CCAPP Seminars

# 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.

# 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.

# "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.

# Interpretation of standard problems associated with Milky Way dwarf spheroidals

4/29/14
Louis Strigari
(Indiana U.)

Improvements in theory and observations have put a new spin on the classical problems involving Milky Way dwarf spheroidals, and dwarf galaxies in general. In this talk, I will discuss what information can robustly be extracted from these observations, and how this information can be connected to the large scale cosmological model. I will close by discussing how this field will progress in the era of 30m class telescopes and with forthcoming galaxy surveys.

# High redshift starburst galaxies revealed by SPT, ALMA, and gravitational lensing

5/6/14
Joaquin Vieira
(Illinois, Urbana-Champaign)

The South Pole Telescope (SPT) has systematically identified a large number of high-redshift strongly gravitationally lensed starburst galaxies in a 2500 square degree cosmological survey of the millimeter (mm) sky. With ALMA, we have performed an unbiased spectroscopic redshift survey with these sources and determined that roughly 40% lie at z>4. Two sources are at z=5.7, placing them among the highest redshift starbursts known, and demonstrating that large reservoirs of molecular gas and dust can be present in massive galaxies near the end of the epoch of cosmic reionization. These sources were additionally targeted with high resolution imaging with ALMA, unambiguously demonstrating them to be strongly gravitationally lensed by foreground structure. We are undertaking a comprehensive and systematic followup campaign to use these cosmic magnifying glasses'' to study the infrared background in unprecedented detail, inform the condition of the interstellar medium in starburst galaxies at high redshift, and place limits on dark matter substructure. I will discuss the scientific context and potential for these strongly lensed starburst galaxies, give an overview of our team's extensive followup efforts, and describe our latest science results.

# Microlensing techniques: revealing the "black box"

5/27/14
Ana Mosquera

You know that microlensing techniques are powerful. You know that our group and collaborators have used them to set by the first time limits on quasar's X-ray emitting regions. And you know that currently you can only rely upon us to study the inner structure of AGNs. But, how does the microlesing machinery actually works? Under which assumptions do we fit and analyze the data? And why is our technique so robust? In my talk I'll answer to these questions following Mosquera et al. 2013.

# Magnetic Deflections of Ultra-High Energy Cosmic Rays

5/27/14
Michael Sutherland

The nature of cosmic rays are mysterious even more than a century after their discovery. At the highest energies ($E > 10^{18}$ eV), their composition and sources are unknown. Deflection in cosmic magnetic fields, even at these ultra-high energies, complicates source identification due to a direct dependence on the composition as well as uncertainties in the magnetic fields. For a nearby source, for example Centaurus A (Cen A), deflection from the extragalactic magnetic field is minimized. This allows for deflection studies of the Galactic magnetic field (GMF), which itself is capable of significantly altering UHECR trajectories. I will highlight a study of simulated UHECR trajectories from Cen A to Earth for a range of rigidities, allowing for primaries as heavy as Fe nuclei with energies exceeding 50 EeV. The Galactic magnetic field is modeled using the recent work of Jansson and Farrar which fitted its parameters from extragalactic Faraday rotation measures and WMAP7 synchrotron emission maps. This model also includes parameters for a detailed turbulent component. Aspects of the arrival direction distributions are examined for dependencies on rigidity and properties of turbulent field realizations.

# Galaxy intrinsic alignments: systematic nuisance or powerful probe?

6/3/14
Jonathan Blazek

The shapes and orientations of galaxies arise from complex processes on comparatively small scales. In the context of weak gravitational lensing measurements, large-scale correlations between these shapes, known as "intrinsic alignments" (IA), constitute the most significant astrophysical source of uncertainty and have the potential to degrade cosmological constraints. If sufficiently understood, however, IA can probe the physics of the formation and evolution of galaxies and their surrounding dark matter halos. IA may also provide a valuable tracer of large-scale structure. In this talk, I will outline why understanding IA is critical for current and future weak lensing surveys, including DES and LSST. I will describe recent and ongoing work in which we use both analytic modeling and observational data to make significant progress towards this goal.

# Quasars and their absorption lines: a legacy survey of the high redshift universe with X-shooter

6/3/14
Kelly Denney

Utilizing the X-shooter spectrograph on the VLT, we have obtained spectra of 100 z>3.5 QSOs with high S/N (95% of the reduced spectra have S/N>20 and ~50% have S/N>30). X-shooter is a unique, 3-arm echelle spectrograph that covers wavelengths from the UV cutoff ~3000A through K-band (2.48 microns) at R~6,000. This Large Programme represents the first major spectroscopic QSO survey in the rest-frame UV and optical at z>3.5. I will present our data and science goals, though given the time allotted, I will only be able to discuss in more detail some of our plans for this exquisite data set, which encompass (1) measurement of the matter power spectrum with the Ly-alpha forest at high redshift, including an independent measurement of cosmological parameters with a joint analysis of these and the Planck publicly released data; (2) determination of the incidence of MgII absorbers at z > 2.5 with unprecedented sensitivity to test predictions from the cosmic star formation rate; (3) investigation of the physical environments of the quasars, including, e.g., accurate measurements of black-hole masses, luminosities and metal abundances in a homogeneous sample; and (4) measurement of the universe's opacity at the Lyman limit and constraint of the UV background via the proximity effect.

# AGN-STORM - Space Telescope and Optical Reverberation Mapping of NGC 5548

6/10/14
Gisela DeRosa

Active Galactic Nuclei are the spectacular manifestation of accreting black holes and can tell us many things about their central powering engines. Reverberation mapping is a powerful technique to study the region near the supermassive black holes, allowing a full geometric and kinematic modeling of the broad line region gas through the study of variations of the emission line profiles. After a brief review of reverberation mapping methods, I will focus on AGN-STORM, a program centered on 180 daily HST observations designed to study in unprecedented details the broad line region in one AGN: NGC 5548. I will describe the observing strategy, the challenges and the aims of this ambitious project and present preliminary results.

# Detecting absorption signatures of warm / hot gas circum-galactic gas in COS archival data

6/10/14
Stephan Frank

A large fraction of the baryons at the low redshift universe (z=1, and below) has thus far escaped our heroic detection efforts. Simulations predict that part of these "missing" baryons may be located in areas of the temperature-density parameter space that would produce weak UV absorption features when seen against bright background sources like QSOs. Here, I am going to report on our ongoing project to detect such a weak signature of this gas, focusing on a specific transition (NeVIII). Instead of presenting polished results, however, I will focus on the method itself we have specifically developed for this prupose ('agnostic stacking'), but also highlighting its broader applicability for similar searches.

# Model Independent Measurements of Angular Power Spectra

6/17/14
Sheldon Campbell

Spatial fluctuations of astrophysical signals are a powerful probe of source distributions, radiation production mechanisms, and propagation effects. The precision of measuring angular power spectra is currently estimated as a combination of shot noise, instrument systematics, and cosmic variance. We show that an important contribution, dependent on the finite statistics of the experiment, has been neglected. These new results allow for improved estimates of sensitivities to angular power by statistics-limited observations, such as for high-energy gamma rays.

# First exoplanet similar to Uranus

6/17/14

We know exoplanets similar to both inner rocky planets of Solar System as well as Jupiter and Saturn. However, the long orbital periods of Uranus and Neptune make their analogs inaccessible to methods that depend on periodic phenomenon i.e. radial velocities and transits. Also direct imaging is not sensitive enough. I present the first discovery of extrasolar planet that has orbit and mass similar to Uranus using gravitational microlensing method. Moreover, the host star has a relatively nearby stellar or brown dwarf companion. All the basic properties of the lens triple system can be understood without detail modeling.

# Dynamical Modeling of the Broad Line Region in AGNs with Reverberation Mapping Data

6/24/14
Kate Grier

Both theoretical and observational evidence suggests that galaxies and their central supermassive black holes are connected. In order to understand these connections, we must have accurate measurements of supermassive black hole masses in objects across the observable universe. All black hole mass measurements in distant galaxies are made using emission lines in active galactic nuclei (AGN) -- however, the unknown conditions within the broad line-emitting region could be a source of serious systematic errors in black hole mass measurements in these objects. Reverberation mapping methods have the capability of both yielding black hole mass easurements as well as information about the broad line region itself. I will discuss the use of dynamical modeling techniques with reverberation mapping data to probe the geometry and kinematics of the broad line region in active galactic nuclei to help better constrain black hole mass estimates in these galaxies and understand the physics of the BLR, highlighting preliminary results using data from a 2010 reverberation campaign carried out here at OSU.

# Understanding the Detector Background for Astrophysical MeV Neutrino Detection

6/24/14
Shirley Li

Background rejections are crucial for MeV neutrino detection. When muons travel through matter, their energy losses lead to nuclear breakup (“spallation”) processes. Subsequent beta decays can lead to detector backgrounds that mimic neutrino signals, and isotopes with long lifetimes are especially difficult to cut. In a recent paper from Super-Kamiokande collaboration, a correlation between the spallation event position and a peak in the prior muon Cherenkov light profile was found. We calculate the rates of isotopes produced by muons and their secondaries in Super-Kamiokande and study the properties of electromagnetic showers induced by muons. A better theoretical understanding of these processes will help in developing new techniques to reduce detector backgrounds.

7/1/14
Paul Sutter

Voids are the large, underdense regions in the cosmic web, and they are potentially powerful cosmological probes due to their intimate connection to the growth of structure, their domination by dark energy, and their relative lack of systematics. I will present our latest work to identify voids in galaxy redshift surveys, our efforts to understand their fundamental nature and their connection to dark matter underdensities, and an overview of many diverse cosmological applications, including gravitational lensing, the ISW effect, and the Alcock-Paczynski effect.

# Clustering, Proximity, and Balrog

7/1/14
Eric Suchyta

I will present work in progress about what happens to galaxy clustering when the influence of proximity effects in the data are included. I will touch on a new software package we have developed which is directly related to problem at hand. I will demonstrate in simple terms what is difficult about the problem and what the answer must look like.

# Fishing for the FIR Line Deficit in the Local Swimming Hole: Heating and Cooling in the ISM

7/8/14
Kevin Croxall

The physical state of interstellar gas and dust is dependent on the processes which heat and cool this medium. The principal mechanisms responsible for the heating and cooling of this gas are thought to be the injection of photoelectrons from dust and far-infrared line emission, respectively. In standard practice, we express the efficiency of the photoelectric effect as the ratio of the strong [CII] cooling line emission to thermal dust emission, [CII]/TIR. As the average temperature of dust grains increases a deficit appears in the ratio of [CII]/TIR, according to studies of the global properties of galaxies. While several solutions to this occurrence have been suggested, its cause has not been clear. However, galaxies host a complex ISM, that is most certainly inhomogeneous. Deeper understanding of this deficit requires observations with better spatial resolution to disentangle environments with different radiation fields. Using data from the Herschel space observat ory we investigate the [CII] deficit in nearby galaxies.

# Testing the wedge effect on future 21cm BAO surveys

7/8/14
Hee-Jong Seo

Baryon acoustic oscillations (BAO) provide a robust standard ruler with which to measure the acceleration of the Universe. The BAO feature has so far been detected in optical galaxy/qso surveys. Intensity mapping of neutral hydrogen emission with a ground-based radio telescope provides another promising window for measuring BAO at redshifts of order unity for relatively low cost. Although very promising in terms of performance per cost, the major challenge for this method is the severe foreground contamination. I will discuss the effect of the foregrounds on 21cm surveys when they are not removed properly.

# Unorthodox weak-lensing applications in DES

7/15/14
Peter Melchior

The Dark Energy Survey (DES) will soon start the second season of observations. I'll review the current state of the survey and summarize the efforts to control and improve the quality of observations and data processing. I will then discuss ideas how to exploit the existing data for weak-lensing purposes in several ways other than cosmic shear.

# An Ultra-high Energy Neutrino Search with the ARA Testbed

7/22/14
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 GZK effect. The detection of these UHE cosmic neutrinos will add to the understanding of the sources and physics of UHE cosmic rays. ARA uses the radio Cherenkov technique to search for UHE neutrinos by deploying radio frequency (RF) antennas at 200m depth in the Antarctic ice and searching for impulsive RF signals. A prototype ARA Testbed station was deployed in the 2010-2011 season and the first design-level ARA stations were deployed in the 2011-2012 and 2012-2013 seasons. I will present the results of one of the first neutrino searches with 2011-2012 ARA Testbed data.

# Hot galactic winds constrained by the X-ray luminosities of galaxies and ram pressure acceleration of cold clouds

7/22/14
Dong Zhang

Galactic superwinds may be driven by very hot outflows generated by overlapping supernovae within the host galaxy. We use the Chevalier & Clegg (CC85) wind model and the observed correlation between X-ray luminosities of galaxies and their SFRs to constrain the mass loss rates across a wide range of star formation rates (SFRs), from dwarf starbursts to ultra-luminous infrared galaxies. We show that for fixed thermalization efficiency and mass loading rate, the X-ray luminosity of the hot wind scales as Lx ~ SFR2, significantly steeper than is observed for star-forming galaxies: Lx ~ SFR. Using this difference we constrain the mass-loading and thermalization efficiency of hot galactic winds. For reasonable values of the thermalization efficiency (<~ 1) and for SFR >~ 10 M_sun/yr we find that \dot{M}hot/SFR <~ 1, significantly lower than required by integrated constraints on the efficiency of stellar feedback in galaxies, and potentially too low to explain observations of winds from rapidly star-forming galaxies. Moreover, we highlight that the CC85-like hot wind is unlikely the mechanism in accelerating neutral cold outflows in most starbursts observed by Na D absorption surveys, expect for some local dwarf starbursts.

# Recent progress on Magnification in the Dark Energy Survey

7/31/14
Eric Huff

Magnification is shear's neglected cousin, and by ignoring this lensing measurements ignore half of their potential signal. There are good reasons for this, but recent progress on magnification with Dark Energy Survey data holds out the prospect of magnification's achieving parity with shear. In this talk, I will describe the hybrid image simulations that make this feasible, and show preliminary magnification results using DES data.

# Gyrochronology in the Kepler Era: What Can Stellar Rotation Do for You?

7/29/14

Cool, single main sequence stars have rotation periods that increase as they age. The technique of gyrochronology uses the observed relationship between rotation period, stellar color, and age to date old field stars based on two key assumptions: 1) that all targets can be treated as single main sequence stars that spin down as a function of time, and 2) that the relations can be calibrated on systems of solar age and younger and extrapolated to old stars, where data has traditionally been sparse. With the recent availability of space-based photometry that provides both rotation periods (from stellar spot modulation) and independent ages (from asteroseismology), we are in a unique position to test and better calibrate rotation as a tool. I focus, in particular, on how an understanding of observational selection effects and behavior of rotation across all stellar types is critical for the calibration and interpretation of gyrochronological ages.

# Cross-correlating Planck, SPT, DES, Fermi and low-redshift galaxy surveys

7/31/14
Aurelien Benoit-Levy

By deflecting the trajectories of the CMB photon from the last scattering surface, gravitational lensing imprints statistical signatures of the matter distribution in the observed temperature and polarization anisotropies of the CMB. Extracting this signature permits the reconstruction of the lensing potential, a powerful probe of the matter distribution. Matter distribution can also be probed by galaxy surveys thus providing additional information that can be correlated with the CMB lensing potential. In this talk I will present some aspects of these cross-correlations focusing on the complementary of DES and Planck/SPT. I will also present some recent work that focuses on the correlation of the gamma ray sky observed by the Fermi satellite and catalogues of nearby galaxies.

# Understanding the Magnetic Variability of M and L dwarfs

8/5/14
Sarah Schmidt

M and early-L dwarfs are often active, revealing the presence of magnetic fields through both quasi-static emission from their chromospheres and coronae in addition to dramatic flares. Even the quasi-static emission exhibited by these low mass stars is intrinsically variable on timescales ranging from minutes to possibly even decades. I will briefly discuss current and future work to understand the magnetic variability of M and L dwarfs through photometric surveys for flares and spectroscopic monitoring for variations in the Halpha emission lines.

# Improved limits on sterile neutrino dark matter by Fermi-GBM

8/5/14
Kenny Ng

Sterile neutrinos with mass in the keV range are a well motivated dark matter candidate. Interestingly, these cannot be completely stable, though the lifetimes are very long. The decays produce an X-ray line that provides a distinctive signature. Stringent limits were set using Chandra, XMM-Newton, and INTEGRAL. However, there is a gap in sensitivity for the mass range 20 to 40 keV (with line energy 10 to 20 keV), because this is outside the sensitivity range of the fore-mentioned missions. For the first time, we show that it is possible to use Fermi Gamma-ray Burst Monitor (GBM) data to search for such lines in this gap. Our preliminary result show that we can improve the limit on sterile neutrino decay rate by about an order of magnitude.

# Cosmic Rays and Neutrinos as Complementary Probes of Ultra-High Energy Astrophysics

8/12/14
Nathan Griffith

Ultra-high energy cosmic ray and neutrino spectra provide us with a complementary set of information that can be used to uncover a variety of information about ultra-high energy phenomena. This work uses fits to the Pierre Auger Observatory's 2013 data to generate neutrino spectra. Then, looking through the lens of next generation neutrino detectors (EVA, ARA), the ultra-high energy parameters of source distribution and source spectrum are inspected.

# An All-Sky, Multi-wavelength Astronomy Computational Engine

8/12/14
Demitri Muna

Astronomy produces extremely large data sets from ground-based telescopes, space missions, and simulation. The problem is that no one institution can host all of this data, let alone have the resources to properly manage it. The result is that applying analyses against full data sets across the wide range of wavelengths available is either beyond the resources of most astronomers or currently impossible. Simply having an extremely large volume of data available in one place is not sufficient; one must be able to make valid, rigorous, scientific comparisons across very different data sets from very different instrumentation. This talk will describe a framework of distributed data and distributed computation for astronomers.

# From Nexus to Hopf: on the structure and dynamics of the Cosmic Web

8/19/14
Rien van de Weijgaert
(Kapteyn Institute, University of Groningen)

The Cosmic Web is the fundamental spatial organization of matter on scales of a few up to a hundred Megaparsec, scales at which the Universe still resides in a state of moderate dynamical evolution. galaxies, intergalactic gas and dark matter exist in a wispy weblike spatial arrangement consisting of dense compact clusters, elongated filaments, and sheetlike walls, amidst large near-empty void regions. This seminar will describe recent work on the structure and dynamics of the Cosmic Web. For the analysis of its complex and multiscale structural pattern, we invoke concepts from computational topology and computational geometry. We apply the explicit multi-scale -- parameter-free and scale-free -- Nexus/MMF Multiscale Morphology formalism to dissect the cosmic mass distribution into clusters, filaments, walls and voids. This results in a systematic study of the evolving size and volume distribution of these structural components. Subsequently, we assess the mass and halo distribution in the filaments and walls, and follow their evolution. To study the dynamical evolution of the cosmic web, we have developed an updated adhesion model of cosmic structure formation based on Voronoi and Delaunay tessellations. With this we can systematically follow the outline of the emerging cosmic web and its morphological components. This provides a systematic assessment of the sensitivity of the cosmic web to different cosmologies and/or as a function of power spectrum. We conclude with a short discussion of the detection of galaxy spin alignments with the filaments in which galaxies are embedded, the most direct manifestation of the influence of filaments on the properties of galaxies.

# Cosmic Ray Populations in Three Starbursting Galaxies

8/26/14
Tova Yoast-Hull
(Wisconsin)

M82, NGC 253, and Arp 220 are often associated with each other due to similarities in the intense starburst environments contained within each galaxy. Dense concentrations of young massive stars, strong magnetic fields, and high radiation fields characterize their starburst nuclei. Additionally, both M82 and NGC 253 have been detected in gamma-rays with Fermi. Despite their similarities, the interstellar medium and effects of galactic winds differ in these galaxies. However, these distinctions are vital to understanding the role of cosmic ray interactions and the observed radio and gamma-ray spectra from each galaxy. I will discuss results of my single-zone models of the cosmic ray populationsof the starburst nuclei and their implications for future gamma-ray and neutrino observations.

# Photometric quasars and primordial non-Gaussianity

8/26/14
Boris Leistedt
(UCL)

Quasars are highly biased tracers of the large-scale structure and therefore powerful probes of the initial conditions and the evolution of the universe. However, current spectroscopic catalogues are relatively small for studying the clustering of quasars on large-scales and over extended redshift ranges. Hence one must resort to photometric catalogues, which include large numbers of quasars identified using imaging data but suffer from significant stellar contamination and systematic uncertainties. I will present a detailed analysis of the photometric quasars from the Sloan Digital Sky Survey, and the resulting constraints on the quasar bias and primordial non-Gaussianity. The constraints on $f_{\rm NL}$, its spectral index, and $g_{\rm NL}$, are the tightest ever obtained from a single population of quasars or galaxies, and are competitive with the results obtained with WMAP, demonstrating the potential of quasars to complement CMB experiments. These results take advantage of a novel technique, 'extended mode projection', to mitigate the complex spatially-varying systematics present in the survey in a blind and robust fashion. This work is a new step towards the exploitation of data from the Dark Energy Survey, Euclid and LSST, which will require a careful mitigation of systematics in order to robustly constrain new physics.

# Lessons in Near-Field Cosmology from Simulating the Local Group

9/9/14
Shea Garrison-Kimmel

Studies of the Milky Way (MW) and Andromeda (M31) galaxies, along with their associated satellites and nearby dwarf galaxies, have proven immensely useful for constraining the cosmology of the Universe, particularly on small scales. I will present a number of simulations, many of which are a part of the ELVIS Suite, cosmological zoom-in simulations of Local Group-like volumes of MW/M31 pairs. Using these, and other simulations, I will highlight existing tensions within the LCDM paradigm, as well as illustrate how simulations can provide links between near-field and deep-field observations.

# The evolution of early-type galaxies: a strong lensing perspective

9/16/14
Alessandro Sonnenfeld
(UCSB)

Early-type galaxies are believed to grow as a result of mergers, but the details of this process are still largely unknown. Do the mergers involve galaxies of comparable mass (major) or are they dominated by small systems (minor)? Is there dissipation (wet) or not (dry)? Different processes leave different signatures on the mass structure of early-type galaxies. Gravitational lensing provides a unique way to detect these signatures. The SL2S project measured the evolution of the mass profile of massive early-type galaxies during the last 7 billion years, including constraints on the mean density slope, dark matter fraction, inner dark matter slope and stellar IMF. Based on collected data, we find that theoretical models for the evolution of early-type galaxies through dry mergers alone are unable to reproduce the observed trends. Additional physical processes, likely related to baryonic physics, are necessary to match the entire set of observables.

# The DECam Legacy Survey & Image reduction using the Tractor

9/23/14
Dustin Lang
(CMU)

I will introduce the DECam Legacy Survey, a large public imaging program that will observe over 6,000 square degrees in grz, to ~2 mags deeper than SDSS. The survey will be critical for DESI (the Dark Energy Spectroscopic Instrument) and should provide good legacy value to the community. I will show some preliminary data reductions using "the Tractor", a code for generative modeling of multi-band, multi-epoch image collections.

# Satellite quenching and the life cycle of dwarf galaxies.

9/30/14
Colin Slater
(Michigan)

In the past ten years the known population of Local Group dwarf galaxies has expanded substantially, both to greater distances from the Milky Way and to lower dwarf masses. This growing sample allows us to study the dwarf system as a population, and ask if we can see in aggregate the signs of processes that would otherwise be difficult to trace in dwarfs individually. Following this strategy I will discuss how the quenching of dwarf galaxies can be modeled and understood at the population-level, and how we use that to constrain how possible quenching mechanisms must work if they are to reproduce the Local Group system that we see. I will also discuss work done with Pan-STARRS to study the role of infalling satellites in disrupting the outer disk of the Milky Way and creating the so-called "Monoceros Ring".

# Eavesdropping on the Dark Sound of the Universe

10/7/14
Francis-Yan Cyr-Racine
(JPL)

Self-interacting dark matter (DM) has been put forward as a way to address potential problems with the Cold DM paradigm on sub-galactic scales. For a broad class of models the interactions between DM particles are mediated by a light force carrier. At temperatures above its mass, the force carrier effectively behaves as a dark radiation (DR) component that tightly couples to the DM, forming an almost perfect fluid. We expect this combined DM-DR system to give rise to sound waves propagating throughout the cosmos until DM kinematically decouples from the DR. Much like the standard baryon acoustic oscillations, these dark acoustic oscillations (DAO) imprint two characteristic scales, the sound horizon of dark matter and its Silk damping scale, in the matter density field. We find that linear cosmological data and CMB lensing put strong constraints on existence of DAO features in the CMB and the large-scale structure of the Universe. We also study, for the first time, the nonlinear evolution of cosmological structures in this type of theories by performing N-body simulations including both the modified matter power spectrum and the DM self-interactions. We find the resulting phenomenology to be far richer then in the cold or warm DM case. We conclude by discussing how quasar strong gravitational lenses could be used to probe this class of dark matter models.

# The Sad Story of the Cosmic EUV Background

10/14/14
Matthew McQuinn
(Washington)

After reionization, a largely uniform ~1 Rydberg background pervaded the Universe, keeping the intergalactic hydrogen extremely ionized. The characteristics of this background depend on the properties of the sources (quasars and galaxies) and the absorbers (Lyman-limit systems). Modeling the sources is difficult, but I will argue that the absorbers seem to be captured in cosmological simulations, at least at high redshifts. Quick evolution (on a time < 0.1 H(z)^-1) in the ionizing background is observed at z=6, which has (controversially) been interpreted as indicating the end of reionization. I will explain why this evolution must owe to the absorbers and discuss how such quick evolution could arise. We can directly measure the ratio of the 1Ry to 4Ry ionizing background by comparing the hydrogen Lyman-alpha forest to the HeII Lyman-alpha forest in the same sightline. Previous attempts to measure this ratio found order-of-magnitude fluctuations on 1-10 Mpc scales, in conflict with theoretical expectations. I will show that these previous analyses were flawed, and that the data is in fact consistent with the expectation of an almost uniform 1 and 4 Rydberg background at z~2.5. Finally, I will discuss whether the EUV background affects galaxy formation, as has been speculated. Unfortunately, all does not end well for the cosmic EUV.

# Multi-wavelength analysis of supernova remnant MSH11-61A

10/17/14
Katie Auchettl
(CfA Harvard)

Due to its centrally bright X-ray morphology and limb brightened radio profile, Galactic supernova remnant MSH 11-61A (G290.1-0.8) is classified as mixed morphology. HI and CO observations have determined that the SNR is interacting with a molecular cloud found towards the north and southwest regions of the remnant. As observations of thermal and non-thermal emission of SNRs have provided increasing support in favour of cosmic rays being accelerated at its shock front, SNRs known to be interacting with molecular clouds provide an effective target for detecting and studying the production of gamma-rays from the decay of a neutral pion into two gamma-ray photons. I report on the detection of gamma-ray emission coincident with MSH 11-61A using 70 months of data from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. To investigate the origin of this emission, we perform broadband modelling of its non-thermal emission considering both leptonic and hadronic cases and concluding that the gamma-ray emission is most likely hadronic in nature. Additionally we also present our analysis of an archival Suzaku observation of this remnant. Our investigation shows that the X-ray emission of MSH 11-61A arises from a two temperature component plasma consisting of a hot, ejecta-rich plasma that is still ionising and a cool, recombining ISM component.

# The Extragalactic Gamma-ray Background AND Searching for Satellite Galaxies of the Milky Way in the Dark Energy Survey

10/21/14
Keith Bechtol
(Chicago)

Part 1: The extragalactic gamma-ray background (EGB) is generated by the superposition of all extragalactic gamma-ray emissions and thus provides a window on both the demographics and evolution of non-thermal phenomena across cosmic time. A significant fraction of the total EGB intensity has now been resolved into individual sources using the Fermi LAT, and there is an emerging understanding of how fainter members of the established extragalactic gamma-ray source classes can account for the residual approximately isotropic component of the gamma-ray sky, called the isotropic gamma-ray background (IGRB). The latest measurement of the IGRB spectrum with the Fermi LAT from 100 MeV to 820 GeV exhibits a high-energy cutoff feature consistent with the attenuation of high-energy gamma rays by pair-production on the IR/optical/UV extragalactic background light. High-energy cosmic neutrinos will be essential to see beyond this gamma-ray horizon to greater distances and higher energies.

Part 2: Searches for indirect dark matter signals in the direction of Milky Way satellite galaxies provide some of the strongest constraints on the annihilation cross section of dark matter derived from gamma-ray observations. Milky Way satellite galaxies have the advantages of low astrophysical backgrounds, the ability to constrain the dark matter abundance and distribution from the kinematics of member stars, and the opportunity to combine observations of multiple satellites in a joint-likelihood framework to increase sensitivity. The discovery of additional Milky Way satellites in wide-field optical imaging surveys may provide substantial advances for indirect dark matter searches. I will discuss a matched-filter maximum-likelihood algorithm to search for and characterize ultra-faint galaxies in the ongoing Dark Energy Survey, which will cover 5000 square degrees in the relatively less explored south Galactic cap.

# Studying the Expansion of the Universe with BOSS quasars

10/23/14
Andreu Font-Ribera
(Lawrence Berkeley National Lab)

After six years of observations, the Baryon Oscillation Spectroscopic Survey (BOSS) ended last summer, and will soon make its data public (SDSS Data Release 12). During these years, it has used the SDSS telescope to obtain spectra of 1.5 million galaxies to get very accurate measurements of the Baryon Acoustic Oscillations (BAO) scale at redshift z ~0.5. At the same time, BOSS observed over 184 000 high redshift quasars (z>2.15) with the goal of detecting the BAO feature in the clustering of the intergalactic medium, using a technique known as the Lyman alpha forest (LyaF). In this talk I will overview several results from the LyaF working group in BOSS, including the measurement of BAO at z=2.4 both from the auto-correlation of the LyaF (Delubac et al. 2014), and from its cross-correlation with quasars (Font-Ribera et al. 2014). From the combination of these studies we are able to measure the expansion rate of the Universe 11 billion years ago with a 2% uncertainty.

# Relation Between Galaxy Cluster Optical Richness and SZ Effect

10/28/14
Neelima Sehgal
(Stonybrook)

Accurate galaxy cluster masses are important for their use as precision cosmological probes. Measuring the SZ effect and optical richness of clusters are two methods used to estimate cluster masses, and thus it is natural to ask whether these methods yield consistent results. Using data from the Atacama Cosmology Telescope (ACT) to measure the SZ effect, we test the consistency of the two methods. We find that the SZ flux from the Max-BCG optically-selected cluster sample is both lower than expected from the richness-mass relation, and lower than measured by the Planck satellite. Possible implications of these results will be discussed.

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