Risa H. Wechsler
A5085208759- Galaxies: Formation, Evolution, Phenomena
- Astronomy and Astrophysical Research
- Stellar, planetary, and galactic studies
- Cosmology and Gravitation Theories
- Gamma-ray bursts and supernovae
- Dark Matter and Cosmic Phenomena
- Adaptive optics and wavefront sensing
- Astrophysics and Cosmic Phenomena
- Scientific Research and Discoveries
- Remote Sensing in Agriculture
- CCD and CMOS Imaging Sensors
- Astronomical Observations and Instrumentation
- Radio Astronomy Observations and Technology
- Astrophysics and Star Formation Studies
- Impact of Light on Environment and Health
- Gaussian Processes and Bayesian Inference
- Astrophysical Phenomena and Observations
- Pulsars and Gravitational Waves Research
- History and Developments in Astronomy
- Computational Physics and Python Applications
- Plant Water Relations and Carbon Dynamics
- Geophysics and Gravity Measurements
- Spatial and Panel Data Analysis
- Statistical and numerical algorithms
- Advanced Vision and Imaging
SLAC National Accelerator Laboratory
2016-2025
Kavli Institute for Particle Astrophysics and Cosmology
2016-2025
Stanford University
2016-2025
Menlo School
2013-2025
Ludwig-Maximilians-Universität München
2024
Oak Ridge National Laboratory
2024
Lancaster University
2024
Centre National de la Recherche Scientifique
2024
Aix-Marseille Université
2024
Austin Peay State University
2024
We present a robust method to constrain average galaxy star formation rates, histories, and the intracluster light as function of halo mass. Our results are consistent with observed stellar mass functions, specific cosmic rates from z=0 z=8. consider effects wide range uncertainties on our results, including those affecting masses, at heart analysis. As they relevant method, we also new calibrations dark matter function, accretion halo-subhalo merger out provide compilations rates; more...
The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) is designed to document the first third of galactic evolution, over approximate redshift (z) range 8--1.5. It will image >250,000 distant galaxies using three separate cameras on Hubble Space Telescope, from mid-ultraviolet near-infrared, and find measure Type Ia supernovae at z>1.5 test their accuracy as standardizable candles for cosmology. Five premier multi-wavelength sky regions are selected, each with...
We present a new algorithm for identifying dark matter halos, substructure, and tidal features. The approach is based on adaptive hierarchical refinement of friends-of-friends groups in six phase-space dimensions one time dimension, which allows robust (grid-independent, shape-independent, noise-resilient) tracking substructure; as such, it named Rockstar (Robust Overdensity Calculation using K-Space Topologically Adaptive Refinement). Our method massively parallel (up to 10^5 CPUs) runs the...
We study the relation between density profiles of dark matter halos and their mass assembly histories using a statistical sample in high-resolution N-body simulation ΛCDM cosmology. For each halo at z = 0, we identify its merger history tree determine concentration parameters cvir for all progenitors, thus providing structural halo. fit accretion by universal function with one parameter, formation epoch ac, defined when log rate d M/d falls below critical value S. find that late-forming...
We present a method to flexibly and self-consistently determine individual galaxies' star formation rates (SFRs) from their host haloes' potential well depths, assembly histories, redshifts. The is constrained by observed stellar mass functions, SFRs (specific cosmic), quenched fractions, UV luminosity UV-SM relations, IRX-UV auto- cross-correlation functions (including star-forming subsamples), quenching dependence on environment; each observable reproduced over the full redshift range...
We conduct a comprehensive analysis of the relationship between central galaxies and their host dark matter halos, as characterized by stellar mass-halo mass (SM-HM) relation, with rigorous consideration uncertainties. Our focuses on results from abundance matching technique, which assumes that every halo or subhalo above specific threshold hosts one galaxy. discuss quantitative effects uncertainties in observed galaxy functions (GSMFs) (including estimates counting uncertainties), cosmology...
We analyze the halo occupation distribution (HOD), probability for a of mass M to host number subhalos N, and two-point correlation function galaxy-size dark matter halos using high-resolution dissipationless simulations concordance flat LCDM model. The samples include both subhalos, distinct gravitationally-bound within virialized regions larger systems. find that first moment HOD, (M), has complicated shape consisting step, shoulder, power law high-mass tail. HOD can be described by...
In our modern understanding of galaxy formation, every forms within a dark matter halo. The formation and growth galaxies over time is connected to the halos in which they form. advent large surveys as well high-resolution cosmological simulations has provided new window into statistical relationship between its evolution. Here, we define this galaxy–halo connection multivariate distribution halo properties that can be derived from observations simulations. This provides key test physical...
We describe redMaPPer, a new red sequence cluster finder specifically designed to make optimal use of ongoing and near-future large photometric surveys. The algorithm has multiple attractive features: (1) it can iteratively self-train the model based on minimal spectroscopic training sample, an important feature for high-redshift (2) It handle complex masks with varying depth. (3) produces cluster-appropriate random points enable large-scale structure studies. (4) All clusters are assigned...
We use 26×106 galaxies from the Dark Energy Survey (DES) Year 1 shape catalogs over 1321 deg2 of sky to produce most significant measurement cosmic shear in a galaxy survey date. constrain cosmological parameters both flat ΛCDM and wCDM models, while also varying neutrino mass density. These results are shown be robust using two independent catalogs, photo-z calibration methods, analysis pipelines blind analysis. find 3.5% fractional uncertainty on σ8(Ωm/0.3)0.5=0.782+0.027−0.027 at 68%...
We employ high-resolution dissipationless simulations of the concordance ΛCDM cosmology (Ω0 = 1 - ΩΛ 0.3, h 0.7, σ8 0.9) to model observed luminosity dependence and evolution galaxy clustering through most age universe, from z ~ 5 0. use a simple, nonparametric model, which monotonically relates luminosities maximum circular velocity dark matter halos (Vmax) by preserving function in order match with galaxies. The novel feature is at time accretion, V, for subhalos, located within virial...
We present a catalog of galaxy clusters selected using the maxBCG redsequence method from Sloan Digital Sky Survey photometric data. This includes 13,823 with velocity dispersions greater than 400 km/s, and is largest cluster assembled to date. They are in an approximately volume-limited way 0.5 Gpc^3 region covering 7500 square degrees sky between redshifts 0.1 0.3. (ABRIGDED)
We present a new algorithm for generating merger trees and halo catalogs which explicitly ensures consistency of properties (mass, position, velocity) across timesteps. Our has demonstrated the ability to improve both completeness (through detecting inserting otherwise missing halos) purity removing spurious objects) catalogs. In addition, our method is able robustly measure self-consistency finders; it first directly uncertainties in positions, velocities, mass function given finder based...
Using six high resolution dissipationless simulations with a varying box size in flat LCDM universe, we study the mass and redshift dependence of dark matter halo shapes for M_vir = 9.0e11 - 2.0e14, over range z=0-3, two values sigma_8=0.75 0.9. Remarkably, find that redshift, mass, sigma_8 mean smallest-to-largest axis ratio halos is well described by simple power-law relation (0.54 +- 0.02)(M_vir/M_*)^(-0.050 0.003), where s measured at 0.3 R_vir z dependences are governed characteristic...
We investigate the dependence of dark matter halo clustering on formation time, density profile concentration, and subhalo occupation number, using high-resolution numerical simulations a LCDM cosmology. confirm results that is function this trend depends mass. For first we show unequivocally concentration bias mass, redshift can be accurately parameterized in simple way: b(c,M|z) = b(M|z) b(c|M/M*). The scaling between changes sign with value M/M*: high (early forming) objects cluster more...
We report the discovery of eight new ultra-faint dwarf galaxy candidates in second year optical imaging data from Dark Energy Survey (DES). Six these are detected at high confidence, while two lower-confidence identified regions non-uniform survey coverage. The stellar systems found by three independent automated search techniques and as overdensities stars, consistent with isochrone luminosity function an old metal-poor simple population. faint (Mv > -4.7 mag) span a range physical sizes...
A simple, observationally motivated model is presented for understanding how halo masses, galaxy stellar and star formation rates are related, these relations evolve with time. The relation between mass determined by matching the observed spatial abundance of galaxies to expected halos at multiple epochs, i.e., more massive assigned each epoch. This "abundance matching" technique has been shown previously reproduce luminosity scale dependence clustering over a range epochs. Halos different...
Using data from the COSMOS survey, we perform first joint analysis of galaxy-galaxy weak lensing, galaxy spatial clustering, and number densities. Carefully accounting for sample variance scatter between stellar halo mass, model all three observables simultaneously using a novel self-consistent theoretical framework. Our results provide strong constraints on shape redshift evolution stellar-to-halo mass relation (SHMR) z=0.2 to z=1. At low find that scales as Mh M*^0.46 this scaling does not...
We report the discovery of eight new Milky Way companions in optical imaging data collected during first year Dark Energy Survey (DES). Each system is identified as a statistically significant over-density individual stars consistent with expected isochrone and luminosity function an old metal-poor stellar population. The objects span wide range absolute magnitudes (MV from to ), physical sizes (), heliocentric distances (). Based on low surface brightnesses, large sizes, and/or...
We provide new constraints on the connection between galaxies in local universe, identified by Sloan Digital Sky Survey (SDSS), and dark matter halos their constituent substructures $\Lambda$CDM model using WMAP7 cosmological parameters. Predictions for abundance clustering properties of halos, relationship hosts substructures, are based a high-resolution simulation, Bolshoi simulation. associate with subhalos subhalo matching, performing comprehensive analysis which investigates underlying...
We use the abundance and weak-lensing mass measurements of Sloan Digital Sky Survey maxBCG cluster catalog to simultaneously constrain cosmology richness–mass relation clusters. Assuming a flat ΛCDM cosmology, we find σ8(Ωm/0.25)0.41 = 0.832 ± 0.033 after marginalization over all systematics. In common with previous studies, our error budget is dominated by systematic uncertainties, primary two being absolute scale masses clusters, uncertainty in scatter relation. Our constraints are fully...
ABSTRACT We search for excess γ -ray emission coincident with the positions of confirmed and candidate Milky Way satellite galaxies using six years data from Fermi Large Area Telescope (LAT). Our sample 45 stellar systems includes 28 kinematically dark-matter-dominated dwarf spheroidal (dSphs) 17 recently discovered that have photometric characteristics consistent population known dSphs. For each these targets, relative predicted flux due to dark matter annihilation is taken kinematic...
ABSTRACT We describe updates to the redMaPPer algorithm, a photometric red-sequence cluster finder specifically designed for large surveys. The updated algorithm is applied of Science Verification (SV) data from Dark Energy Survey (DES), and Sloan Digital Sky (SDSS) DR8 set. DES SV catalog locally volume limited contains 786 clusters with richness (roughly equivalent ) . consists 26,311 , sharply increasing threshold as function redshift performance both catalogs shown be excellent,...
This work, together with its companion paper, Secco and Samuroff et al. (2021), presents the Dark Energy Survey Year 3 cosmic shear measurements cosmological constraints based on an analysis of over 100 million source galaxies. With data spanning 4143 deg$^2$ sky, divided into four redshift bins, we produce highest significance measurement to date, a signal-to-noise 40. We conduct blind in context $\Lambda$CDM model find 3% constraint clustering amplitude, $S_8\equiv \sigma_8 (\Omega_{\rm...
We present a large catalog of optically selected galaxy clusters from the application new Gaussian Mixture Brightest Cluster Galaxy (GMBCG) algorithm to SDSS Data Release 7 data. The detects by identifying red-sequence plus brightest cluster (BCG) feature, which is unique for and does not exist among field galaxies. Red-sequence clustering in color space detected using an Error Corrected Model. run GMBCG on 8240 deg2 photometric data DR7 assemble largest ever optical catalog, consisting over...