CCAPP Seminars

# The Characterization of the Gamma-Ray Signal from the Central Milky Way: A Compelling Case for Annihilating Dark Matter

1/20/15
Tim Linden
(Chicago)

In scenarios where dark matter particles can annihilate to produce standard model particles, the galactic center of the Milky Way is expected to provide the highest flux from dark matter in the sky. This has allowed galactic center observations to set extremely stringent limits on the parameters of the dark matter particle. Recently, we have worked on gamma-ray observations from the Fermi-LAT telescope, and have detected a significant extended excess, which is spherically symmetric around the position of the galactic center, and does not trace any known astrophysical emission profile. In this talk, I will summarize the current status of these observations and discuss dark matter and astrophysical interpretations of the data. I will show forthcoming results which strongly constrain the properties and the possible interpretations of the observed excess. Finally, I will posit upcoming tests which will strongly suggest, or rule out, a dark matter interpretation.

# Voids and Scaling in the Halo Model

1/27/15
Jim Fry
(Florida)

The popular halo model has implications that go beyond its usual applications to the galaxy autocorrelation function or power spectrum. I will examine how the model holds up in its predictions for higher order statistics of both mass and galaxy number, and I will revisit the hierarchical scaling behavior of void probabilities.

# The Fermi Bubbles and Future Gamma-ray Telescopes

2/3/15
Meng Su
(MIT)

The Fermi Bubbles are a pair of giant lobes at the heart of the Milky Way, extending roughly 50 degrees north and south of the Galactic Center, and emitting photons with energies up to 100 GeV. This previously unknown structure could be evidence for past activity of the central supermassive black hole. I will outline the current state of the multiwavelength observations of this structure, and discuss theoretical proposals and numerical simulations for their nature and origin. The Fermi Bubbles was discovered using data from the successful Fermi Gamma-ray Space Telescope, which has proved the great potential of studying astrophysics, cosmology, and fundamental physics in high energy gamma rays. I will talk about three future gamma-ray missions: DAMPE, HERD, and PANGU, and comment on what science could be learned from these future missions.

# Scrutinizing the Relationship Between Galaxies and Supermassive Black Holes

2/10/15
Jillian Bellovary
(Vanderbilt)

Supermassive black holes (SMBHs) have a ubiquitous presence in massive galaxies, but their formation and evolutionary history remain mysteries. One of the strongest observed trends between SMBHs and their host galaxies is the tight relation between black hole mass and the velocity dispersion of the stellar spheroid (aka the M-Sigma relation). While this relation hints at a fundamental link between galaxy and SMBH growth, there are also some challenges regarding scatter and outliers. I will present evidence that the M-Sigma relation is not the clear-cut trend it seems to be; for example, the orientation of galaxies on the sky affects the value of velocity dispersion by up to 30%. Additionally, the existence of SMBHs in dwarf galaxies and galaxies without spheroids challenges the standard paradigm of SMBH-galaxy coevolution. I will offer some alternative methods of forming and growing SMBHs which can provide explanations for these puzzling outliers.

# Radio and X-ray Studies of Type II-P Supernovae: What They Reveal About the Parents

2/17/15
Alak Ray
(Tata Institute)

I will describe our ongoing work on studying X-ray and radio emission from a class of supernovae that forms almost half of all core collapse supernovae, namely type II Plateau SNe. We have carried out these with Chandra, EVLA and GMRT telescopes. Because these bands probe the interaction of the SN with the medium it exploded in, they provide valuable information about the star that exploded and the nature of the medium. Our Chandra observations of SN 2004dj for the first time measured the separate contributions of thermal emission from the SN shocks and the power-law nonthermal part arising out of accelerated particles. For this and a few other SNe the combination of radio and X-ray measurements indicate the extent of equipartition between magnetic fields amplified by the shock and the relativistic particles accelerated by it.

# Chasing our Cosmic Dawn: Opening the 21cm cosmological window on the universe

2/24/15
Danny Jacobs
(Arizona State)

The Epoch of Reionization (EoR) marks when the first stars ionized the primordial hydrogen half a billion years after the big bang. Direct observation of cosmological hydrogen is possible via the 21cm line and is now being hotly pursued as a new cosmological probe. Danny Jacobs is helping to lead observations with both the Precision Array for Probing the Epoch of Reionization (PAPER) and the Murchison Widefield Array (MWA). PAPER currently holds the deepest limits on the epoch of reionization power spectrum, while the MWA is leading the charge towards understanding foregrounds at a level necessary for imaging large scale structure. The two intertwined themes in these new instruments are the degree to which experimentation is an essential component of the science process and the ascendance of the software pipeline. Experiments currently under-way to refine array sensitivity include high-bandwidth forward-modeling of instrumental response, developing high level heuristics for data flagging, accelerating imaging pipelines, pushing more analysis steps into real-time systems, and in-situ calibration with external drone-mounted transmitters. Lessons learned and systems developed for PAPER and the MWA are being incorporated into the next generation Hydrogen Epoch of Reionization Array (HERA) that will yield 20 times the sensitivity of first generation arrays and also into the upcoming Square Kilometer Array.

# Shedding Light on Distant Galaxies with ~400,000 SDSS Quasars

3/3/15
Britt Lundgren

Distant quasars backlight the Universe over most of cosmic time, revealing the evolving gas distribution of the cosmic web. Intervening metal absorption lines in quasar spectra can provide sensitive tracers of the gaseous processes regulating star formation in foreground galaxies to high redshift, but observational difficulties have traditionally limited comparisons to the stellar properties of the absorbing galaxies. The extraction and statistical analysis of absorption line systems from 377,809 unique quasar spectra in the Sloan Digital Sky Survey (SDSS I-III) has recently catalyzed our understanding of the physical environments of the most prolific metal absorption species (e.g., Mg II, C IV) observed in optical quasar spectra. I will present recent stacking and clustering measurements made possible by the vast quasar absorption line samples from the SDSS, and present new, direct observations of Mg II absorber host galaxies at high redshift using the Hubble Space Telescope. Together these studies reveal compelling links between strong Mg II absorbers and large-scale star formation-driven outflows, providing insights into the role of feedback in the evolution of galaxies from z~2.

# The Role of Dwarf-Dwarf Interactions in the Evolution of Low Mass Galaxies

3/10/15
Sabrina Stierwalt
(Virginia)

I will present the initial results from TiNy Titans, the first systematic study a sample of interacting dwarf galaxies and the mechanisms governing their star formation. Mergers of massive galaxies provide a significant mode of galaxy evolution and are observed to inspire intense starbursts and significant rearranging of the galaxies' gas and dust. However, despite the fact that mergers among low mass galaxies outnumber those between massive ones, whether these effects occur in the shallower gravitational potential wells of dwarf galaxies remains completely unconstrained. A few intriguing examples of dwarf-dwarf interactions exist in the literature, but the efficiency of gas removal and the enhancement of star formation in dwarfs via pre-processing (i.e. dwarf-dwarf interactions occurring before the accretion by a massive host) has never been studied for a uniformly selected sample of dwarfs. Our multiwavelength approach gathers high resolution optical, UV, and radio imaging to probe the effects of interactions on the star formation and ISM in a complete sample of dwarf pairs selected from the Sloan Digital Sky Survey. We find star formation is enhanced in paired dwarfs over isolated dwarfs to an even greater extent than is observed in massive galaxies, but the dwarfs involved in interactions still have large gas reservoirs (and thus capacity for future star formation). Our interacting dwarfs tend to be low metallicity and thus offer a unique window into modes of star formation that were important at earlier epochs.

# It's Always Darkest Before the Cosmic Dawn

3/17/15
Josh Dillon
(MIT)

Realizing the promise of 21 cm cosmology to provide an exquisite probe of astrophysics and cosmology during the cosmic dark ages and the epoch of reionization has proven extremely challenging. We're looking for a small signal buried under foregrounds orders of magnitude stronger. We know that we're going to need very sensitive, and thus very large, low frequency interferometers, which present their own set of difficulties. And, as I will explain, we're going to need a rigorous statistical analysis of the maps we make to extract interesting cosmological information. I will discuss the steps we've taken to overcome these obstacles with early data from the Murchison Widefield Array by isolating foregrounds to a region of Fourier space outside a clean "epoch of reionization window." Additionally, I will present some of most recent and exciting predictions for what 21 cm cosmology can tell us as we move to larger telescopes like the Hydrogen Epoch of Reionization Array and higher redshifts.

# On Neutrino Decay and Other Non-Unitary Effects on Neutrino Propagation

3/24/15
Andre de Gouvea
(Northwestern U)

After providing a brief overview of the neutrino physics landscape - what we know and what we know we don't know - I discuss in some detail the possibility that neutrino propagation is not unitary, e.g., the neutrinos could, generically, decay, and review what is currently known about the lifetime of the different neutrino mass-eigenstates.

# Primordial non-Gaussianity in the CMB and Large-Scale Structure

3/31/15
Kendrick Smith
(Perimeter Inst)

I'll give a pedagogical review of inflation and explain how its physics can be constrained by searching for "primordial non-Gaussianity", i.e. differences between the statistics of the initial curvature field in our universe and the statistics of an ideal Gaussian field. Then I'll talk about observational CMB constraints, including some new results from Planck. Finally I'll discuss future prospects for improving Planck constraints with large-scale surveys such as Euclid and LSST.

# The Zen of Core Collapse: How to See A Supernova That Doesn't Happen

4/7/15
Elizabeth Lovegrove
(UCSC)

It now seems likely that stars over 8 solar masses, rather than all exploding as some form of core-collapse supernova, have a range of explosion probabilities that depend on mass. Different masses of progenitor may explode with regular CCSNe energies, explode with much lower energies, or fail to explode entirely. Narrowing down these possible outcomes and associating them with stellar masses is important to galactic evolution models and a key step in achieving accurate end-to-end core-collapse simulations. But making progress on this question requires a large sample of observed supernova progenitors, and these are hard to come by. True observational limits, too, require being able to see not only supernovae that happen but also supernovae that don't. In this talk I will present and discuss results from the CASTRO simulation code on both transients from completely-failed supernovae as well as shock breakouts from faint supernovae, a promising channel for retrieving progenitor information.

# Exploring the Third Dimension: Spectroscopic Needs for Imaging Dark Energy Experiments?

4/14/15
Jefferey Newman
(Pittsburgh)

This talk will explore a number of applications of wide-area spectroscopic surveys, such as those which the Dark Energy Spectroscopic Instrument (DESI) will enable, to solving key problems for imaging dark energy experiments. First, I will discuss the problem of photometric redshifts (a.k.a. photo-z's): i.e., estimates of the redshifts of objects based only on flux information obtained through broad filters. Higher-quality, lower-scatter photo-z's will result in smaller random errors on cosmological parameters; while systematic errors in photometric redshift estimates, if not constrained, may dominate all other uncertainties from these experiments. In this talk, I will describe the key challenges for training and calibrating photometric redshift algorithms in the next two decades, and describe how DESI can help us address these challenges. Second, I will discuss the contributions the DESI instrument can make to LSST supernova studies by measuring spectroscopic redshifts for large samples of supernova hosts, which would require comparatively modest time allocations. Finally, I will describe the LSST Dark Energy Science Collaboration, highlighting how all of us can get involved now in preparing for this extraordinarily rich imaging dataset.

# The Cosmic Laboratory: Probing Fundamental Physics with Large-Scale Structure and the CMB

4/21/15
Roland de Putter
(JPL)

In the current era of precision cosmology, the Universe on large scales has become a unique probe of many fundamental physics questions that are hard or even impossible to address with conventional terrestrial experiments. In this seminar, I will discuss examples of what this "Cosmic Laboratory" teaches us about neutrino physics, inflation, dark matter and dark energy. I will discuss the following two topics in particular detail. First, I will discuss how currently, and for the foreseeable future, cosmology places the tightest bounds on the absolute mass scale of neutrinos. I will pay specific attention to the robustness of these bounds with respect to assumptions about the primordial power spectrum and thus inflation. Secondly, I will explain what it would take for a galaxy survey to use primordial non-Gaussianity to distinguish between single-field and multi-field inflation and I will introduce a specific proposal for such a survey, called SPHEREx.

# Observational Tests of Cosmic-ray Diffusion in the Magellanic Clouds

4/24/15
Laura Lopez
(OSU Astronomy)

Cosmic rays (CRs) play an important role in the interstellar medium: they ionize dense molecular gas, they are responsible for the light elements in the periodic table, and they account for 20% of the ISM energy budget. However, the means by which CRs are first accelerated and then transported through external galaxies are not well understood. I will present results from a recent study of the Magellanic Clouds to constrain CR transport using Fermi gamma-ray observations. I will show how we have characterized the spatial distribution of gamma rays in the LMC and SMC and used the findings, in conjunction with available multiwavelength data, to constrain CR transport based on how the emission depends on physical parameters, such as gas density, massive star formation, magnetic field structure, and turbulence properties.

# Searching for Dark Matter with Gamma Rays

4/28/15
Andrea Albert
(SLAC)

There is overwhelming evidence that non-baryonic dark matter constitutes ~27% of the energy density of the Universe. Weakly Interacting Massive Particles (WIMPs) are promising dark matter candidates that may produce gamma rays via annihilation or decay in the Universe. A detection of gamma rays from WIMPs would not only confirm the existence of dark matter through a non-gravitational force, but also indicate the existence of physics beyond the Standard Model. I will present recent Fermi-LAT Collaboration results from WIMP searches including looking for gamma-ray spectral lines and gamma-ray excesses in areas of large dark matter concentration like the Galactic center and dwarf spheroidal galaxies.

# Interpretation of IceCube results in the multi-messenger context

5/1/15
Walter Winter
(DESY Zeuthen, Germany)

The discovery of high-energetic cosmic neutrinos is one of the recent major breakthroughs in science. We discuss the concept of the neutrino production, and interpret recent results taking into account the information from other messengers (gamma-rays, cosmic rays). For example, one question is if these neutrinos come from the most powerful accelerators in the universe, i.e., the ones which can accelerate cosmic rays to the highest observed energies. We also discuss future perspectives for neutrino astronomy.

# The PAU Survey at the William Herschel Telescope

5/4/15
Ignacio Sevilla
(Illinois)

We present PAUCam: a multi-narrow band camera designed to conduct a photometric survey from the 4m William Herschel Telescope, starting this year. The scientific goals (which include intrinsic galaxy alignments, magnification and redshift space distortions), camera design and current status will be described.

# The future of weak gravitational lensing in cosmology

5/5/15
Ludo van Waerbeke
(UBC)

Gravitational lensing by large scale structures is poised to play a central role in the future of precision cosmology, to help constraining modified theories of gravity, the neutrino mass, quantifying the dark energy equation of state and a lot more. It is quite possible however that gravitational lensing will first shed light on some of the complex astrophysical processes taking place in galaxy and galaxy cluster formation, before it can reach the high precision needed for dark energy and modified gravity tests. After a short introduction of the basic concepts and ideas, I will discuss some of the recent and most promising developments and what challenges lie ahead for future surveys such as LSST, Euclid or WFIRST.

# New Physics at IceCube

5/7/15
Bhupal Dev
(U. of Manchester)

The recent observation of ultra-high energy neutrino events at IceCube has spurred a lot of interest in the scientific community. From a particle physics viewpoint, several exotic phenomena have been proposed to explain the data. For a reliable interpretation, it is however important to first scrutinize the Standard Model (SM) expectations carefully, including all known theoretical and experimental uncertainties. In this talk, we discuss the compatibility of the 3-year IceCube dataset with some well-motivated flavor and spectral compositions of the astrophysical flux within the SM framework, and show that the SM interactions are sufficient to explain the current data within the known uncertainties. Using this result, we can derive constraints on some New Physics scenarios, which are otherwise difficult to probe at the LHC or other existing low-energy experiments.

# Cosmological Constraints on Newton's Gravitational Constant for Matter and Dark Matter

5/12/15

In this talk I will present a study using cosmological data of the gravitational interaction in ordinary and dark matter sectors. In the first part I will present a new constraint of Newton's gravitational constant by making use of the latest CMB data from the Planck experiment and independent constraints coming from Big Bang Nucleosynthesis and low redshift experiments. In the second part of the talk I will focus on the dark matter sector, giving a constraint to the dark matter equivalence principle and long-range fifth forces.

# The Fermi Galactic Center excess

5/15/15
Ilias Cholis
(Fermilab)

The possible gamma-ray excess in the inner Galaxy and the Galactic center suggested by Fermi-LAT observations has triggered great interest in the astro-particle physics community. Among its various interpretations have been WIMP dark matter annihilations, gamma-ray emission from a population of millisecond pulsars, or emission from cosmic rays injected in a sequence of burst-like events or continuously at the GC. Given that the galactic diffuse emission is the dominant (by an order of magnitude or more) at any direction greater than 2 degrees from the GC understanding the background systematics has been a vital missing piece in the discussion. I will present the first comprehensive study of model systematics coming from the Galactic diffuse emission in the inner part of our Galaxy and their impact on the inferred properties of the excess emission at Galactic latitudes between 2 and 20 degrees and energies 300 MeV to 500 GeV. I will show both theoretical and empirical model systematics, which are deduced from a large range of Galactic diffuse emission models and a principal component analysis of residuals in numerous test regions along the Galactic plane. The hypothesis of an extended spherical excess emission with a uniform energy spectrum is compatible with the Fermi-LAT data in the region of interest at 95% CL. Assuming that this excess is the extended counterpart of the one seen in the inner few degrees of the Galaxy, a lower limit of 10 degrees (95% CL) can be derived on its extension away from the GC. In light of the large correlated uncertainties that affect the subtraction of the Galactic diffuse emission in the relevant regions, the energy spectrum of the excess is equally compatible with both a simple broken power-law of break energy 2.1 $\pm$ 0.2 and with spectra predicted by the self-annihilation of dark matter, implying in the case of $\bar{b}b$ final states a dark matter mass of 49$^{+6.4}_{-5.4}$ GeV. I will also briefly discuss interpretations of this excess, based on annihilating DM, leptonic CR outburst and a population of millisecond pulsars.

# Simulating Massive Neutrinos

5/19/15
Simeon Bird
(Carnegie)

Massive neutrinos make up a fraction of the dark matter, but due to their large thermal velocities, cluster significantly less than cold dark matter (CDM) on small scales. An accurate theoretical modelling of their effect on structure formation is required to fully exploit large-scale structure data. I will discuss different methods to add neutrinos to cosmological simulations, finishing with one which is accurate for current cosmological mass bounds and requires minimal extra computational cost. I will then talk about the impact of neutrino masses on cluster counts and perhaps the Lyman-alpha forest.

# Gravitational Signals from Noise in the Hubble Diagram

5/21/15
Edward Macaulay
(Univ of Queensland)

Understanding the nature of the dark universe requires precise measurements of the background expansion history, and also the growth rate of density fluctuations. In this talk, I'll consider both regimes with supernova lensing for the OzDES spectroscopic survey - which is measuring the redshifts of hundreds of supernova and thousands of galaxies identified by the Dark Energy Survey. I'll start by reviewing the more established method of growth rate measurements with Redshift Space Distortions, and discuss possible tension between RSDs and expectations from Planck CMB measurements. I'll then consider how OzDES can place novel constraints on the growth rate and amplitude of density fluctuations by correlating noise in the supernova Hubble diagram with the gravitational effects of lensing and peculiar velocities expected from the observed density field.

# Not with a Bang, but a Whimper: Evidence for Low-energy Supernovae

5/22/15
(OSU/CCAPP)

I will present new HST and Spitzer late-time imaging of SN 2008S and NGC 300-OT, the prototypes of a class of stellar transients whose true nature is debated. Both objects have faded below the luminosity of their progenitors and are now undetected in both the near and mid-IR, providing strong evidence that these events were terminal. This, combined with the mass constraints on the progenitors, indicates that this class of transients likely arise from electron-capture supernovae.

# Indirect Detection of Dark Matter Using MeV-Range Gamma-Ray Telescopes

5/22/15
Kimberly Boddy
(Hawaii)

The astrophysics community is considering plans for a variety of gamma-ray telescopes in the energy range 1--100 MeV, which can fill in the so-called "MeV gap" in current sensitivity. We investigate the utility of such detectors for the study of low-mass dark matter annihilation or decay. For annihilating (decaying) dark matter with a mass below about 140 MeV (280 MeV) and couplings to first generation quarks, the final states will be dominated by photons or neutral pions, producing striking signals in gamma-ray telescopes. We determine the sensitivity of future detectors to the kinematically allowed final states. In particular, we find that planned detectors can improve on current sensitivity to this class of models by up to a few orders of magnitude.

# Weighing the Giants: Anchoring Galaxy Cluster Cosmology

5/26/15
(KICP Chicago)

The gas mass fractions and the distribution in mass and redshift of the galaxy cluster population provide powerful probes of cosmology, constraining the cosmic matter density, the amplitude of the matter power spectrum, properties of dark energy, and the mass of neutrinos, among other parameters. Historically, these tests have been limited by the absolute accuracy of cluster mass determinations. Here, mass measurements from weak lensing have an advantage over estimates based on observations of the intracluster medium (ICM), because the former are nearly unbiased and can be straightforwardly tested against simulations. I will describe recent cosmological constraints obtained from an analysis of X-ray selected cluster samples, incorporating extensive gravitational lensing data from the Weighing the Giants project -- the first cluster cosmology study to consistently integrate a lensing mass calibration, including a rigorous quantification of all systematic uncertainties. The results highlight the power and potential of galaxy clusters, which constrain both the expansion of the Universe and the growth of cosmic structure, and their complementarity with other probes such as type Ia supernovae, large-scale galaxy surveys, and the cosmic microwave background.

# Probing the nature of AGN coronae through future X-ray and sub-mm observations

5/29/15
Yoshiyuki Inoue
(ISAS / JAXA)

While the cosmic X-ray background is likely to originate from individual AGNs, the origin of the cosmic MeV gamma-ray background is not fully understood. We proposed that AGNs having non-thermal electrons in coronae may explain the MeV background. Such non-thermal electrons are expected to exist if a corona is heated by magnetic reconnections. However, the sensitivity of current MeV gamma-ray instrument is not sufficiently good to detect the expected power-law tail in the MeV band from individual AGNs. Furthermore, the heating mechanism of coronae in AGNs is still unknown, although magnetic reconnection heating is one possibility. In this talk, I would like to introduce how we can probe the origin of the MeV background and the nature of AGN coronae such as magnetic field and non-thermal content through future observations by ASTRO-H and ALMA.

# High energy neutrinos from extra-galactic astrophysical sources

5/29/15
Irene Tamborra
(Amsterdam)

The IceCube neutrino telescope recently discovered a flux of astrophysical neutrinos with energies up to few PeV. In light of the new born high-energy neutrino astronomy era, I will discuss the expected high-energy neutrino emission from extra-galactic astrophysical sources as well as our chances to unveil the physics of the cosmic accelerators by employing neutrinos and their photon counterparts.

# Neutron Astronomy with IceTop

6/2/15
Michael Sutherland (OSU Physics)

IceTop can detect an astrophysical flux of neutrons from Galactic sources as an excess of cosmic ray air showers arriving from the source direction. Neutrons are undeflected by the Galactic magnetic field and can typically travel 10 ($E$ / PeV) pc before decay. Two searches through the IceTop dataset are performed to look for a statistically significant excess of events with energies above 10 PeV ($10^{16}$ eV) arriving within a small solid angle. The blind search method covers from -90$^{\circ}$ to approximately -50$^{\circ}$ in declination. A targeted search is also performed, looking for significant correlation with candidate sources in different target sets.

# Honing in on the flavor composition of high-energy astrophysical neutrinos: the view from theory

6/2/15
Mauricio Bustamante (OSU Physics)

After years of searching, IceCube has recently detected the first high-energy astrophysical neutrinos, in the form of a diffuse flux in the range between 100 TeV and 2 PeV. While still in its infancy, neutrino astronomy opens an exciting new window to the Universe. One of the issues that IceCube has recently started to look into is the flavor composition of the flux: what is the proportion of electron-, muon-, and tau-flavor in the signal. This will reveal information about the physical conditions at the cosmological neutrino sources. In this talk I will present some broad considerations, coming from simple theoretical arguments, that show that the number of possible flavor compositions of the incoming flux is surprisingly small. This is true even in the presence of many types of potential new physics effects in the neutrino sector. These arguments provide theoretical guidance that can be used to constrain the experimental flavor searches.

# The Era of Accurate Cosmology?

6/9/15
Jonathan Blazek (OSU Physics)

Several great successes of the past decade have placed us firmly in the era of precision cosmology. An upcoming generation of cosmological surveys - including LSST, DESI, Euclid, and WFIRST - promise tremendous statistical power. But will we be able to harness this power? Without significant progress on several astrophysical and observational issues, we may find ourselves with extremely precise (and expensive) measurements that are systematically biased. In this talk, I will briefly discuss a few of the primary goals of these upcoming surveys along with the some of the questions we must understand to achieve these goals. In particular, I will focus on correlations between intrinsic galaxy shapes, which must be included when interpreting weak lensing measurements. I will describe recent work in modeling these correlations and discuss future steps.

# Preliminary Results on the Ages of Ultracool Dwarfs from SDSS

6/9/15
Sarah Schmidt (OSU Astronomy)

The ages of ultracool dwarfs (the smallest stars and the warmest brown dwarfs) are particularly interesting due to the degeneracy in mass, age, and luminosity at spectral types M7-L3. We examine the ages of these low mass from the BOSS Ultracool Dwarf sample of 13000 late-M and early-L dwarfs using a combination of colors, kinematics, and spectral features. I will discuss some preliminary results from the BUD sample, including an examination of kinematic differences between late-M and early-L dwarfs and a spectroscopic search for young, low gravity objects and low-metallicity subdwarfs.

# From data to theory at the cosmic dawn

6/16/15
Paul Sutter (OSU Physics)

Understanding the epoch of reionization is extremely difficult due to significant observational challenges and only a vague theoretical picture of the underlying physical processes. Fortunately, in the past year there have been many developments that address these difficulties. As examples I will discuss HERA, a proposed radio interferometer designed specifically to observe this epoch, and a new semi-blind Bayesian method for foreground removal and signal recovery. Finally, I will present some ideas for extracting physically meaningful quantities from the upcoming measurements.

# Crowdfunding Physics with Fiat Physica

6/24/15
Mark Jackson (Fiat Physica)

Theoretical physics suffered budget cuts of nearly 25% in 2014. Researchers report spending as much as 75% of their time writing grant proposals. Labs want to hire new talent but don't have the funds. With steep declines in funding, physics and its many derivative sciences are unable to rely on the support of grants alone. Yet a vast community of science enthusiasts exists who want to get involved at the ground floor of discovery.
In this talk I will be introducing Fiat Physica, the new crowdfunding platform connecting scientists, educators, and communicators with these avid science enthusiasts. Fiat Physica provides the unique opportunity to build a supportive, engaged community who cares about your research, invention, or other scientific endeavor. The success and adoption of new findings, technologies, and initiatives often lie in the non-financial support they receive. Crowdfunding allows you to raises funds, support and awareness in one combined effort. Unlike generic crowdfunding sites, Fiat Physica drives targeted traffic directly to your campaign to amplify your campaign's reach. Our niche blog and social media channels attract visitors to your campaign who are already interested in what you have to offer.

# The ExaVolt Antenna: Concept and Development

6/30/15
Carl Pfendner (OSU Physics)

In the past decade, searches for the cosmogenic neutrino flux produced by the interactions of ultra-high energy cosmic rays with the cosmic microwave background have not yet resulted in detection. Radio detection of ultra-high energy neutrinos provides a cost-effective means of probing a large effective volume. The Antarctic Impulsive Transient Antenna (ANITA) balloon-borne experiment, with sensitivity to neutrinos with energies >1019 eV, has provided some of the most stringent limits on cosmogenic neutrino production models by searching for coherent radio Cherenkov signals produced by the Askaryan effect in Antarctic ice. The ExaVolt Antenna (EVA) is a mission concept to extend the sensitivity of balloon-borne radio neutrino detection to energies 1017 eV. EVA uses a novel antenna design that exploits the surface area of the balloon itself to provide a reflector antenna with 30 dBi gain (compared to 10 dBi on ANITA). I will present recent developments in this detector concept including results of a scale model hang test.

# The luminosity function of satellite galaxies to z = 1.5

6/30/15
Anna Nierenberg (OSU Physics)

The standard cold dark matter model predicts that halos should contain large numbers of subhalos, characterized by a steep mass function. In contrast, the visible satellites of the Milky Way have a much flatter mass function. The solution to this so-called "missing satellite" problem is most likely tied to the fact that galaxy formation becomes more inefficient in low mass halos, due to a complex combination of cooling, star formation, and feedback processes. It may also involve a modification to the standard CDM model. Distinguishing between these alternatives, and even quantifying the nature of the problem, has been hampered by the fact that the lowest mass satellites are only well measured in our own Galaxy and at low redshift. I discuss my current work to use the near-IR HST CANDELS survey in order to study the properties of luminous satellites down to unprecedented depths and look-back times. I will be presenting some *all new* very preliminary measurements of the luminosity function of faint (sub SMC luminosity) satellite galaxies to redshift 1.5, and comparing with theoretical predictions from Millennium and a warm dark matter simulation.

# Is the Galactic Bulge Devoid of Planets?

7/7/15
Matthew Penny (OSU Astronomy)

Gravitational microlensing surveys have comparable sensitivity to planets orbiting stars in both the Galactic bulge and disk. I will show that the distribution of measured and inferred distance estimates to microlensing planet hosts differs substantially from what one would naively expect. I will outline a number of possible solutions to this puzzle, including that planet abundance may depend on a star's birth environment or perhaps more simply that the distance estimates may be unreliable. I will end by discussing how upcoming microlensing campaigns by Spitzer and K2 will help to resolve this issue.

# Zel'dovich decomposition: Probabilistic segmentation of the cosmic web into clusters, filaments, walls, and voids

7/7/15
Peter Melchior (OSU Physics)

I will present a novel method to analyze the cosmic web, based on the well-known Gaussian Mixture Model (GMM). By distinguishing GMM components with oblate, prolate or spherical shape, I can assign probabilities for any test sample to reside in walls, filaments, or clusters. I will demonstrate the method by decomposing the entire BOSS survey and discuss the potential of the method for photometric surveys, in particular DES. I will also give an outlook to a number of cosmological and astrophysical studies that are enabled with such a decomposition.

# Cosmology with Baryon Acoustic Oscillation Scale Measurements: Current Status and Future Prospects

7/14/15
Ashely Ross (OSU Physics)

I will describe how measurements of the baryon acoustic oscillation (BAO) scale embedded in the distribution of galaxies can be used to constrain cosmological parameters, especially the nature of dark energy. I will then describe the current state-of-the BAO measurements, which have been made using data from the Sloan Digital Sky Survey (SDSS) I-III. I will conclude by describing results to look forward to in the future, including those using the completed data set of the SDSS-III baryon oscillation spectroscopic survey (BOSS), data from the SDSS-IV extended BOSS, and data from the Dark Energy Survey.

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

7/14/15
Nathan Griffith (OSU Astronomy)

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 astrophysics. Via a model that employs probability tables calculated by CRPropa, this work uses fits to the Pierre Auger Observatory's 2013 data to generate neutrino spectra. Then, looking through the lens of current and next generation neutrino detectors (ANITA, ARA EVA), the parameters of source evolution and source spectrum cutoff at ultra-high energies are inspected.

# The Sensitivity of Astrophysical Anisotropy Signals to Spectral Lines

7/21/15
Sheldon Campbell (OSU Physics)

There has recently been new progress in the theoretical understanding of the statistical uncertainty for measurements of the angular power spectra of sources in high energy astrophysics experiments. The implications of these results for anisotropy experiments are explored; in particular, we'll discuss using the detected radiation's angular distribution to detect a weak spectral line in a diffuse background. Applied specifically to the problem of observation of a line from annihilating dark matter in the diffuse gamma-ray background, anisotropy analyses will be shown to be important for unravelling dark matter information from their annihilation signatures.

# The AGN Space Telescope and Optical Reverberation Mapping Project

7/28/15
Kelly Denney (OSU Astronomy)

Several members of the department are involved in a monumental reverberation mapping project (PI - B.M. Peterson) that consisted of ~170 HST/COS orbits and >1000 supporting SWIFT and ground-based observations across the UV/optical wavelength range. This project represents the most detailed (in terms of combined wavelength and temporal coverage) study of reverberation mapping of a single target, namely, NGC 5548, a nearby Seyfert 1 galaxy. While I am not the primary person completing any part of the analysis of this project, I thought this would nonetheless be a good opportunity to present locally the program and initial results that have been completed by many members of the OSU astronomy community and other collaborators from the STORM Project.

# Far-IR temperature-insensitive metallicity diagnostics

7/28/15
Kevin Croxall (OSU Astronomy)

With the advent of the latest generation of NIR spectrographs, new diagnostics of the physical properties of high-redshift galaxies have now become attainable. These instruments have facilitated high-quality measurement of multiple nebular emission lines for 100s of high-z galaxies. The first results from large surveys have shown there to be important discrepancies between the physical conditions and abundance patterns within high-z and local star-forming galaxies. In light of these new observations, a more sophisticated understanding of massive stellar evolution and photoionization modeling is required to interpret the data in a physically meaningful manner. I will discuss the use and usefulness of the FIR fine-structure lines in understanding the abundance patterns and physical conditions of ionized gas in local galaxies. Additionally, I will discuss their use in high-z star forming galaxies.

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