Andrew R. Zentner - University Pitt

Andrew R. Zentner
Are you Andrew R. Zentner?

Claim your profile, edit publications, add additional information:

Contact Details

Name
Andrew R. Zentner
Affiliation
University Pitt
City
Pittsburgh
Country
United States

Pubs By Year

External Links

Pub Categories

 
Cosmology and Nongalactic Astrophysics (41)
 
Astrophysics of Galaxies (15)
 
High Energy Physics - Phenomenology (8)
 
High Energy Astrophysical Phenomena (4)
 
Astrophysics (2)
 
Solar and Stellar Astrophysics (2)
 
Instrumentation and Methods for Astrophysics (2)
 
Earth and Planetary Astrophysics (1)
 
High Energy Physics - Experiment (1)

Publications Authored By Andrew R. Zentner

Galaxy clustering on small scales is significantly under-predicted by sub-halo abundance matching (SHAM) models that populate (sub-)haloes with galaxies based on peak halo mass, $M_{\rm peak}$. SHAM models based on the peak maximum circular velocity, $V_{\rm peak}$, have had much better success. The primary reason $M_{\rm peak}$ based models fail is the relatively low abundance of satellite galaxies produced in these models compared to those based on $V_{\rm peak}$. Read More

Determining the positions of halo centres in large-scale structure surveys is crucial for many cosmological studies. A common assumption is that halo centres correspond to the location of their brightest member galaxies. In this paper, we study the dynamics of brightest galaxies with respect to other halo members in the Sloan Digital Sky Survey DR7. Read More

2017May
Affiliations: 1U Pittsburgh/PITT PACC, 2U Pittsburgh/PITT PACC, 3U Pittsburgh/PITT PACC, 4RIT/CCRG, 5Yale, 6CfA/Harvard, 7Yale, 8U Pittsburgh/PITT PACC, 9Yale

Dark matter halo clustering depends not only on halo mass, but also on other properties such as concentration and shape. This phenomenon is known broadly as assembly bias. We explore the dependence of assembly bias on halo definition, parametrized by spherical overdensity parameter, $\Delta$. Read More

2017May
Affiliations: 1U Pittsburgh/PITT PACC, 2U Pittsburgh/PITT PACC, 3KIPAC/Stanford/SLAC

Secondary halo bias, commonly known as "assembly bias," is the dependence of halo clustering on a halo property other than mass. This prediction of the Lambda-Cold Dark Matter cosmology is essential to modelling the galaxy distribution to high precision and interpreting clustering measurements. As the name suggests, different manifestations of secondary halo bias have been thought to originate from halo assembly histories. Read More

A strong correlation has been measured between the observed centripetal accelerations in galaxies and the accelerations implied by the baryonic components of galaxies. This empirical radial acceleration relation must be accounted for in any viable model of galaxy formation. We measure and compare the radial accelerations contributed by baryons and by dark matter in disk galaxies in the MassiveBlack-II hydrodynamic galaxy formation simulation. Read More

We constrain the newly-introduced decorated Halo Occupation Distribution (HOD) model using SDSS DR7 measurements of projected galaxy clustering or r-band luminosity threshold samples. The decorated HOD is a model for the galaxy-halo connection that augments the HOD by allowing for the possibility of galaxy assembly bias: galaxy luminosity may be correlated with dark matter halo properties besides mass, Mvir. We demonstrate that it is not possible to rule out galaxy assembly bias using DR7 measurements of galaxy clustering alone. Read More

We present the first stable release of Halotools (v0.2), a community-driven Python package designed to build and test models of the galaxy-halo connection. Halotools provides a modular platform for creating mock universes of galaxies starting from a catalog of dark matter halos obtained from a cosmological simulation. Read More

The connection between galaxies and dark matter halos is often inferred from data using probabilistic models, such as the Halo Occupation Distribution (HOD). Conventional HOD formulations assume that only halo mass governs the galaxy-halo connection. Violations of this assumption, known as galaxy assembly bias, threaten the HOD program. Read More

Traditional cosmological inference using Type Ia supernovae (SNeIa) have used stretch- and color-corrected fits of SN Ia light curves and assumed a resulting fiducial mean and symmetric intrinsic dispersion for the resulting relative luminosity. As systematics become the main contributors to the error budget, it has become imperative to expand supernova cosmology analyses to include a more general likelihood to model systematics to remove biases with losses in precision. To illustrate an example likelihood analysis, we use a simple model of two populations with a relative luminosity shift, independent intrinsic dispersions, and linear redshift evolution of the relative fraction of each population. Read More

We use cosmological simulations to identify dark matter subhalo host candidates of the Fornax dwarf spheroidal galaxy using the stellar kinematic properties of Fornax. We consider cold dark matter (CDM), warm dark matter (WDM), and decaying dark matter (DDM) simulations for our models of structure formation. The subhalo candidates in CDM typically have smaller mass and higher concentrations at z = 0 than the corresponding candidates in WDM and DDM. Read More

We use subhalo abundance matching (SHAM) to model the stellar mass function (SMF) and clustering of the Baryon Oscillation Spectroscopic Survey (BOSS) "CMASS" sample at $z\sim0.5$. We introduce a novel method which accounts for the stellar mass incompleteness of CMASS as a function of redshift, and produce CMASS mock catalogs which include selection effects, reproduce the overall SMF, the projected two-point correlation function $w_{\rm p}$, the CMASS $dn/dz$, and are made publicly available. Read More

White Dwarfs (WD) capture Dark Matter (DM) as they orbit within their host halos. These captured particles may subsequently annihilate, heating the stellar core and preventing the WD from cooling. The potential wells of WDs are considerably deeper and core temperatures significantly cooler than those of main sequence stars. Read More

We present a set of N-body simulations of a class of models in which an unstable dark matter particle decays into a stable non-interacting dark matter particle, with decay lifetime comparable to the Hubble time. We study the effects of the kinematic recoil velocity received by the stable dark matter on the structures of dark matter halos ranging from galaxy-cluster to Milky Way mass scales. For Milky Way-mass halos, we use high-resolution, zoom-in simulations to explore the effects of decays on Galactic substructure. Read More

Systematic uncertainties that have been subdominant in past large-scale structure (LSS) surveys are likely to exceed statistical uncertainties of current and future LSS data sets, potentially limiting the extraction of cosmological information. Here we present a general framework (PCA marginalization) to consistently incorporate systematic effects into a likelihood analysis. This technique naturally accounts for degeneracies between nuisance parameters and can substantially reduce the dimension of the parameter space that needs to be sampled. Read More

We examine the importance of baryonic feedback effects on the matter power spectrum on small scales, and the implications for the precise measurement of neutrino masses through gravitational weak lensing. Planned large galaxy surveys such as the Large Synoptic Sky Telescope (LSST) and Euclid are expected to measure the sum of neutrino masses to extremely high precision, sufficient to detect non-zero neutrino masses even in the minimal mass normal hierarchy. We show that weak lensing of galaxies while being a very good probe of neutrino masses, is extremely sensitive to baryonic feedback processes. Read More

In this paper, we test the age matching hypothesis that the star formation rate (SFR) of a galaxy of fixed stellar mass is determined by its dark matter halo formation history, and as such, that more quiescent galaxies reside in older halos. This simple model has been remarkably successful at predicting color-based galaxy statistics at low redshift as measured in the Sloan Digital Sky Survey (SDSS). To further test this method with observations, we present new SDSS measurements of the galaxy two-point correlation function and galaxy-galaxy lensing as a function of stellar mass and SFR, separated into quenched and star-forming galaxy samples. Read More

It is common practice for methods that use galaxy clustering to constrain the galaxy-halo relationship, such as the halo occupation distribution (HOD) and/or conditional luminosity function (CLF), to assume that halo mass alone suffices to determine a halo's resident galaxy population. Yet, the clustering strength of cold dark matter halos depends upon halo properties in addition to mass, such as formation time, an effect referred to as assembly bias. If galaxy characteristics are correlated with any of these auxiliary halo properties, the basic assumption of HOD/CLF methods is violated. Read More

The age matching model has recently been shown to predict correctly the luminosity L and g-r color of galaxies residing within dark matter halos. The central tenet of the model is intuitive: older halos tend to host galaxies with older stellar populations. In this paper, we demonstrate that age matching also correctly predicts the g-r color trends exhibited in a wide variety of statistics of the galaxy distribution for stellar mass M* threshold samples. Read More

We present an analysis of high-resolution N-body simulations of decaying dark matter cosmologies focusing on the statistical properties of the transmitted Lyman-alpha forest flux in the high-redshift intergalactic medium. In this type of model a dark matter particle decays into a slightly less massive stable dark matter daughter particle and a comparably light particle. The small mass splitting provides a non-relativistic kick velocity V_k to the daughter particle resulting in free-streaming and subsequent damping of small-scale density fluctuations. Read More

We have devised a method to select galaxies that are isolated in their dark matter halo (N=1 systems) and galaxies that reside in a group of exactly two (N=2 systems). Our N=2 systems are widely-separated (up to $\sim$\,200\,$h^{-1}$\,kpc), where close galaxy-galaxy interactions are not dominant. We apply our selection criteria to two volume-limited samples of galaxies from SDSS DR6 with $M_{r}-5 \log_{10} h \leq$ -19 and -20 to study the effects of the environment of very sparse groups on galaxy colour. Read More

2012Dec
Affiliations: 1University of Pittsburgh, 2Leiden Observatory, 3FNAL/UChicago, 4UPenn, 5UPenn, 6FNAL

One of the most pernicious theoretical systematics facing upcoming gravitational lensing surveys is the uncertainty introduced by the effects of baryons on the power spectrum of the convergence field. One method that has been proposed to account for these effects is to allow several additional parameters (that characterize dark matter halos) to vary and to fit lensing data to these halo parameters concurrently with the standard set of cosmological parameters. We test this method. Read More

We construct mock catalogs of galaxy groups using subhalo abundance matching (SHAM) and undertake several new tests of the SHAM prescription for the galaxy-dark matter connection. All SHAM models we studied exhibit significant tension with galaxy groups observed in the Sloan Digital Sky Survey (SDSS). The SHAM prediction for the field galaxy luminosity function (LF) is systematically too dim, and the group galaxy LF systematically too bright, regardless of the details of the SHAM prescription. Read More

Recent kinematical constraints on the internal densities of the Milky Way's dwarf satellites have revealed a discrepancy with the subhalo populations of simulated Galaxy-scale halos in the standard CDM model of hierarchical structure formation. This has been dubbed the "too big to fail" problem, with reference to the improbability of large and invisible companions existing in the Galactic environment. In this paper, we argue that both the Milky Way observations and simulated subhalos are consistent with the predictions of the standard model for structure formation. Read More

We investigate the potential to improve optical tracers of cluster mass by exploiting measurements of the magnitude gap, m12, defined as the difference between the r-band absolute magnitude of the two brightest cluster members. We find that in a mock sample of galaxy groups and clusters constructed from the Bolshoi simulation, the scatter about the mass-richness relation decreases by 15-20% when magnitude gap information is included. A similar trend is evident in a volume-limited, spectroscopic sample of galaxy groups observed in the Sloan Digital Sky Survey (SDSS). Read More

We analyze self-consistent N-body simulations of the Milky Way disk and the ongoing disruption of the Sagittarius dwarf satellite to study the effect of Sagittarius tidal debris on dark matter detection experiments. In agreement with significant previous work, we reiterate that the standard halo model is insufficient to describe the non-Maxwellian velocity distribution of the Milky Way halo in our equilibrium halo-only and halo/galaxy models, and offer suggestions for correcting for this discrepancy. More importantly, we emphasize that the dark matter component of the leading tidal arm of the Sagittarius dwarf is significantly more extended than the stellar component of the arm, since the dark matter and stellar streams are not necessarily coaxial and may be offset by several kpc at the point at which they impact the Galactic disk. Read More

We introduce a new technique that uses galaxy clustering to constrain how satellite galaxies lose stellar mass and contribute to the diffuse "intrahalo light" (IHL). We implement two models that relate satellite galaxy stellar mass loss to the detailed knowledge of subhalo dark matter mass loss. Model 1 assumes that the fractional stellar mass loss of a galaxy is proportional to the fractional amount of dark matter mass loss of its subhalo. Read More

In this paper we explore the effect of decaying dark matter (DDM) on large-scale structure and possible constraints from galaxy imaging surveys. DDM models have been studied, in part, as a way to address apparent discrepancies between the predictions of standard cold dark matter models and observations of galactic structure. Our study is aimed at developing independent constraints on these models. Read More

Simulations of cluster formation have demonstrated that condensation of baryons into central galaxies during cluster formation can drive the shape of the gas distribution in galaxy clusters significantly rounder, even at radii as large as half of the virial radius. However, such simulations generally predict stellar fractions within cluster virial radii that are ~2 to 3 times larger than the stellar masses deduced from observations. In this work we compare ellipticity profiles of clusters simulated with and without baryonic cooling to the cluster ellipticity profiles derived from Chandra and ROSAT observations in an effort to constrain the fraction of gas that cools and condenses into the central galaxies within clusters. Read More

We perform a pixel-by-pixel analysis of 467 galaxies in the GOODS-VIMOS survey to study systematic effects in extracting properties of stellar populations (age, dust, metallicity and SFR) from pixel colors using the pixel-z method. The systematics studied include the effect of the input stellar population synthesis model, passband limitations and differences between individual SED fits to pixels and global SED-fitting to a galaxy's colors. We find that with optical-only colors, the systematic errors due to differences among the models are well constrained. Read More

Forthcoming projects such as DES, LSST, WFIRST, and Euclid aim to measure weak lensing shear correlations with unprecedented precision, constraining the dark energy equation of state at the percent level. Reliance on photometrically-determined redshifts constitutes a major source of uncertainty for these surveys. Additionally, interpreting the weak lensing signal requires a detailed understanding of the nonlinear physics of gravitational collapse. Read More

We study energy transport by asymmetric dark matter in the interiors of very low-mass stars and brown dwarfs. Our motivation is to explore astrophysical signatures of asymmetric dark matter, which otherwise may not be amenable to conventional indirect dark matter searches. In viable models, the additional cooling of very-low mass stellar cores can alter stellar properties. Read More

The cosmic microwave background (CMB) temperature distribution measured by the Wilkinson Microwave Anisotropy Probe (WMAP) exhibits anomalously low correlation at large angles. Quantifying the degree to which this feature in the temperature data is in conflict with standard Lambda-CDM cosmology is somewhat ambiguous because of the a posteriori nature of the observation. One physical mechanism that has been proposed as a possible explanation for the deficit in the large-angle temperature correlations is a suppression of primordial power on ~Gpc scales. Read More

We model the evolution of galaxy clustering through cosmic time to investigate the nature of the power-law shape of xi(r), the galaxy two-point correlation function. Departures from a power law are mainly governed by galaxy pair counts on small scales, subject to non-linear dynamics. We assume that galaxies reside within dark matter halos and subhalos and use a semi-analytic substructure evolution model to study subhalo populations within host halos. Read More

We explore the halo-to-halo variation of dark matter substructure in galaxy-sized dark matter halos, focusing on its implications for strongly gravitational lensed systems. We find that the median value for projected substructure mass fractions within projected radii of 3% of the host halo virial radius is approximately fsub ~ 0.25%, but that the variance is large with a 95-percentile range of 0 <= fsub <= 1%. Read More

The nature of the dark matter remains a mystery. The possibility of an unstable dark matter particle decaying to invisible daughter particles has been explored many times in the past few decades. Meanwhile, weak gravitational lensing shear has gained a lot of attention as a probe of dark energy. Read More

Environmental statistics provide a necessary means of comparing the properties of galaxies in different environments and a vital test of models of galaxy formation within the prevailing, hierarchical cosmological model. We explore counts-in-cylinders, a common statistic defined as the number of companions of a particular galaxy found within a given projected radius and redshift interval. Galaxy distributions with the same two-point correlation functions do not necessarily have the same companion count distributions. Read More

2010Aug
Affiliations: 1LANL, 2University of Pittsburgh, 3University of Pittsburgh, 4University of Pittsburgh

Upcoming imaging surveys such as the Large Synoptic Survey Telescope will repeatedly scan large areas of sky and have the potential to yield million-supernova catalogs. Type Ia supernovae are excellent standard candles and will provide distance measures that suffice to detect mean pairwise velocities of their host galaxies. We show that when combining these distance measures with photometric redshifts for either the supernovae or their host galaxies, the mean pairwise velocities of the host galaxies will provide a dark energy probe which is competitive with other widely discussed methods. Read More

We calculate the probability distribution function (PDF) of the expected annihilation luminosities of dark matter subhalos as a function of subhalo mass and distance from the Galactic center using a semi-analytical model of halo evolution. We find that the PDF of luminosities is relatively broad, exhibiting a spread of as much as an order of magnitude at fixed subhalo mass and halo-centric distance. The luminosity PDF allows for simple construction of mock samples of gamma-ray luminous subhalos and assessment of the variance in among predicted gamma-ray signals from dark matter annihilation. Read More

We present analysis of the three-dimensional shape of intracluster gas in clusters formed in cosmological simulations of the Lambda-CDM cosmology and compare it to the shape of dark matter distribution and the shape of the overall isopotential surfaces. We find that in simulations with radiative cooling, star formation and stellar feedback (CSF), intracluster gas outside the cluster core is more spherical compared to non-radiative (NR) simulations, while in the core the gas in the CSF runs is more triaxial and has a distinctly oblate shape. The latter reflects the ongoing cooling of gas, which settles into a thick oblate ellipsoid as it loses thermal energy. Read More

A goal of forthcoming imaging surveys is to use weak gravitational lensing shear measurements to constrain dark energy. We quantify the importance of uncalibrated photometric redshift outliers to the dark energy goals of forthcoming imaging surveys in a manner that does not assume any particular photometric redshift technique or template. In so doing, we provide an approximate blueprint for computing the influence of specific outlier populations on dark energy constraints. Read More

2009Dec
Authors: LSST Science Collaboration, Paul A. Abell1, Julius Allison2, Scott F. Anderson3, John R. Andrew4, J. Roger P. Angel5, Lee Armus6, David Arnett7, S. J. Asztalos8, Tim S. Axelrod9, Stephen Bailey10, D. R. Ballantyne11, Justin R. Bankert12, Wayne A. Barkhouse13, Jeffrey D. Barr14, L. Felipe Barrientos15, Aaron J. Barth16, James G. Bartlett17, Andrew C. Becker18, Jacek Becla19, Timothy C. Beers20, Joseph P. Bernstein21, Rahul Biswas22, Michael R. Blanton23, Joshua S. Bloom24, John J. Bochanski25, Pat Boeshaar26, Kirk D. Borne27, Marusa Bradac28, W. N. Brandt29, Carrie R. Bridge30, Michael E. Brown31, Robert J. Brunner32, James S. Bullock33, Adam J. Burgasser34, James H. Burge35, David L. Burke36, Phillip A. Cargile37, Srinivasan Chandrasekharan38, George Chartas39, Steven R. Chesley40, You-Hua Chu41, David Cinabro42, Mark W. Claire43, Charles F. Claver44, Douglas Clowe45, A. J. Connolly46, Kem H. Cook47, Jeff Cooke48, Asantha Cooray49, Kevin R. Covey50, Christopher S. Culliton51, Roelof de Jong52, Willem H. de Vries53, Victor P. Debattista54, Francisco Delgado55, Ian P. Dell'Antonio56, Saurav Dhital57, Rosanne Di Stefano58, Mark Dickinson59, Benjamin Dilday60, S. G. Djorgovski61, Gregory Dobler62, Ciro Donalek63, Gregory Dubois-Felsmann64, Josef Durech65, Ardis Eliasdottir66, Michael Eracleous67, Laurent Eyer68, Emilio E. Falco69, Xiaohui Fan70, Christopher D. Fassnacht71, Harry C. Ferguson72, Yanga R. Fernandez73, Brian D. Fields74, Douglas Finkbeiner75, Eduardo E. Figueroa76, Derek B. Fox77, Harold Francke78, James S. Frank79, Josh Frieman80, Sebastien Fromenteau81, Muhammad Furqan82, Gaspar Galaz83, A. Gal-Yam84, Peter Garnavich85, Eric Gawiser86, John Geary87, Perry Gee88, Robert R. Gibson89, Kirk Gilmore90, Emily A. Grace91, Richard F. Green92, William J. Gressler93, Carl J. Grillmair94, Salman Habib95, J. S. Haggerty96, Mario Hamuy97, Alan W. Harris98, Suzanne L. Hawley99, Alan F. Heavens100, Leslie Hebb101, Todd J. Henry102, Edward Hileman103, Eric J. Hilton104, Keri Hoadley105, J. B. Holberg106, Matt J. Holman107, Steve B. Howell108, Leopoldo Infante109, Zeljko Ivezic110, Suzanne H. Jacoby111, Bhuvnesh Jain112, R113, Jedicke114, M. James Jee115, J. Garrett Jernigan116, Saurabh W. Jha117, Kathryn V. Johnston118, R. Lynne Jones119, Mario Juric120, Mikko Kaasalainen121, Styliani122, Kafka, Steven M. Kahn, Nathan A. Kaib, Jason Kalirai, Jeff Kantor, Mansi M. Kasliwal, Charles R. Keeton, Richard Kessler, Zoran Knezevic, Adam Kowalski, Victor L. Krabbendam, K. Simon Krughoff, Shrinivas Kulkarni, Stephen Kuhlman, Mark Lacy, Sebastien Lepine, Ming Liang, Amy Lien, Paulina Lira, Knox S. Long, Suzanne Lorenz, Jennifer M. Lotz, R. H. Lupton, Julie Lutz, Lucas M. Macri, Ashish A. Mahabal, Rachel Mandelbaum, Phil Marshall, Morgan May, Peregrine M. McGehee, Brian T. Meadows, Alan Meert, Andrea Milani, Christopher J. Miller, Michelle Miller, David Mills, Dante Minniti, David Monet, Anjum S. Mukadam, Ehud Nakar, Douglas R. Neill, Jeffrey A. Newman, Sergei Nikolaev, Martin Nordby, Paul O'Connor, Masamune Oguri, John Oliver, Scot S. Olivier, Julia K. Olsen, Knut Olsen, Edward W. Olszewski, Hakeem Oluseyi, Nelson D. Padilla, Alex Parker, Joshua Pepper, John R. Peterson, Catherine Petry, Philip A. Pinto, James L. Pizagno, Bogdan Popescu, Andrej Prsa, Veljko Radcka, M. Jordan Raddick, Andrew Rasmussen, Arne Rau, Jeonghee Rho, James E. Rhoads, Gordon T. Richards, Stephen T. Ridgway, Brant E. Robertson, Rok Roskar, Abhijit Saha, Ata Sarajedini, Evan Scannapieco, Terry Schalk, Rafe Schindler, Samuel Schmidt, Sarah Schmidt, Donald P. Schneider, German Schumacher, Ryan Scranton, Jacques Sebag, Lynn G. Seppala, Ohad Shemmer, Joshua D. Simon, M. Sivertz, Howard A. Smith, J. Allyn Smith, Nathan Smith, Anna H. Spitz, Adam Stanford, Keivan G. Stassun, Jay Strader, Michael A. Strauss, Christopher W. Stubbs, Donald W. Sweeney, Alex Szalay, Paula Szkody, Masahiro Takada, Paul Thorman, David E. Trilling, Virginia Trimble, Anthony Tyson, Richard Van Berg, Daniel Vanden Berk, Jake VanderPlas, Licia Verde, Bojan Vrsnak, Lucianne M. Walkowicz, Benjamin D. Wandelt, Sheng Wang, Yun Wang, Michael Warner, Risa H. Wechsler, Andrew A. West, Oliver Wiecha, Benjamin F. Williams, Beth Willman, David Wittman, Sidney C. Wolff, W. Michael Wood-Vasey, Przemek Wozniak, Patrick Young, Andrew Zentner, Hu Zhan
Affiliations: 1Stella, 2Stella, 3Stella, 4Stella, 5Stella, 6Stella, 7Stella, 8Stella, 9Stella, 10Stella, 11Stella, 12Stella, 13Stella, 14Stella, 15Stella, 16Stella, 17Stella, 18Stella, 19Stella, 20Stella, 21Stella, 22Stella, 23Stella, 24Stella, 25Stella, 26Stella, 27Stella, 28Stella, 29Stella, 30Stella, 31Stella, 32Stella, 33Stella, 34Stella, 35Stella, 36Stella, 37Stella, 38Stella, 39Stella, 40Stella, 41Stella, 42Stella, 43Stella, 44Stella, 45Stella, 46Stella, 47Stella, 48Stella, 49Stella, 50Stella, 51Stella, 52Stella, 53Stella, 54Stella, 55Stella, 56Stella, 57Stella, 58Stella, 59Stella, 60Stella, 61Stella, 62Stella, 63Stella, 64Stella, 65Stella, 66Stella, 67Stella, 68Stella, 69Stella, 70Stella, 71Stella, 72Stella, 73Stella, 74Stella, 75Stella, 76Stella, 77Stella, 78Stella, 79Stella, 80Stella, 81Stella, 82Stella, 83Stella, 84Stella, 85Stella, 86Stella, 87Stella, 88Stella, 89Stella, 90Stella, 91Stella, 92Stella, 93Stella, 94Stella, 95Stella, 96Stella, 97Stella, 98Stella, 99Stella, 100Stella, 101Stella, 102Stella, 103Stella, 104Stella, 105Stella, 106Stella, 107Stella, 108Stella, 109Stella, 110Stella, 111Stella, 112Stella, 113Stella, 114Stella, 115Stella, 116Stella, 117Stella, 118Stella, 119Stella, 120Stella, 121Stella, 122Stella

A survey that can cover the sky in optical bands over wide fields to faint magnitudes with a fast cadence will enable many of the exciting science opportunities of the next decade. The Large Synoptic Survey Telescope (LSST) will have an effective aperture of 6.7 meters and an imaging camera with field of view of 9. Read More

2009Oct
Affiliations: 1KIPAC, Stanford University, 2University of Pittsburgh, 3KIPAC, Stanford University

We study the impact of theoretical uncertainty in the dark matter halo mass function and halo bias on dark energy constraints from imminent galaxy cluster surveys. We find that for an optical cluster survey like the Dark Energy Survey, the accuracy required on the predicted halo mass function to make it an insignificant source of error on dark energy parameters is ~ 1%. The analogous requirement on the predicted halo bias is less stringent (~ 5%), particularly if the observable-mass distribution can be well constrained by other means. Read More

A potential flux of high-energy neutrinos from the annihilation of dark matter particles trapped within the Sun has been exploited to place indirect limits on particle dark matter. In most models, the dark matter interacts weakly, but the possibility of a dark matter particle with a large cross section for elastic scattering with itself has been proposed in several contexts. I study the consequences of such dark matter self-interactions for the high-energy neutrino flux from annihilation within the Sun. Read More

The formation and evolution of Black Holes inevitably affects the distribution of dark and baryonic matter in the neighborhood of the Black Hole. These effects may be particularly relevant around Supermassive and Intermediate Mass Black Holes (IMBHs), the formation of which can lead to large Dark Matter overdensities, called {\em spikes} and {\em mini-spikes} respectively. Despite being larger and more dense, spikes evolve at the very centers of galactic halos, in regions where numerous dynamical effects tend to destroy them. Read More

Forthcoming projects such as the DES, a JDEM, and LSST, aim to measure weak lensing shear correlations with unprecedented accuracy. Weak lensing observables are sensitive to both the distance-redshift relation and the growth of structure in the Universe. If the cause of accelerated cosmic expansion is dark energy within general relativity (GR), both cosmic distances and structure growth are governed by the properties of dark energy. Read More

2009Feb
Affiliations: 1JPL/Caltech, 2Maryland, 3Caltech, 4IfA, 5UC Irvine, 6Bonn, 7Conceptual Analytics, 8JPL/Caltech, 9JPL/Caltech, 10CITA, 11UCSC, 12JPL/Caltech, 13CfA, 14CITA, 15UCSC, 16Caltech, 17UCD, 18STScI, 19CfA, 20IAP, 21CfA, 22UCSC, 23JPL/Caltech, 24UC Irvine, 25Rutgers, 26LAM/OAMP, 27Kapteyn, 28Brown, 29IAS, 30UCLA, 31JPL/Caltech, 32CfA, 33UCSC, 34UCSB, 35MPIA, 36Yale, 37UCSC, 38UCSC, 39JPL/Caltech, 40Carnegie, 41JPL/Caltech, 42Stanford, 43Waterloo, 44CfA, 45Heidelberg, 46Stanford, 47Pittsburgh

There is a vast menagerie of plausible candidates for the constituents of dark matter, both within and beyond extensions of the Standard Model of particle physics. Each of these candidates may have scattering (and other) cross section properties that are consistent with the dark matter abundance, BBN, and the most scales in the matter power spectrum; but which may have vastly different behavior at sub-galactic "cutoff" scales, below which dark matter density fluctuations are smoothed out. The only way to quantitatively measure the power spectrum behavior at sub-galactic scales at distances beyond the local universe, and indeed over cosmic time, is through probes available in multiply imaged strong gravitational lenses. Read More

(Abridged) We perform dissipationless N-body simulations to elucidate the dynamical response of thin disks to bombardment by cold dark matter (CDM) substructure. Our method combines (1) cosmological simulations of the formation of Milky Way (MW)-sized CDM halos to derive the properties of substructure and (2) controlled numerical experiments of consecutive subhalo impacts onto an initially-thin, fully-formed MW type disk galaxy. The present study is the first to account for the evolution of satellite populations over cosmic time in such an investigation of disk structure. Read More

The detection of byproducts from particle annihilations in galactic halos would provide important information about the nature of the dark matter. Observational evidence for a local excess of high-energy positrons has motivated recent models with an additional interaction between dark matter particles that can result in a Sommerfeld enhancement to the cross section for annihilation. In such models, the cross section becomes velocity-dependent and may enhance the dark matter annihilation rate in the solar neighborhood relative to the rate in the early universe sufficiently to source observed fluxes of high-energy positrons. Read More

2008Dec
Affiliations: 1KICP/UChicago, 2KICP/UChicago, 3KICP/UChicago/BCCP/UCB, 4UPitt
Category: Astrophysics

Our heuristic understanding of the abundance of dark matter halos centers around the concept of a density threshold, or "barrier", for gravitational collapse. If one adopts the ansatz that regions of the linearly evolved density field smoothed on mass scale M with an overdensity that exceeds the barrier will undergo gravitational collapse into halos of mass M, the corresponding abundance of such halos can be estimated simply as a fraction of the mass density satisfying the collapse criterion divided by the mass M. The key ingredient of this ansatz is therefore the functional form of the collapse barrier as a function of mass M or, equivalently, of the variance sigma^2(M). Read More

2008Dec
Affiliations: 1University of Pittsburgh, 2University of Pittsburgh
Category: Astrophysics

We study the utility of a large sample of type Ia supernovae that might be observed in an imaging survey that rapidly scans a large fraction of the sky for constraining dark energy. We consider information from the traditional luminosity distance test as well as the spread in SNeIa fluxes at fixed redshift induced by gravitational lensing. We include a treatment of photometric redshift uncertainties in our analysis. Read More