A5024380456- Galaxies: Formation, Evolution, Phenomena
- Astronomy and Astrophysical Research
- Stellar, planetary, and galactic studies
- Cosmology and Gravitation Theories
- Dark Matter and Cosmic Phenomena
- Gamma-ray bursts and supernovae
- Scientific Research and Discoveries
- Adaptive optics and wavefront sensing
- Astrophysics and Cosmic Phenomena
- Pulsars and Gravitational Waves Research
- Astrophysics and Star Formation Studies
- Astronomical Observations and Instrumentation
- Astrophysical Phenomena and Observations
- History and Developments in Astronomy
- Impact of Light on Environment and Health
- Radio Astronomy Observations and Technology
- Geophysics and Gravity Measurements
- Remote Sensing in Agriculture
- Space Science and Extraterrestrial Life
- Computational Physics and Python Applications
- Astro and Planetary Science
- Black Holes and Theoretical Physics
- Quantum Electrodynamics and Casimir Effect
- CCD and CMOS Imaging Sensors
- Statistical and numerical algorithms
Perimeter Institute
2018-2024
University of Illinois Urbana-Champaign
2011-2018
Institute for Advanced Study
2003-2016
University of Zululand
2015-2016
Kavli Institute for the Physics and Mathematics of the Universe
2015-2016
The University of Tokyo
2015-2016
University of KwaZulu-Natal
2015-2016
Canadian Institute for Theoretical Astrophysics
2007-2011
University of Toronto
2006-2011
Campbell Collaboration
2009
We report on our search for microlensing towards the Large Magellanic Cloud (LMC). Analysis of 5.7 years photometry 11.9 million stars in LMC reveals 13 - 17 events. This is significantly more than $\sim$ 2 to 4 events expected from lensing by known stellar populations. The timescales ($\that$) range 34 230 days. estimate optical depth with $2 < \that 400$ days be 1.2 ^{+0.4}_ {-0.3} \ten{-7}$, an additional 20% 30% systematic error. spatial distribution mildly inconsistent LMC/LMC disk...
We study the effect of primordial non-Gaussianity on large-scale structure, focusing upon most massive virialized objects. Using analytic arguments and $N$-body simulations, we calculate mass function clustering dark matter halos across a range redshifts levels non-Gaussianity. propose simple fitting for valid entire our simulations. find pronounced effects halos, leading to strongly scale-dependent bias. This suggests that rare objects may provide sensitive probe very roughly estimate...
We devise a method to measure the abundance of satellite halos in gravitational lens galaxies and apply our sample seven systems. After using Monte Carlo simulations verify method, we find that substructure comprises fsat = 0.02 (median, 0.006 < 0.07 at 90% confidence) mass typical galaxies, excellent agreement with predictions cold dark matter (CDM) simulations. estimate characteristic critical radius for satellites 00001 b 0006 (90% confidence). For dn/dM ∝ M-1.8 (Mlow M Mhigh) function,...
Recent observations support the hypothesis that a large fraction of "short-hard" gamma-ray bursts (SHBs) are associated with compact binary inspiral. Since gravitational-wave (GW) measurements well-localized inspiraling binaries can measure absolute source distances, simultaneous observation binary's GWs and SHB would allow us to independently determine both its luminosity distance redshift. Such "standard siren" (the GW analog standard candle) provide an excellent probe relatively nearby...
ABSTRACT We study the abundance of substructure in matter density near galaxies using ALMA Science Verification observations strong lensing system SDP.81. present a method to measure subhalos around interferometric gravitational lenses. Using simulated we explore effects various systematics, including antenna phase errors and source priors, show how such may be measured or marginalized. apply our formalism find evidence for presence M = 10 8.96±0.12 ⊙ subhalo one images, with significance...
We use observations of ultrafaint dwarf (UFD) galaxies to constrain the particle mass ultralight dark matter. Potential fluctuations created by wave interference in virialized ``fuzzy'' matter (FDM) halos dynamically heat stellar orbits UFDs, some which exhibit velocity dispersions $\ensuremath{\lesssim}3\text{ }\text{ }\mathrm{km}/\mathrm{s}$ and sizes $\ensuremath{\lesssim}40\text{ }\mathrm{pc}$. Using simulations FDM halos, existing measurements radial velocities Segue 1 2 we derive a...
Observations of the gravitational radiation from well-localized, inspiraling compact-object binaries can measure absolute source distances with high accuracy. When coupled an independent determination redshift through electromagnetic counterpart, these standard sirens provide excellent probe expansion history Universe and dark energy. Short $\ensuremath{\gamma}$-ray bursts, if produced by merging neutron star binaries, would be known redshifts detectable ground-based wave (GW) networks such...
We investigate the origin of halo assembly bias, dependence clustering on history. relate to peak properties measured in Lagrangian space initial linear Gaussian random density field, and show how these same determine large-scale bias. focus two regimes where bias has been observed be significant: at masses very large small compared nonlinear mass scale. At high masses, we that is expected from statistics peaks fluctuations, extent found N-body simulations rare halos excellent agreement with...
The flux anomalies in four-image gravitational lenses can be interpreted as evidence for the dark matter substructure predicted by cold (CDM) halo models. In principle, these could arise from alternate sources, such absorption, scattering, or scintillation interstellar medium (ISM) of lens galaxy, problems ellipsoidal macro models used to fit systems, stellar microlensing. We apply several tests data that appear rule out explanations. First, radio show no significant dependence on...
We present a detailed investigation into which properties of CDM halos make them effective strong gravitational lenses. Strong-lensing cross sections 878 clusters from an N-body simulation are measured by ray-tracing through 13,594 unique projections. measure concentrations, axis ratios, orientations, and the substructure each cluster, compare lensing-weighted distribution quantity to that cluster population as whole. The concentrations lensing on average 34% larger than typical in universe....
ABSTRACT We show that the projected number density profiles of Sloan Digital Sky Survey photometric galaxies around galaxy clusters display strong evidence for splashback radius, a sharp halo edge corresponding to location first orbital apocenter satellite after their infall. split into two subsamples with different mean radial distances members, <?CDATA $\langle {R}_{{\rm{mem}}}\rangle $?> , at fixed richness and redshift. The sample smaller has ratio radius traditional boundary...
The friends-of-friends algorithm (hereafter, FOF) is a percolation which routinely used to identify dark matter halos from N-body simulations. We use results theory show that the boundary of FOF does not correspond single density threshold but range densities close critical value depends upon linking length parameter, b. for commonly choice b = 0.2, this equal 81.62 times mean density. Consequently, identified by enclose an average overdensity on their profile (concentration) and therefore...
We present a new method for simulating cosmologies that contain massive particles with thermal free streaming motion, such as neutrinos or warm/hot dark matter. This combines particle and fluid descriptions of the species to eliminate shot noise known plague conventional N-body simulations. describe this in detail, along results number test cases validate our method, check its range applicability. Using we demonstrate can produce significant scale-dependence large-scale biasing deep voids...
The fact that the clustering of dark matter halos depends not only on their mass, but also formation epoch, is a prominent, albeit subtle, feature cold structure theory, and known as assembly bias. At low mass scales ($\sim 10^{12}\,h^{-1}M_\odot$), early-forming are predicted to be more strongly clustered than late-forming ones. In this study we aim robustly detect signature bias observationally, making use time indicators central galaxies in proxy for halo history. Weak gravitational...
Recent work has shown that density profiles in the outskirts of dark matter halos can become extremely steep over a narrow range radius. This behavior is produced by splashback material on its first apocentric passage after accretion. We show location this feature may be understood quite simply, from principles. present simple model, based spherical collapse, accurately predicts without any free parameters. The important quantities determine radius are accretion rate and redshift.
Mass around dark matter halos can be divided into "infalling" material and "collapsed" that has passed through at least one pericenter. Analytical models simulations predict a rapid drop in the halo density profile associated with transition between these two regimes. Using data from SDSS, we explore evidence for such feature profiles of galaxy clusters investigate connection this possible phase space boundary. We first estimate steepening outer clusters: show an abrupt steepening, providing...
Cosmological neutrinos have their greatest influence in voids: these are the regions with highest neutrino to dark matter density ratios. The marked power spectrum can be used emphasize low over high regions, and therefore is potentially much more sensitive than effects of masses. Using 22,000 N-body simulations from Quijote suite, we quantify information content field, show that it outperforms standard by setting constraints improved a factor larger 2 on all cosmological parameters....
We report on a search for long duration microlensing events towards the Large Magellanic Cloud. find none, and therefore put limits contribution of high mass objects to Galactic dark matter. At 95% confidence level we exclude in range 0.3 solar masses 30.0 from contributing more than 4 times 10^11 halo. Combined with earlier results, this means that under 30 cannot make up entire matter halo if is typical size. For halo, 10 contribute less 40%
Dark energy models which alter the relative scaling behavior of dark and matter could provide a natural solution to cosmic coincidence problem-why densities are comparable today. A generalized class is introduced allows noncanonical ratio with Robertson-Walker scale factor a(t). We show that determining whether there problem, extent coincidence, can be addressed by several forthcoming experiments.
We present a detailed study of the viewing angles and geometry inner LMC (ρ ≲ 4°) based on sample more than 2000 MACHO Cepheids with complete {VR}KC light curves single-phase Two Micron All Sky Survey (2MASS) JHKs observations. The is considerably larger any previously studied subset has an improved areal coverage. Single-epoch random-phase 2MASS photometry corrected using V to derive mean magnitudes. analyze resulting period-luminosity relations in VRJHKs recover statistical reddening...
A new and powerful probe of the origin evolution structures in Universe has emerged been actively developed over last decade. In coming decade, non-Gaussianity, i.e., study non-Gaussian contributions to correlations cosmological fluctuations, will become an important both early late Universe. Specifically, it play a leading role furthering our understanding two fundamental aspects cosmology astrophysics: (i) physics very universe that created primordial seeds for large-scale structures, (ii)...
We report on the first results of an imaging survey to detect strong gravitational lensing targeting richest clusters selected from photometric data Sloan Digital Sky Survey (SDSS) with follow-up deep observations Wisconsin Indiana Yale NOAO (WIYN) 3.5m telescope and University Hawaii 88-inch (UH88). The are area 8000 deg^2 using Red Cluster Sequence technique span redshift range 0.1 < z 0.6, corresponding a comoving cosmological volume ~ 2 Gpc^3. Our thus targets more than order...
Motivated by the properties of early universe scenarios that produce observationally large local non-Gaussianity, we perform N-body simulations with non-Gaussian initial conditions from a generalized ansatz. The bispectra are schematically shape, but scale-dependent amplitude. We find in such cases size correction to bias small and mass objects depends on amplitude non-Gaussianity roughly scale object. In addition, some forms bispectrum alter dependence term fractional power k. These...
We derive radial mass profiles of four strong lensing selected clusters which show prominent giant arcs (Abell 1703, SDSS J1446+3032, J1531+3414, and J2111-0115), by combining detailed lens modeling with weak shear measured from deep Subaru Suprime-cam images. Weak signals are detected at high significance for all clusters, whose redshifts range z=0.28 to 0.64. demonstrate that adding information known arc significantly improves constraints on the density profile, compared those obtained...