrinos will add to the understanding of the sources and physics of UHE cosmic rays. The radio Cherenkov technique is the most promising technique for a long term program to investigate the UHE cosmic neutrino flux. ARA uses this radio Cherenkov technique with radio frequency antennas deployed at a depth of 200m in the Antarctic ice. A prototype ARA TestBed station was deployed in the 2010-2011 season and the first three ARA stations were deployed in the 2011-2012 and 2012-2013 seasons. I will present preliminary results of the first neutrino search with ARA, using data taken from 2011-2012 with the ARA TestBed and describe the techniques that will be applied to data from the subsequently installed stations.

Probing the Anisotropy of the Milky Way Warm-Hot Gaseous Halo

6/4/13
Anjali Gupta

We have known for a while that our Milky Way, like other nearby galaxies, is missing most of its baryons and models of galaxy formation predict that they should reside in the circumgalactic medium (CGM), at warm-hot temperatures. This warm-hot gas in the CGM of the Milky Way is best characterized with absorption and emission studies at soft X-ray energies. Recently, we found that there is a huge reservoir of ionized gas around the Milky Way, with a mass of over 2 billion solar masses and a radius of over 100 kpc. This is an exciting new discovery, but it has its own caveats. We had assumed an average, but constant value of the emission measure for all the sight-lines. By comparing absorption and emission measurements from adjacent fields I will show that the warm-hot gas in the CGM of the Milky Way is not distributed uniformly. I will discuss the anisotropy of the Milky Way warm-hot halo and its effect on the contribution to the missing baryon problem.

Probing the Warm-Hot Intergalactic Medium using Weak, Distributed Metal Absorption -- Early Stages of the project

6/11/13
Stephan Frank

The incomplete census of baryons in the low-redshift Universe is one of the outstanding problems of modern cosmology. Up to 50% of baryons are as yet unaccounted for. It is thought that the primary reservoir of missing baryons is the warm-hot intergalactic medium (or WHIM). This gas is thought to be at temperatures 5 < log T(K) < 7 mainly due to shock-heating during gravitational collapse. Metal ionization species are an ideal probe of these physical conditions. They may be seen via absorption in UV spectra of quasars.

Surveys are underway to search for these metals by identifying individual absorption lines in COS spectra. We propose to measure the signal of weak, distributed absorption between these lines. In doing so, we expect to probe an equally large portion of the baryon budget as found by these surveys. We intend to achieve this by use of searches for correlated absorption that we have refined ourselves.

Probabilistic Image Reconstruction with Radio Interferometers

6/11/13
Paul Sutter

The next generation of radio interferometers will image a wide variety of astrophysical and cosmological sources, delivering an incredible amount of raw data in the process. To enable effective science, we must deconvolve the noisy, incomplete data in a robust, data-driven, and efficient way. In addition, to perform quantitative analysis, we must have methods which deliver uncertainty information about the final processed images. Gibbs sampling, a technique widely used in CMB analysis, can potentially meet all these needs. This Bayesian method is scalable and flexible, requires minimal priors, and provides complete posterior information. We show several examples of using Gibbs sampling to reconstruct simulated images in realistic scenarios and compare Gibbs sampling to traditional deconvolution approaches.

Recent Results from IceCube

6/12/13
Albrecht Karle
(University of Wisconsin)

The IceCube neutrino detector, with 1 Gton of instrumented volume the largest neutrino detector ever built, was completed in December 2010. Today, 3 years of data have been recorded with the almost final and final configurations of IceCube. The very intriguing observation of two events at ~1 PeV energy reported in 2012 was followed up with a targeted search at lower energies. The collaboration recently reported new results with an additional 26 events in the energy range from around 50 TeV to PeV from data taken in the same period. The results form evidence for the presence of astrophysical neutrinos events in the sample. I will discuss the recent results of IceCube and will put these findings and in perspective to various searches for high energy neutrinos with IceCube.

The All Sky Automated Survey for Supernovae

6/18/13
Ben Shappee
(OSU)

The All Sky Automated Survey for Supernovae (ASAS-SN or "Assassin") is a long-term project to monitor the whole sky to find nearby supernovae (SNe) with a global network of fully-robotic telescopes. Many distant SNe observed by volume-limited surveys, including some of the most interesting events, are seen to occur in the outskirts of galaxies or in dwarf galaxies. Locally, most of these SNe are currently being missed by amateurs and galaxy-targeted SN surveys, but could be detected by an all-sky survey. The north ASAS-SN unit, Brutus, recently finished commissioning and is located on Mount Haleakala on Maui, Hawaii. Brutus is equipped with two telescopes on a common mount. Each telescope has a 14cm lens, a large 4.47◊4.47 square-degree field-of-view, and a limiting V-band magnitude of 17.5 allowing us to survey the sky every 3-5 days. Since April of this year Brutus has lead to 8 ATELs, 16 bright CV discoveries, 1 "changing look" AGN, and the discovery of a Type Ia Supernova near maximum-light.

Hot Chromospheres on Ultracool Dwarfs

6/18/13
Sarah Schmidt
(OSU)

Despite having very cool atmospheres, Ultracool Dwarfs show evidence of chromospheric emission, generated by the interaction of magnetic fields with ionized material in their atmospheres. I investigate chromosphres on Ultracool Dwarfs using the presence and strength of the H-alpha emission line from SDSS spectra. Using one-dimensional atmosphere models, I place constraints on the chromospheric temperature structures and filling factors needed to produce the observed H-alpha emission strength. While chromosphreic activity is more common on early-L dwarfs than late-M dwarfs, the chromospheres of early-L dwarfs are much cooler and less extended than those of late-M dwarfs.

Microlensing Planet Discovered Using Data From One Telescope

6/25/13
Radek Poleski
(OSU)

Almost all the microlensing planets discovered so far relied on data collected by different groups and analyzed jointly. The growing capabilities of survey groups, which discover microlensing events, allows finding the planets using survey-only data. I present the analysis of one such case. Data from the OGLE telescope allowed not only detecting the planet but also measuring the second order effects. The measured microlensing parallax places the stellar mass at M/K dwarf boundary. The planet turns out to be a super-Jupiter orbiting the star beyond a snow line, i.e. the third such planet around low-mass star.

Exploring exoplanetary systems beyond 1AU with WFIRST

7/2/13
Matthew Penny
(OSU)

WFIRST (the Wide Field InfraRed Survey Telescope) will be NASA's next flagship astrophysics mission after JWST. Its primary instrument will be a large-format high-resolution near-infrared imager and slitless spectrometer. A primary goal of WFIRST will be to perform a high-cadence microlensing survey of the Galactic bulge to search for low-mass exoplanets beyond the ice line. This poster highlights some of the expected results of the WFIRST exoplanet survey. For example, at Earth-mass, the survey will probe the abundance of planets from less than 1 AU outwards, including free-floating planets. In its peak sensitivity range of ~2-5 AU, WFIRST will be sensitive to planets with masses lower than Mercury. Overall, WFIRST is expected to detect several thousand bound planets, as well as several thousand free-floating planets.

Resolving small scale Dark Matter structures using Indirect Dark Matter Detection

7/2/13
Kenny Ng
(OSU)

Dark matter annihilations from cosmological dark matter halos contribute to the Isotropic Gamma-Ray Background (IGRB) measured by the Fermi Gamma-ray Telescope. The expected gamma-ray intensity depends on both particle physics and astrophysics. Particle physics determines the annihilation rate given the density environment of dark matter, while the astrophysics determines the density distribution of dark matter in the universe. Comparing the IGRB to the gamma-ray observations from the Galactic Center may help to disentangle the particle physics and the astrophysics, as well as shedding light on some tantalizing dark matter annihilation signals.

2012 Reverberation Mapping Campaign

7/9/13
Gisella DeRosa

I will present results from our latest reverberation mapping program, carried out over January-April 2012. During the 120 days of the campaign, we collected both spectroscopic and photometric data for nine Seyfert 1 galaxies from various observatories. We have obtained high sampling-rate light curves of the Hbeta emission line and of the AGN continuum at 5100 Ang for seven AGNs: NGC 3227, NGC 3516, NGC 4151, NGC 5548, Mrk 374, Mrk 478, Mrk 704. I will discuss the analysis of the light curves and the derived time lags between continuum and line emission variation as well as the estimated black hole masses.

Counting Hydrogen and Oxygen Atoms for Metallicities

7/9/13
Kevin Croxall

The metal content of nearby galaxies can be determined in in multiple ways. However these methods require different assumptions, which may or may not be valid, and measurements, not all of which are easily obtained. Consequently, the calibration of abundances in nearby galaxies remains uncertain. I will review current methods of determine the metallicity of HII regions and discuss efforts to significantly constrain the calibration of these scales.

The First Moments of Stellar Death

7/10/13
Tony Piro
(Caltech)

Wide-field, high cadence surveys are allowing us to catch supernovae earlier than ever, often days if not hours after the they first begin. Theoretical work focusing on this early phase of stellar explosions is critical for (1) deriving constraints from observations, (2) predicting and interpreting new discoveries, and (3) helping guide the strategies of future observational efforts. I will discuss theoretical research in each of these areas, including showing how we are beginning to directly measure the properties of stars before they die and investigating how we may potentially observe the elusive events that mark black hole formation.

Dark Matter Searches with the Gamma-ray Anisotropy

7/16/13
Sheldon Campbell

Astrophysical gamma-ray experiments are characterizing the gamma-ray sky. Wide-angle experiments like the Fermi-LAT are especially suited for measuring the angular power spectrum. Since the dark matter distribution is predicted to have a different angular distribution in the sky than other astrophysical gamma-ray sources, the angular signature is sensitive to photon production from dark matter annihilation. In this talk, I will discuss the sensitivity of the gamma-ray angular power spectrum to dark matter annihilations, present some dark matter constraints based on the published experimental measurements, and compare these constraints to the more traditional dark matter searches.

Near-Infrared DIBs in the SDSS-III APOGEE Survey

7/16/13
Gail Zasowski

APOGEE is an ongoing, near-IR, high resolution spectroscopic survey of 100,000 giant stars in the Milky Way's bulge, disk, and halo, which probes both low- and high-reddening environments and is providing us with a unique, homogeneous view of the Milky Way. This dataset is also well-suited to a search for interstellar absorption lines. Recently, Geballe et al. (2011, Nature) reported the first detection of diffuse interstellar bands (DIBs) at wavelengths longer than 1.5 microns along a few lines of sight. Our analysis of the APOGEE spectra has resulted in the detection of such near-IR DIBs along several thousand sight-lines, thus increasing the number of detections in this regime by more than two orders of magnitude. After describing our detection method, I will present correlations between these DIBs and other ISM tracers in both abundance and kinematics, which give us new insights into the environment and properties of these absorption features.

Evidence for High-Energy Astrophysical Neutrinos at IceCube

7/19/13
Dr. Nathan Whitehorn
(University of Wisconsin, Madison)

The origin of high-energy cosmic rays is one of the most persistent mysteries in physics. Neutrinos, as neutral tracers of hadronic acceleration, may offer a new and unique window into this problem and others in high-energy astrophysics. I will discuss recent results from the antarctic IceCube neutrino observatory, the first operating gigaton-scale neutrino detector, showing first evidence for a population of extremely high energy neutrinos (100+ TeV) that cannot easily be explained by processes occurring in cosmic ray showers in the Earth's atmosphere and may be the first evidence for a population of high-energy neutrinos of extraterrestrial origin.

charting

Can we do lensing with DECam?

7/23/13
Peter Melchior

DECam, the newly build camera of The Dark Energy Survey, has seen first light in September 2012 and has, since then, gone through an intense phase of Science Verification, which provides us with crucial information to understand and improve the telescope performance for the survey start in late summer 2013. During this phase, we observed five galaxy cluster fields to study the photometry and lensing performance of the new instrument, seeking to utilize its remarkable Field-of-View of more than 3 square degrees to probe massive clusters and their environment. I will present the first weak lensing results of the DES, and discuss several - partially unsolved - issues that hamper the analysis.

Ultra-High Energy Cosmic Rays: Nuclear Mass Composition and Atmospheric Interactions

7/30/13
James Stapleton

The charge and atomic number of Ultra-High Energy Cosmic Ray (UHECR) nuclei (E>10^18 eV) cannot be directly measured. Astrophysical constraints reduce the set of possibilities to stable atomic nuclei (with 1<=A<=56), but limitations in our understanding of atmospheric cascades confound most attempts to clearly identify UHECR nuclear masses. Determination of these masses would yield important information about their sources (which are still not understood) and their interactions with the extragalactic background light and cosmic microwave background during their transit through extragalactic space. I will present an attempt to further constrain UHECR composition using Xmax (the cascade's penetration depth into the atmosphere) using data from the Pierre Auger Observatory. We construct a linear transformation which computes mass distribution moments from Xmax distribution moments. While this utilizes atmospheric cascade simulations, we show how to reduce the impact of uncertainties in these simulations. This is done by relating the Xmax distribution's skewness to statistical fluctuations in early cascade interactions.

J-PAS: The Javalambre-Physics of the Accelerated Universe Astrophysical Survey

8/6/13
Txitxo Benitez
(Instituto de Astrofisica de Andalucia)

The Javalambre-Physics of the Accelerated Universe Astrophysical Survey (J-PAS) is a very wide field Cosmological Survey to be carried out from the Javalambre Observatory in Spain with a purpose-built, dedicated 2.5m telescope, using a set of 54 narrow band and 5 broad band filters over a 1.2Gpix, 4.7deg2 camera. Starting in 2015, J-PAS will image 8500deg2 of Northern Sky and obtain 0.003(1 + z) precision photometric redshifts for 9 x 107 galaxies, about 50 times more than the largest current spectroscopic survey, sampling an effective volume of ? 14 Gpc3. In addition J-PAS will also carry out a SNIe survey, a cosmic shear survey (thanks to the superb seeing at Javalambre) and a cluster survey, exploring the four main Dark Energy probes. In fact, and thanks to its innovative design, J-PAS will be the first experiment capable of reaching Stage IV according to the Dark Energy Task Force classification, several years before other projects like Euclid or LSST start their operations. The instrumental development of this project involves a small fraction of the cost and complexity of a high multiplexing spectrograph, yet it will produce data which enable a much wider range of Astrophysical applications: J-PAS effectively uses a 4.7deg2 "IFU" which will produce a low resolution 3D image of the Extragalactic Northern sky. Our survey will have a lasting legacy value, serving as a fundamental dataset for future cosmological projects.

A Multi-wavelength Approach to AGN Selection using UV to Mid-infrared SEDs

8/13/13
Sun Mi Chung

Extragalactic surveys have traditionally been either wide and shallow, or narrow and deep. Wide/shallow surveys such as the SDSS and the 2DF Galaxy Redshift Survey allow us to study large populations of both galaxies and luminous AGN, while narrow/deep surveys such as COSMOS and DEEP2 can probe fainter populations. However, the relative rarity of AGN makes it difficult to fully characterize AGN in deep fields or to account for faint AGN in shallow fields. The NOAO Deep Wide-Field Survey (NDWFS) in the 9 square degree Bootes field allows us to explore a cosmologically significant volume with data that is both deep and extensive in wavelength coverage. Utilizing 17 bands of data from the ultraviolet to the mid-infrared, we fit galaxy, AGN, stellar, and brown dwarf templates to the spectral energy distributions of ~800000 sources. By fitting these templates to the data we are able to cleanly separate galactic from extragalactic sources for most of the sample. We also compare the SED fits for a galaxy-only model and a galaxy+AGN model and confirm that SED fitting can be successfully used as a method for identifying large populations of AGN, including extended AGN with significant contributions from the underlying host galaxies.

Applications of Lensed Quasars' Variability

8/13/13
Ana Mosquera
(OSU)

Flux variability of lensed quasars can be used as a fun and fancy way to study the structure of galaxies and quasar accretion disks. These fluctuations are a combination of the intrinsic variability of the quasar, from which it is possible to measure time delays and determine the dark matter halo structure of the lens galaxy, and microlensing variability induced by the stars and compact objects in the lensing galaxy, from which we can measure accretion disk sizes, the mean mass of the stars in the lens galaxy, and the dark matter mass fraction near the lensed images. In my talk I will discuss where these cool measurements are leading us, and the current status of our target selection and follow up.

Cosmological imprints in the intrinsic alignments of Luminous Red Galaxies

8/20/13
Elisa Chisari
(Princeton)

The tidal alignment model has been shown to reproduce the intrinsic alignments of Luminous Red Galaxies on large scales. While intrinsic alignments are usually thought of as a contaminant of cosmic shear measurements, they encode cosmological information and information about the formation history of galaxies. In this talk, I will discuss prospects of using the intrinsic alignments of Luminous Red Galaxies as a probe of baryon acoustic oscillations and primordial non-gaussianity with ongoing and upcoming surveys.

The large-scale structure of the Universe as seen by Planck.

8/27/13
Aurelien Benoit-Levy
(University College London)

One of main results of the 2013 data release of the Planck Collaboration is the first full-sky reconstruction of the lensing potential. The lensing potential is the projection on the sky of all the matter density fluctuations from today up to the last scattering surface and therefore constitutes the most complete information on the matter distribution at high redshift. In this talk, I will explain how the lensing potential, a quantity related to the large-scale structure of the Universe, can be reconstructed from observations of the anisotropies of temperature of the Cosmic Microwave Background (CMB) using the Planck data. I will then present in details the Planck lensing map and describe its use for cosmological studies, from improved constraints on cosmological parameters to joint analysis with current and future large-scale structure surveys.

red galaxies

Probing Dark Matter on Small Scales with Weak Lensing

9/3/13
Matthew George
(UC Berkeley)

The mass profile of galaxies and clusters on small scales is important to a wide variety of problems in astrophysics and cosmology. Gas cooling and stellar feedback directly impact the dark matter distribution, and uncertainty in the stellar initial mass function makes it difficult to separate baryonic and dark components. The abundance of substructure and the inner halo slope are also sensitive to dark matter self-interactions. Uncertainties in these effects will hinder gravitational lensing experiments aiming to constrain dark energy with cluster masses and cosmic shear. I will discuss challenges and opportunities for addressing these issues with weak lensing on small scales. In particular, I will discuss results from a study of halo miscentering with a galaxy group catalog, and forecasts for combining shear and magnification with dynamical masses from current and future surveys. I will also present a novel technique that uses kinematic information from background sources to infer their intrinsic shapes, greatly improving the lensing signal-to-noise per galaxy and enabling weak lensing measurements from individual galaxies.

Possible Signatures of Exotic Dark Matter in Stars

9/10/13
Andrew Zentner
(PITT PACC)

There has been a long-standing quest to identify the dark matter. Numerous recent developments, including recent recent results from dark matter direct detection experiments and indirect searches for dark matter by the Fermi Gamma-ray Space Telescope (FGST), have spurred interest in exotic models of dark matter. First, I will discuss Asymmetric Dark Matter. A possible candidate for the low-mass (< 20 GeV) dark matter that would be consistent with both the events observed in the CoGeNT & CDMS direct detection experiments while evading constraints on annihilation rates from non-detection of gamma-rays by FGST is Asymmetric Dark Matter (ADM). In ADM, the contemporary dark matter consists of a particle, but not its anti-partner so it does not annihilate (the symmetric portion of the population annihilated in the early universe). Nevertheless, I will discuss how Asymmetric Dark Matter may leave its signature on stellar evolution giving a potential astrophysical signature of such a dark matter candidate. Time-permitting, I will also discuss self-interacting dark matter (SIDM), which is a dark matter particle with a large cross section (~1 barn) for scattering with itself. SIDM has been invoked as a possible means to alleviate some of the small-scale "challenges" to standard Cold Dark Matter (CDM) cosmology. I will discuss how SIDM is captured within the Sun and how neutrino telescopes can provide complementary constraints on some SIDM candidate models.

red galaxies

The Unbearable Lightness of Being: Direct detection of light dark matter

9/16/13
Felix Kahlhoefer
(U of Oxford, UK)

Motivated by the recent observation of a signal in the Si detectors of the CDMS-II experiment, I will review the difficulties of direct detection for light dark matter. While the observed events are consistent with being nuclear recoils due to scattering of Galactic dark matter particles, there is significant tension with the upper bounds from the XENON10 and XENON100 experiments. I will discuss the underlying assumptions for these results and point out under what conditions the tension between these experiments can be ameliorated or resolved. A particular focus will be on experimental uncertainties (for example concerning the ionisation yield Q_y) and uncertainties related to the dark matter velocity distribution. Finally, I will discuss various particle physics modifications of the interactions between DM and SM quarks which can bring XENON10/100 and CDMS-II into better agreement.

red galaxies

Radio frequency interferometry for measuring Antarctic albedo and detecting cosmic ray events

9/18/13
Jessica Stockham
(U of Kansas)

The ANtarctic Impulsive Transient Antenna (ANITA) experiment, a balloon-borne suite of horn antennas, is designed to detect radio frequency (RF) signals from the interaction of neutrinos with nucleons in the Antarctic ice sheet. Subsequent to the the ANITA II 2008-2009 flight, no neutrino events were discovered, but analysis did show the detection of cosmic ray air shower events. The majority of these events were detected as reflections from the ice surface. Reconstructing these reflected events requires analysis and modeling of the reflection properties of the air-ice interface. Using data obtained during the ANITA II 2008-2009 flight, the direct and reflected solar signals are employed to estimate the the power reflection coefficients as a function of incident elevation angle. The initial results of this analysis are discussed along with issues arising from the interferometric techniques. Current progress toward implementing a different interferometric technique, triple correlation, is presented as a method to potentially improve the analysis.

red galaxies

Revised predictions of ultra-high-energy neutrinos from gamma-ray bursts and the cosmic ray-neutrino connection

9/23/13
Mauricio Bustamante

The recent detection of ultra-high-energy (UHE) neutrinos by IceCube has marked the start of a new era: it is possible that the long-sought UHE neutrinos from cosmic accelerators are now starting to be seen. Among the accelerator candidates, gamma-ray bursts (GRBs) stand out as some of the most attractive: from their observed high luminosities (~10^52 erg/s) and inferred large magnetic fields (~10^5 G), they are likely sites where highly-accelerated protons (~10^21 GeV) could create neutrinos of similar energy through proton-photon interactions. The non-observation of neutrinos associated with GRBs has recently ruled out the simplest models of UHE neutrino emission from these sources. However, by taking greater care of the particle physics involved, the expected flux from a more sophisticated emission model lies still comfortably one order of magnitude below the current upper bounds, as shown by the recent ANTARES results. In this talk, I will briefly introduce NeuCosmA, our revised model of neutrino emission. Also, I will succinctly introduce a generalised model of cosmic ray (CR) emission from GRBs which allows for protons to "leak out" of the source, in spite of the magnetic confinement. Finally, I will touch upon the cosmic ray-neutrino connection, assuming a common origin for them in GRBs, and argue that the current UHECR observations and the bounds on the UHE neutrino flux might already be enough to put tension on several possibilities of CR and neutrino emission and propagation.

red galaxies

SNO+ and the search for the Majorana neutrino

9/24/13
Logan Sibley
(U Alberta)

One of the leading unanswered questions in the field of neutrino physics is whether the neutrino is equivalent to its anti-particle, a so-called Majorana fermion. The most promising experimental method to determine the nature of the neutrino is to search for the process of neutrinoless double beta decay, where two neutrons in an isotope decay to two protons via neutrino exchange, emitting just two electrons and violating lepton number conservation in the process. The field is currently rife with experiments exploiting this idea. To date, however, there has been only a single claim of observation from a subgroup of the Heidelberg-Moscow experiment investigating 76Ge, reporting a half-life of 2.23x10^25 years and effective Majorana neutrino mass of 320 meV. Recent results from the GERDA experiment, using refurbished Ge crystals from Heidelberg-Moscow, strongly disfavour this claim, leading to a combined Ge experiment half-life limit at 90% confidence of 3.0x10^25 years. Current experiments investigating 136Xe also disfavour this claim of observation. Joining the current generation of experiments with the aim of pushing down the effective Majorana mass limit, SNO+ is a kilotonne-scale liquid scintillator neutrino detector housed 2 km underground in Vale Canada Ltd.'s Creighton Mine near Sudbury, Ontario, Canada. Through re-purposing existing hardware in place for the now decommissioned Sudbury Neutrino Observatory (SNO), and employing a rigourous materials purification and selection program, SNO+ will investigate neutrinoless double beta decay of 130Te. Owing to its size, SNO+ expects a sensitivity to the effective Majorana neutrino mass below 100 meV with a 0.3% loading of natural Te after several years of data collection. Designed as a general purpose detector, SNO+ also has a robust physics program that includes investigations of solar and supernova neutrinos, and reactor and geo anti-neutrinos. Construction of the detector is nearly complete, with the first water-fill commissioning phase set to begin at the end of this year with the neutrinoless double beta decay phase following in late 2014. This talk will present a short overview of neutrinoless double beta decay and outline the current status and physics goals of the SNO+ experiment.

red galaxies

Revealing Core Collapse Supernova Progenitors Without Seeing Them

10/1/13
Iair Arcavi
(UC Santa Barbara)

Identifying the progenitors of the various types of core collapse supernovae (SNe) is an outstanding problem, hindering progress towards understanding the explosion mechanisms of these events. Direct progenitor detections are limited to few nearby cases, and this method has so far only robustly established the connection between red supergiants and Type IIP SNe. Statistical methods allow for some constraints to be put on progenitor scenarios of other SN types, with large samples illuminating certain aspects of the roles of binarity, mass and metallicity. In addition, new surveys such as iPTF are finding supernovae at very early times, a mere hours to days after the explosion. Observations on these timescales can probe the shock cooling emission, constraining the progenitor radius, the explosion physics and also Ni mixing. Together, these methods are teaching us about the progenitors of many SN types.

red galaxies

New Relics from Inflation

10/2/13
Liang Dai
(Johns Hopkins)

Cosmological observations strongly support the theory that an inflationary phase in the early Universe seeded the density inhomogeneities of the present Universe. However, the underlying physics that drove inflation remains poorly understood. A variety of motivations lead us to consider the possibility that inflation may have involved more than just one fundamental field. If so, then it is important to understand the possible imprints of these inflation relics on cosmic structures, as these may, if observed, help reveal the fundamental mechanism of inflation. I will present two examples of such imprints from inflation. One is a three-point correlation between some 'fossil' field and the density perturbation. Such a correlation can give rise to modulations over the sky of power in the cosmic microwave background anisotropies. The other example involves a correlation between the inflationary gravitational-wave background and primordial density perturbations. I will explain how gravitational waves generated by inflation can result in a physically-measurable quadrupolar anisotropy in the galaxy power spectrum.

red galaxies

Newborn Pulsars as sources of Ultrahigh Energy Cosmic Rays

10/4/13
Ke Fang
(Chicago)

The workings of the most energetic astrophysical accelerators in the Universe are encoded in the origin of ultrahigh energy cosmic rays (UHECRs). Current observations by the Auger Observatory, the largest UHECR observatory, show a spectrum that agrees with an extragalactic origin, as well as an interesting transition in chemical composition from light element to heavier element as energy increases. Candidate sources range from young neutron stars to gamma-ray bursts and events in active galaxies. In this talk, we will discuss newborn pulsars as the sources of ultrahigh energy cosmic rays. We will show that a newborn pulsar model naturally injects heavier elements and can fit the observed spectrum once propagation in the supernova remnant is taken into account. With the proper injection abundances, integrated cosmic rays from the extragalactic pulsar population can match observation in all aspects - energy spectrum, chemical composition, and anisotropy. We will also examine the fingerprints of their Galactic counterparts on cosmic ray spectrum . Lastly, we will discuss the multi-messenger smoking gun of this scenario - the detectability of high energy neutrinos from pulsars and magnetars.

red galaxies

Bright and dark: Satellite galaxies as a test of galaxy formation and the nature of dark matter.

10/4/13
Anna Nierenberg
(UC Santa Barbara)

I present our recent measurements of the spatial distribution and the cumulative luminosity function of satellites up to a thousand times fainter than their hosts, as a function of host stellar mass and morphology between redshifts 0.1 and 0.8, using imaging from the COSMOS fields and a rigorous statistical analysis. I will demonstrate how these measurements provide powerful new constraints for abundance matching and cosmological simulations in the context of both warm and cold dark matter, and how future measurements of faint satellite colors using CANDELS, will provide important distinguishing power between warm and cold dark matter models. In addition, I will present results from a complementary gravitational lens modeling project in which we use spatially resolved spectra obtained with OSIRIS at Keck to place new constraints on the subhalo mass function.

red galaxies

Distribution function approach to redshift-space distortions

10/15/13
Zvonimir Vlah
(ITP Zurich)

In galaxy clustering surveys redshift corresponds to the true distance according to the Hubble Law. In addition, peculiar velocities induced by the local gravitational potential are not associated with the Hubble flow and can cause distortions in redshift space. We study these distortions in phase space distribution function approach in order to model the power spectra of dark matter and halos. In this approach RSD of dark matter halos can be written as a sum over density weighted velocity moments correlators, with the lowest order being density, momentum density and stress energy density. Modelling of these contributing terms is done by combining perturbative methods and non-local biasing model to connect halos to the underlying dark matter distribution. In modelling the isotropic part of the RSD power spectrum we go beyond the Poissonian estimates of shot noise and allow for the scale dependence seen in the N-body simulation data. We present the results of RSD model for multipoles as well as dependence of the power spectrum on the amplitude and direction of the Fourier modes. Transforming these we also obtain the results in configuration space. In addition to the power spectra we also show the models for the velocity statistics in the resdhift space.

red galaxies

Exploring the Extreme Universe with Fermi

10/15/13
Julie McEnery
(University of Maryland)

Following its launch in June 2008, high-energy gamma-ray observations by the Fermi Gamma-ray Space Telescope have unveiled over 1000 new sources and opened an important and previously unexplored window on a wide variety of phenomena. These have included the discovery of an population of pulsars pulsing only in gamma rays; the detection of photons up to 10s of GeV from gamma-ray bursts, enhancing our understanding of the astrophysics of these powerful explosions; the detection of hundreds of active galaxies; a measurement of the high energy cosmic-ray electron spectrum which may imply the presence of nearby astrophysical particle accelerators; the determination of the diffuse gamma-ray emission with unprecedented accuracy and the constraints on phenomena such as supersymmetric dark-matter annihilations and exotic relics from the Big Bang. Continuous monitoring of the high-energy gamma-ray sky has uncovered numerous outbursts from active galaxies and the discovery of transient sources in our galaxy. In this talk I will describe the current status of the Fermi observatory, review the science highlights and discuss future opportunties with Fermi.

red galaxies

Imprint of unstable dark matter on large-scale structure and implications for subhalo properties

10/22/13
Mei-Yu Wang
(Indiana, Pittsburgh)

Although cold dark matter is known to describe large-scale observations well, its agreement with data on galactic scales is less clear. A possible solution to the galactic scales issues relies on altering the nature of dark matter, such as making it warm or self-interacting. To constrain these different dark matter models, it is important to look for complementary astrophysical constraints. I discuss a class of unstable dark matter models in which a dark matter particle decays into a slightly less massive stable dark matter particle and a comparably light particle, with lifetime the order of the age of the Universe. I will show that by combining SDSS Lyman-alpha forest measurements with WMAP data, we can place interesting and competitive limits on decaying dark matter (DDM) models. Because of its late-decay nature, this class of DDM models can have significant impact on galactic substructure while agreeing with observations of the high-redshift intergalactic medium (IGM) distribution. I will discuss the predictions of DDM models on the galactic scales and compare them with those from other DM models. I will also discuss possible improvement in model constraints using late-time phenomena with forthcoming weak lensing data and also the newly-released BOSS Lyman-alpha forest measurement.

red galaxies

Mapping the z~2 Cosmic Web with Lyman-alpha Forest Tomography

10/24/13
Khee-Gan Lee
(Max Planck Inst for Astronomy)

I will discuss the technique of Lyman-alpha forest tomography, in which the Lyman-alpha forest absorption from an extremely dense grid (>500 per sq deg) of background sources is used to make a full 3D 'tomographic' map of large-scale structure at z~2. Using empirical luminosity functions of QSOs and LBGs, I will show that at apparent depths of g~24, the background sources are separated by comoving transverse distances of ~3 h^-1 Mpc thus enabling mapping on that resolution. Using simulations, I will show that just S/N~4 per angstrom on g=24 background sources is sufficient to generate maps with ~3 h^-1 Mpc comoving. This requires just several hrs of integration on existing spectrographs on 8-10m telescopes, e.g. VLT-VIMOS and Keck-LRIS. I will introduce CLAPTRAP, a survey to map out 1 sq deg in the COSMOS field over a comoving volume of 10^6 h^-3 Mpc^3. The resulting maps can be used to study z~2 properties as a function of their large-scale environment, characterize the topology of large-scale structure, and find galaxy protoclusters.

red galaxies

Probing the initial conditions of the Universe using large scale structure

10/29/13
Nishant Agarwal
(Carnegie Mellon)

Primordial non-Gaussianity induces a scale-dependent bias in large scale structure (LSS) data. Recent work has shown that the exact form of this scale-dependence also helps distinguish between scenarios where a single field or multiple fields contribute to the curvature fluctuations, and encodes information about the initial state of inflationary perturbations. I will discuss work in which we use photometric data of luminous red galaxies and quasars in the Sloan Digital Sky Survey Data Release Eight (SDSS DR8) to constrain primordial non-Gaussianity and the scale-dependence of the bias, and its implications for different models of inflation and single field inflation with generalized initial conditions. For reliable cosmological parameter estimation from LSS, it is extremely crucial to account for various sources of contamination in the data --- I will also discuss a method to characterize unknown systematics which may persist in the data after correcting for known sources of contamination.

red galaxies

A Nearly Gaussian Hubble-patch in a non-Gaussian Universe

11/5/13
Marilena Loverde
(Chicago)

The statistics of density perturbations in our local patch of the universe may look radically different from those in the universe at large --- something called ``super cosmic variance." In particular, even a small level of non-Gaussianity can cause observations in our Hubble volume to be biased by mode coupling. The bias depends on the background value of the curvature potential -- something that is locally unobservable -- and can be large if the entire post inflationary patch is large compared with our Hubble volume. I present a few examples in which the statistics of density perturbations in our Hubble patch appear nearly Gaussian and consistent with observations, despite the fact that the statistics in the larger post-inflationary volume look very different. Finally, I'll show an explicit example, the curvaton scenario, where the mode-coupling bias can be understood simply.

red galaxies

A multi-messenger quest for the sources of the highest energy cosmic rays

11/8/13
Foteini Oikonomou
(University College London)

The origin of ultra high energy cosmic rays (UHECRs) remains unknown despite decades of experimental and theoretical research; their discovery will bring to light the nature of the Universe's most violent accelerators. In this talk I will discuss the observable signatures of UHECRs that can be used to constrain the nature and distribution of their yet unknown sources, focusing on the constraints imposed by the arrival directions of the highest energy cosmic rays detected at the Pierre Auger observatory in Argentina. Constraints on the sources of UHECRs may also come from the secondary particles (gamma-rays and neutrinos) that UHECRs produce during their propagation. I will present the results of a search for the signatures of UHECR acceleration in the gamma-ray spectra of blazars and discuss the implications for the detectability of such signatures with current and upcoming gamma-ray instruments.

red galaxies

Dissecting Galaxies With the Hubble Space Telescope

11/13/13
Julianne Dalcanton
(U of Washington)

7th Annual R. Jack and Forest Lynn Biard Cosmology and Astrophysics Lecture
Galaxies are complex systems of stars, gas, and dark matter. These three major components interact in many different ways, leading galaxies to have the structure and motions we see today. I will discuss the current paradigm for galaxy formation, and show how some of the most beautiful Hubble Space Telescope observations can be used to extract detailed histories of the nearest galaxies, providing some of the most rigorous constraints on the physics that controls galaxy formation.

red galaxies

Gas Retention and Accumulation in Dwarf Galaxies: Implications for Star Formation

11/19/13
Jill Naiman
(UC Santa Cruz)

The effective supply and retention of gas in shallow gravitational potentials is a problem with implications in a diverse set of astrophysical systems. In particular, the magnitude of gas flows into mature dwarf galaxies can have large impacts on the star formation histories in these systems. In this talk, computational techniques will be used to show how such such weakly bound gravitational structures might be able to accumulate gas effectively. The implications for star formation in dwarf galaxies after their incorporation into a larger host halo will be presented.

red galaxies

Cosmic Voids: Tracers of Large-Scale Structure

12/5/13
Nico Hamaus
(Paris Institute of Astrophysics)

Redshift surveys measure the location of millions of galaxies in the observable Universe, thereby constructing a three-dimensional map of its large-scale structure. This structure is characterized by dense clusters of galaxies, connected by filaments and sheets of lower number density. The remaining and dominant volume within this cosmic web is taken up by voids, vast regions of relatively empty space. While clusters, filaments and sheets have all entered different stages of non-linear evolution during cosmic history, voids represent structures that more closely related to the initial conditions of the Universe. I will discuss the prospects of considering cosmic voids as tracers of large-scale structure. While the clustering of voids alone yields a poor signal-to-noise ratio, when combined with the clustering statistics of galaxies, some interesting features emerge that may be useful for cosmological applications in the future. I will present some recent results obtained from numerical simulations and discuss their implications.

red galaxies

Real-space density profile reconstruction of stacked voids

12/6/13
Alice Pisani
(Paris Institute of Astrophysics)

In this talk I will briefly introduce the use of cosmic voids to constrain cosmology. I will then present a non-parametric, model-independent method to reconstruct the spherical density profiles of void stacks in real space, without redshift-space distortions. The method uses the expected spherical symmetry of stacked voids to build the shape of the spherical density profile of cosmic voids in real space without any assumption about the cosmological model. The reconstruction algorithm has been tested with both a toy model and a full dark matter simulation. I will present the result for the simulation: the reconstruction of the spherical density profile for a simulated stacked void in real space. I will also present a first application of the algorithm to reconstruct real cosmic void stacks density profiles in real space from the Sloan Digital Sky Survey (Sutter et al. 2012b) and discuss capabilities of the algorithm and possible future improvements. Reconstructed density profiles from real voids are the first step to study the spherically averaged dynamical structure of voids in real space. The reconstruction method does not make any cosmological assumption about the model, thus the density profile reconstruction of stacked voids in real space opens the way to better constrain the value of the Hubble constant and eventually cosmological models and new physics on current and future data sets.

red galaxies

Dwarf Galaxies are Trying to Kill Cold Dark Matter

12/9/13
James Bullock
(UC Irvine)

The cold dark matter (CDM) cosmological model has been very successful in explaining cosmic structure on large scales and over a vast span of cosmic time, but it has faced ongoing challenges from observations that probe the inner regions of dwarf galaxies in the local universe. Cosmological simulations that incorporate only gravity and collisionless CDM predict central densities that are too high to match constraints from galaxy dynamics. The solution could lie in baryonic physics: gravitational potential fluctuations associated with supernova feedback can lower central densities. However, it is not clear that this solution can work for the faintest galaxies, where basic energetic arguments suggest that feedback alone cannot solve the problem. Alternatively, the anomalous dark matter densities could be evidence of more complex physics in the dark sector itself. For example, elastic scattering from strong dark matter self-interactions can alter predicted halo mass profiles, leading to good agreement with observations across a wide range of galaxy mass. I will discuss ways forward for discriminating between these scenarios.

Indirect Detection of Dark Matter with Gamma Rays

12/10/13
Simona Murgia
(UC Irvine)

Evidence for dark matter is overwhelming. From experimental data we can infer that dark matter constitutes most of the matter in the Universe and that it interacts very weakly, and at least gravitationally, with ordinary matter. However we do not know what it is. Several theoretical models have been proposed that predict the existence of Weakly Interacting Massive Particles (WIMPs) that are excellent dark matter candidates. The existence of WIMPs can be tested indirectly, primarily through their annihilation or decay into photons. In this talk I'll present the latest results on these searches by Fermi LAT.

Neutrinos from GRBs, and the multi-messenger connection

1/21/14
Philipp Baerwald
(Penn State)

The detection of the first ultra-high energy neutrino events inside the IceCube telescope has finally opened neutrinos as a new "window" into the sky. With the neutrino as a new messenger, it is now possible to test astrophysical source models with several different types of messengers. However, to obtain meaningful results from the different messengers, detailed (particle physics) models of the sources are needed. At the example of GRBs, we will first discuss how the neutrino flux predictions are calculated based on gamma-ray observations and how they are used for current neutrino analyses. Then, we will use the particle physics involved to also obtain a prediction of the cosmic ray spectra self-consistently together with the neutrinos. Finally, we will discuss how the combination of neutrino, cosmic ray, and photon data can be used to derive strong constraints on the internal shock fireball model for GRBs and even rule out some of its forms.

The Fermi Bubbles: Possible Nearby Laboratory for AGN Jet Activity

1/24/14
Karen Hsiang-Yi Yang
(U. of Michigan)

One of the most important discoveries of the Fermi Gamma-ray Space Telescope is the detection of two giant bubbles extending 50 degrees above and below the Galactic center (GC). The symmetry about the GC of the Fermi bubbles suggests some episode of energy injection from the GC, possibly related to past jet activity of the central active galactic nuclei (AGN). Thanks to the proximity to the GC, the Fermi Bubbles are excellent laboratories for studying cosmic rays (CRs), Galactic magnetic field, and AGN feedback in general. Using three-dimensional magnetohydrodynamic simulations that include relevant CR physics, I will show how leptonic AGN jets can explain the key characteristics of the Fermi bubbles and the spatially correlated features observed in the X-ray, microwave, and radio wavelengths. I will also discuss how we use our simulations in combination with the multi-wavelength data to obtain constraints on the composition of the Fermi bubbles.

First measurement of pp neutrinos in real time in the Borexino detector

1/28/14
Pablo Mosteiro
(Princeton)

The Sun is fueled by a series of nuclear reactions that produce the energy that makes it shine. Neutrinos (ν) produced by these nuclear reactions exit the Sun and reach Earth within minutes, providing us with key information about what goes on at the core of our star. For decades since the first detection of solar neutrinos in the late 1960's, an apparent deficit in their detection rate was known as the Solar Neutrino Problem. Today, the Mikheyev-Smirnov-Wolfenstein (MSW) effect is the accepted mechanism by which neutrinos oscillate inside the Sun, arriving at Earth as a mixture of νe, νμ and ντ, the latter two of which were invisible to early detectors. Several experiments have now confirmed the observation of neutrino oscillations. These experiments, when their results are combined together, have demonstrated that neutrino oscillations are well described by the Large Mixing Angle (LMA) parameters of the MSW effect.
This talk presents progress towards the first measurement of pp neutrinos in the Borexino detector, which would be the first direct real-time measurement of pp neutrinos independent of other experiments. This would be, furthermore, another validation of the LMA-MSW model of neutrino oscillations. In addition, it would complete the spectroscopy of pp chain neutrinos in Borexino, thus validating the experiment itself and its previous results. We also report on a measurement of neutrons in a dedicated system within the Borexino detector, which resulted in an improved understanding of neutron rates in liquid scintillator detectors at Gran Sasso depths. This result is crucial to the development of novel direct dark matter detection experiments.

Seeing Gravitational Waves: Transients in the Local Universe

2/4/14
Mansi Kasliwal
(Observatories of the Carnegie Institution for Science)

The advent of wide-field synoptic imaging has re-invigorated the venerable field of time domain astronomy. Our framework of optical transients no longer has a wide six-magnitude luminosity "gap" between the brightest novae and faintest supernovae. Multiple new and distinct classes of very rare explosions have been uncovered just in the past few years. I review the surge of excitement (and debate) on the physics of these transients with unprecedented explosion signatures. "Gap transients" represent missing pieces in two fundamental pictures: the fate of massive stars and the evolution of compact binaries. Calcium-rich gap transients may even be the key to solving a long standing abundance problem in the intra-cluster medium. Two classes of gap transients are extremely red, hinting that the infrared dynamic sky is ripe for exploration. I conclude with the next frontier in gap transients --- discovering elusive binary neutron star mergers, a goal which may soon be within reach with coordination between the next generation of synoptic surveys and advanced gravitational wave interferometers. This search may literally be the 21st century gold rush!

Fast, Accurate Predictions of the Galaxy Power Spectrum

2/11/14
Juliana Kwan
(Argonna National Lab)

Two point galaxy clustering statistics are a key observable for large scale structure surveys. Unfortunately, they are very difficult to model accurately within the halo model and perturbation theory. In this talk, I will be presenting a new framework for calculating the galaxy power spectrum, called emulation, which can make predictions accurate to ~3%. Our technique uses a set of fully non-linear galaxy power spectra derived from applying the halo occupation model on a dark matter halo catalogue identified in a LCDM N-body simulation. A Gaussian process model then interpolates over the set of input power spectra. Unlike fitting functions, the cosmic emulation framework can be easily generalised to other problems and I will also describe a number of other projects currently in progress, such as emulating the redshift space power spectrum.

Discovery of Fermi Bubbles and Evidence for Past Activities in the Galactic Center

2/18/14
Meng Su
(KIASR (MIT), ITC (Harvard-Smithsonian Center for Astrophysics))

Analysis of data from the Fermi Gamma-ray Space Telescope revealed a pair of gigantic gamma-ray bubble structures, named the Fermi bubbles, each extending ~10 kpc above and below the Galactic center. I will present new results using five years Fermi-LAT data and multi-wavelength observations of the Fermi bubbles in X-ray, microwave, and radio, including updates from dedicated observations. New observations help us to distinguish hadronic from leptonic origin of the cosmic-ray electrons emitting gamma-ray/microwave emission, and constrain the magnetic field within the Fermi bubbles. I will also show our numerical simulations which demonstrate that the bubble structure could be evidence for past accretion events and outflow from the central supermassive black hole. Furthermore, we recently found evidence for large-scale collimated structure penetrating through the bubbles from the Galactic center from Fermi-LAT data. We have proposed to change the survey strategy of Fermi to increase the exposure at the inner Galaxy by more than a factor of 2. New survey strategy has been initiated since December 2013 and will last for at least one year. I will end up with a discussion of future gamma-ray space missions.

Beyond Dark Energy

2/19/14
Bhuvnesh Jain
(U. Penn)

The discovery that our universe is accelerating poses fascinating challenges for physics and astronomy. Vacuum energy, more generally called dark energy, is a possible explanation for the observed cosmic acceleration. Modifications to Einstein's general relativity are being explored as alternatives to dark energy. I will describe the theoretical motivations and experimental tests of gravity theories and other effects involving dark sector couplings. On large scales, they require a different take on cosmological observations such as gravitational lensing and large-scale structure in the universe. On much smaller scales the new tests of gravity use pulsating stars, rotating disk galaxies and other astronomical phenomena. I will describe how these diverse observations are being used to look "beyond dark energy".

Very High Energy Blazars: A Broadband Perspective

2/25/14
Amy Furniss
(UCSC)

Blazars, a type of active galaxy with a jet pointed toward the observer, are perplexing objects harboring relativistic particle populations with intrinsic characteristics which, despite more than 20 years of investigation, remain an enigma. These sources emit non-thermal radiation and display bright, variable emission at all energies. Blazars are the most commonly detected type of very high energy (VHE; E > 100 GeV) source and can be observed at these energies by imaging atmospheric Cherenkov telescopes such as VERITAS. A foundational understanding of the underlying acceleration mechanisms, particle environment, non-thermal emission and definitive extragalactic distance enable the use of these extraordinary objects to constrain the star formation history of the Universe through the indirect measurement of the extragalactic background light, the accumulated and reprocessed radiation of all starlight produced over the life of the Universe. I will summarize the results from a variety of innovative and complementary multiwavelength observations which can be used to address long-standing questions regarding the underlying acceleration mechanism, the emission environment and constituent particles within VHE blazar jets.

Constraints on the parameter space of axion dark matter

2/26/14
Kfir Blum
(Princeton / IAS)

I will discuss phenomenological constraints on the parameter space of axion dark matter. First, I will review how standard chiral perturbation theory relates the axion mass to the induced neutron electric dipole moment (nEDM). I will argue that this well known relation can only be avoided at the price of fine-tuning, and show that it has significant implications for proposed experimental searches for the oscillating nEDM induced by the background field of axion dark matter. I will then show that, if one is willing to accept this kind of fine-tuning, another constraint comes up by requiring that axion-driven operators in the chiral Lagrangian, that redshift up in the early Universe, do not ruin the success of Big-Bang Nucleosynthesis at z~10^10.

Order out of chaos:
Towards understanding galaxy formation in the cosmological context

3/4/14
Andrey Kravtsov
(Chicago)

Galaxy formation is a complex, hierarchical, highly non-linear process, which involves gravitational collapse of dark matter and baryons, supersonic, highly compressible and turbulent flows of gas, star formation, stellar feedback, as well as heating, cooling, and chemical processes that affect the gas and, indirectly, the stellar and dark matter distributions. Nevertheless, despite the apparent complexity of processes accompanying galaxy formation, galaxies exhibit a number of striking regularities, such as tight correlations between galaxy sizes, masses, luminosities, and internal velocities and surprisingly tight correlations between properties of stars and gas in galaxies and the mass and extent of their parent halos dominated by dark matter. Existence of such correlations indicates that powerful processes operate to bring order out of chaos. Understanding what these processes are and how they operate is not only fascinating scientifically, but is critical for interpreting the avalanche of current and future observations of galaxies across cosmic time. I will describe recent progress in our understanding of how such regularities can arise in a seemingly chaotic and nonlinear process of galaxy formation.

Elizabeth Fernandez

A Multiwavelength Understanding of the Epoch of Reionization

3/11/14
Elizabeth Fernandez
(Groningen)

Up until very recently, the Epoch of Reionization has been largely observationally unexplored . However, with advancements of modern telescopes, we are now able to observe this period of the Universe in multiple ways. While observations are still very challenging due to a host of foreground contaminants, combining observations at multiple wavelengths can lead to a greater understanding of the populations of stars and galaxies at these redshifts. I will describe two of these observables: the Cosmic Infrared Background, which is partially the integrated light from all stars and galaxies at high redshifts, and the 21cm Background, which results from emission from neutral gas. These observables, when paired with theory and simulations, can tell us about some of the first stars and galaxies that formed within our Universe.

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"Light WIMPs" in direct dark matter detection

3/18/14
Graciela Gelmini
(UCLA)

Four direct dark matter detection experiments, DAMA, CoGeNT, CRESST and CDMS-II-Si, find potential signals of "Light WIMPs" (Weakly Interacting Massive Particles with mass 10 GeV or lighter) while several other experiments, CDMS-II-Ge, CDMSlite, SuperCDMS, XEONON10, XENON100, LUX..., do not find any. Are all or some the positive and negative signals compatible with each other? I will review the experimental situation and compare the data for different particle candidates in a dark halo model dependent and in a dark halo model independent manner.

Using Millions of SDSS Halo Stars to Robustly Measure the Shape of the Milky Way's Dark Matter Halo

3/25/14
Sarah Loebman
(Michigan)

I will present detailed evidence from the Sloan Digital Sky Survey (SDSS) for the presence of a dark matter halo within Milky Way (MW). Using the number density distribution and kinematics of SDSS halo stars, my collaborators and I probe the dark matter distribution to heliocentric distances exceeding ~10 kpc and galactocentric distances exceeding ~20 kpc. Our analysis utilizes Jeans equations to generate two-dimensional acceleration maps throughout the volume; this approach is thoroughly tested on a cosmologically derived N-body+SPH simulation of a MW-like galaxy. We show that the known accelerations (gradients of the gravitational potential) can be successfully recovered in such a realistic system. The SDSS observations reveal that, in Newtonian framework, the implied gravitational potential cannot be explained by visible matter alone: the gravitational force experienced by stars at galactocentric distances of ~20 kpc is as much as three times stronger than what can be attributed to purely visible matter. Leveraging the baryonic gravitational potential derived by Bovy & Rix (2013), we show that the SDSS halo stars also provide a strong constraint on the shape of the dark matter halo potential. Within galactocentric distances of ~20 kpc, the dark matter halo potential is well described as an oblate halo with axis ratio q_DM=0.7+/-0.1. Thanks to precise two-dimensional measurements of acceleration for halo stars, we can reject MOND model as an explanation of the observed behavior, irrespective of the details in assumed in the interpolating function and the value of characteristic acceleration. In the era of Gaia and LSST, these techniques can be used to map the MW dark matter halo with a much better fidelity, and to a much larger galactocentric radius.

Review of the proton radius puzzle

3/27/14
Maxim Pospelov
(Victoria, Perimeter)

Recent measurements of the Lamb shift in the muonic hydrogen and deuterium revealed a puzzling discrepancy with similar measurements in e-p systems. This is often presented as a difference in the value for the proton charge radius. The origin of the discrepancy is not known, and in my talk I will cover possible scenarios for its resolution: an experimental error, "unusual" QCD effects, or new MeV-scale forces. For the latter, I describe a new idea for searches of MeV-scale force carriers using underground accelerators.

The Physics of Gas Sloshing in the Cores of Galaxy Clusters

4/1/14
John ZuHone
(NASA-Goddard)

Many X-ray observations of relaxed galaxy clusters reveal the presence of sharp, spiral-shaped discontinuities in the surface brightness of the X-ray emitting gas. Spectral analysis of these features shows that the colder gas is on the brighter side, hence they have been dubbed "cold fronts." These features arise naturally in simulations from the cool-core gas "sloshing" in the gravitational potential. Their sharpness and stability has important implications for the microphysics of the ICM. The sloshing motions may have other effects, such as contributing to the heating of the cluster core and the acceleration of relativistic particles. I will present simulations of gas sloshing in clusters, explain their formation and evolution, and discuss the implications for the physics of the ICM, including fresh results on heat conduction, viscosity, and radio mini-halos. I will also briefly discuss yt, an emerging software toolkit for analyzing astrophysical data from simulations and other datasets.

Statistically probing the merger history of the Milky Way

4/8/14
Facundo Gomez
(Michigan State)

Despite a wealth of observational information that is currently available, the details of the formation of our own Galaxy remain a puzzle. Thanks to the latest generation of stellar surveys it is now possible to study in detail how the Milky Way has evolved to become the galaxy we currently observe During the first part of this talk I will discuss how semi-analytic models of Galaxy formation, coupled to cosmological N-body simulations, could allow us to constrain the Milky Way merger history. Statistical model emulators are used to efficiently explore the multi-dimensional input parameter space of our model. We search for the sets of input parameters that can best reproduce the cumulative Luminosity Function (cLF) of satellite galaxies. Our results indicate that the determination of "best-fit" parameters is highly susceptible to the particular merger history of the Milky Way-like host. When comparing the resulting best-fitting models against independent sets of observational data, we find that only one of these models was able to simultaneously reproduce the stellar halo mass within 40 kpc of the Galactic center and the cLF. On the basis of this analysis it is possible to disregard certain models, and their corresponding merger histories, as good representations of the underlying merger history of the Milky Way. During the second part of this talk I will discuss about the perturbations that a minor merger event may induce in the phase-space distribution of Solar Neighborhood stars. In particular, I will show how the interaction between the Milky Way disc and the Sagittarius dwarf galaxy could qualitatively explain some of the radial and vertical perturbations identified in current observational data sets.

Cosmology with the Baryon Oscillation Spectroscopic Survey (BOSS)

4/15/14
Florian Beutler
(LBNL)

I will present the results of the BOSS-DR11 analysis which we published 4 months ago. I will also present measurements of the growth of structure through redshift-space distortions using the power spectrum multipoles. Such a measurement can be used to test General Relativity. Our measurements are in some tension with the expectation of LCDM and I will suggest ways in which this tension can be alleviated.

Constraints on Dark Matter from Merging Galaxy Clusters

4/22/14
Doug Clowe
(Ohio University)

Over the past decade, merging galaxy clusters have become one of the primary sources of data for constraining properties of dark matter particles as well as the force law of gravity on Mpc scales. Using the Bullet Cluster, I will demonstrate how merging clusters prove that dark matter makes up the majority of the mass of their systems independent of assumptions regarding the nature of the force law of gravity and place constraints on the self-interaction cross-section of dark matter. I will review the dozen merging clusters that have been studied since the Bullet Cluster, and discuss whether any of them show serious departures from a light-traces-mass paradigm that would cause significant problems for a LCDM universe.

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