2,077 research outputs found
Cosmological Constraints from the SDSS maxBCG Cluster Catalog
We use the abundance and weak lensing mass measurements of the SDSS maxBCG
cluster catalog to simultaneously constrain cosmology and the richness--mass
relation of the clusters. Assuming a flat \LambdaCDM cosmology, we find
\sigma_8(\Omega_m/0.25)^{0.41} = 0.832\pm 0.033 after marginalization over all
systematics. In common with previous studies, our error budget is dominated by
systematic uncertainties, the primary two being the absolute mass scale of the
weak lensing masses of the maxBCG clusters, and uncertainty in the scatter of
the richness--mass relation. Our constraints are fully consistent with the WMAP
five-year data, and in a joint analysis we find \sigma_8=0.807\pm 0.020 and
\Omega_m=0.265\pm 0.016, an improvement of nearly a factor of two relative to
WMAP5 alone. Our results are also in excellent agreement with and comparable in
precision to the latest cosmological constraints from X-ray cluster abundances.
The remarkable consistency among these results demonstrates that cluster
abundance constraints are not only tight but also robust, and highlight the
power of optically-selected cluster samples to produce precision constraints on
cosmological parameters.Comment: comments welcom
The clustering of massive galaxies at z~0.5 from the first semester of BOSS data
We calculate the real- and redshift-space clustering of massive galaxies at
z~0.5 using the first semester of data by the Baryon Oscillation Spectroscopic
Survey (BOSS). We study the correlation functions of a sample of 44,000 massive
galaxies in the redshift range 0.4<z<0.7. We present a halo-occupation
distribution modeling of the clustering results and discuss the implications
for the manner in which massive galaxies at z~0.5 occupy dark matter halos. The
majority of our galaxies are central galaxies living in halos of mass
10^{13}Msun/h, but 10% are satellites living in halos 10 times more massive.
These results are broadly in agreement with earlier investigations of massive
galaxies at z~0.5. The inferred large-scale bias (b~2) and relatively high
number density (nbar=3e-4 h^3 Mpc^{-3}) imply that BOSS galaxies are excellent
tracers of large-scale structure, suggesting BOSS will enable a wide range of
investigations on the distance scale, the growth of large-scale structure,
massive galaxy evolution and other topics.Comment: 11 pages, 12 figures, matches version accepted by Ap
Redshift evolution of the 1.4 GHz volume averaged radio luminosity function in clusters of galaxies
By cross-correlating large samples of galaxy clusters with publicly available
radio source catalogs, we construct the volume-averaged radio luminosity
function (RLF) in clusters of galaxies, and investigate its dependence on
cluster redshift and mass. In addition, we determine the correlation between
the cluster mass and the radio luminosity of the brightest source within 50 kpc
from the cluster center. We use two cluster samples: the optically selected
maxBCG cluster catalog and a composite sample of X-ray selected clusters. The
radio data come from the VLA NVSS and FIRST surveys. We use scaling relations
to estimate cluster masses and radii to get robust estimates of cluster
volumes. We determine the projected radial distribution of sources, for which
we find no dependence on luminosity or cluster mass. Background and foreground
sources are statistically accounted for, and we account for confusion of radio
sources by adaptively degrading the resolution of the radio source surveys. We
determine the redshift evolution of the RLF under the assumption that its
overall shape does not change with redshift. Our results are consistent with a
pure luminosity evolution of the RLF in the range 0.1 < z < 0.3 from the
optical cluster sample. The X-ray sample extends to higher redshift and yields
results also consistent with a pure luminosity evolution. We find no direct
evidence of a dependence of the RLF on cluster mass from the present data,
although the data are consistent with the most luminous sources only being
found in high-mass systems.Comment: Accepted for publication in A&
A theoretical framework for combining techniques that probe the link between galaxies and dark matter
We develop a theoretical framework that combines measurements of
galaxy-galaxy lensing, galaxy clustering, and the galaxy stellar mass function
in a self-consistent manner. While considerable effort has been invested in
exploring each of these probes individually, attempts to combine them are still
in their infancy despite the potential of such combinations to elucidate the
galaxy-dark matter connection, to constrain cosmological parameters, and to
test the nature of gravity. In this paper, we focus on a theoretical model that
describes the galaxy-dark matter connection based on standard halo occupation
distribution techniques. Several key modifications enable us to extract
additional parameters that determine the stellar-to-halo mass relation and to
simultaneously fit data from multiple probes while allowing for independent
binning schemes for each probe. In a companion paper, we demonstrate that the
model presented here provides an excellent fit to galaxy-galaxy lensing, galaxy
clustering, and stellar mass functions measured in the COSMOS survey from z=0.2
to z=1.0. We construct mock catalogs from numerical simulations to investigate
the effects of sample variance and covariance on each of the three probes.
Finally, we analyze and discuss how trends in each of the three observables
impact the derived parameters of the model. In particular, we investigate the
various features of the observed galaxy stellar mass function (low-mass slope,
plateau, knee, and high-mass cut-off) and show how each feature is related to
the underlying relationship between stellar and halo mass. We demonstrate that
the observed plateau feature in the stellar mass function at Mstellar~2x10^10
Msun is due to the transition that occurs in the stellar-to-halo mass relation
at Mhalo ~ 10^12 Msun from a low-mass power-law regime to a sub-exponential
function at higher stellar mass.Comment: 21 pages. Accepted to Ap
Galaxy-galaxy Lensing: Dissipationless Simulations Versus the Halo Model
Galaxy-galaxy lensing is a powerful probe of the relation between galaxies
and dark matter halos, but its theoretical interpretation requires a careful
modeling of various contributions, such as the contribution from central and
satellite galaxies. For this purpose, a phenomenological approach based on the
halo model has been developed, allowing for fast exploration of the parameter
space of models. In this paper, we investigate the ability of the halo model to
extract information from the g-g weak lensing signal by comparing it to
high-resolution dissipationless simulations that resolve subhalos. We find that
the halo model reliably determines parameters such as the host halo mass of
central galaxies, the fraction of galaxies that are satellites, and their
radial distribution inside larger halos. If there is a significant scatter
present in the central galaxy host halo mass distribution, then the mean and
median mass of that distribution can differ significantly from one another, and
the halo model mass determination lies between the two. This result suggests
that when analyzing the data, galaxy subsamples with a narrow central galaxy
halo mass distribution, such as those based on stellar mass, should be chosen
for a simpler interpretation of the results.Comment: 13 pages, 6 figures; minor changes made, matches MNRAS accepted
versio
The clustering of intermediate redshift quasars as measured by the Baryon Oscillation Spectroscopic Survey
We measure the quasar two-point correlation function over the redshift range
2.2<z<2.8 using data from the Baryon Oscillation Spectroscopic Survey. We use a
homogeneous subset of the data consisting of 27,129 quasars with spectroscopic
redshifts---by far the largest such sample used for clustering measurements at
these redshifts to date. The sample covers 3,600 square degrees, corresponding
to a comoving volume of 9.7(Gpc/h)^3 assuming a fiducial LambdaCDM cosmology,
and it has a median absolute i-band magnitude of -26, k-corrected to z=2. After
accounting for redshift errors we find that the redshift space correlation
function is fit well by a power-law of slope -2 and amplitude s_0=(9.7\pm
0.5)Mpc/h over the range 3<s<25Mpc/h. The projected correlation function, which
integrates out the effects of peculiar velocities and redshift errors, is fit
well by a power-law of slope -1 and r_0=(8.4\pm 0.6)Mpc/h over the range
4<R<16Mpc/h. There is no evidence for strong luminosity or redshift dependence
to the clustering amplitude, in part because of the limited dynamic range in
our sample. Our results are consistent with, but more precise than, previous
measurements at similar redshifts. Our measurement of the quasar clustering
amplitude implies a bias factor of b~3.5 for our quasar sample. We compare the
data to models to constrain the manner in which quasars occupy dark matter
halos at z~2.4 and infer that such quasars inhabit halos with a characteristic
mass of ~10^{12}Msun/h with a duty cycle for the quasar activity of 1 per
cent.Comment: 20 pages, 18 figures. Minor modifications to match version accepted
by journa
Halo Occupation Distribution Modeling of Clustering of Luminous Red Galaxies
We perform Halo Occupation Distribution (HOD) modeling to interpret
small-scale and intermediate-scale clustering of 35,000 luminous early-type
galaxies and their cross-correlation with a reference imaging sample of normal
L* galaxies in the Sloan Digital Sky Survey. The modeling results show that
most of these luminous red galaxies (LRGs) are central galaxies residing in
massive halos of typical mass M ~ a few times 10^13 to 10^14 Msun/h, while a
few percent of them have to be satellites within halos in order to produce the
strong auto-correlations exhibited on smaller scales. The mean luminosity Lc of
central LRGs increases with the host halo mass, with a rough scaling relation
of Lc \propto M^0.5. The halo mass required to host on average one satellite
LRG above a luminosity threshold is found to be about 10 times higher than that
required to host a central LRG above the same threshold. We find that in
massive halos the distribution of L* galaxies roughly follows that of the dark
matter and their mean occupation number scales with halo mass as M^1.5. The HOD
modeling results also allows for an intuitive understanding of the
scale-dependent luminosity dependence of the cross-correlation between LRGs and
L_* galaxies. Constraints on the LRG HOD provide tests to models of formation
and evolution of massive galaxies, and they are also useful for cosmological
parameter investigations. In one of the appendices, we provide LRG HOD
parameters with dependence on cosmology inferred from modeling the two-point
auto-correlation functions of LRGs.Comment: 21 pages, 10 figures, accepted for publication in Ap
Weak lensing, dark matter and dark energy
Weak gravitational lensing is rapidly becoming one of the principal probes of
dark matter and dark energy in the universe. In this brief review we outline
how weak lensing helps determine the structure of dark matter halos, measure
the expansion rate of the universe, and distinguish between modified gravity
and dark energy explanations for the acceleration of the universe. We also
discuss requirements on the control of systematic errors so that the
systematics do not appreciably degrade the power of weak lensing as a
cosmological probe.Comment: Invited review article for the GRG special issue on gravitational
lensing (P. Jetzer, Y. Mellier and V. Perlick Eds.). V3: subsection on
three-point function and some references added. Matches the published versio
The Sloan Digital Sky Survey Quasar Lens Search. II. Statistical lens sample from the third data release
We report the first results of our systematic search for strongly lensed quasars using the spectroscopically confirmed quasars in the Sloan Digital Sky Survey (SDSS). Among 46,420 quasars from the SDSS Data Release 3 (~4188 deg^2), we select a subsample of 22,683 quasars that are located at redshifts between 0.6 and 2.2 and are brighter than the Galactic extinction-corrected i-band magnitude of 19.1. We identify 220 lens candidates from the quasar subsample, for which we conduct extensive and systematic follow-up observations in optical and near-infrared wavebands, in order to construct a complete lensed quasar sample at image separations between 1" and 20" and flux ratios of faint to bright lensed images larger than 10^(−0.5). We construct a statistical sample of 11 lensed quasars. Ten of these are galaxy-scale lenses with small image separations (~ 1"-2") and one is a large separation (15") system which is produced by a massive cluster of galaxies, representing the first statistical sample of lensed quasars including both galaxy- and cluster-scale lenses. The Data Release 3 spectroscopic quasars contain an additional 11 lensed quasars outside the statistical sample
The SDSS-III Baryon Oscillation Spectroscopic Survey: Quasar Target Selection for Data Release Nine
The SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS), a five-year
spectroscopic survey of 10,000 deg^2, achieved first light in late 2009. One of
the key goals of BOSS is to measure the signature of baryon acoustic
oscillations in the distribution of Ly-alpha absorption from the spectra of a
sample of ~150,000 z>2.2 quasars. Along with measuring the angular diameter
distance at z\approx2.5, BOSS will provide the first direct measurement of the
expansion rate of the Universe at z > 2. One of the biggest challenges in
achieving this goal is an efficient target selection algorithm for quasars over
2.2 < z < 3.5, where their colors overlap those of stars. During the first year
of the BOSS survey, quasar target selection methods were developed and tested
to meet the requirement of delivering at least 15 quasars deg^-2 in this
redshift range, out of 40 targets deg^-2. To achieve these surface densities,
the magnitude limit of the quasar targets was set at g <= 22.0 or r<=21.85.
While detection of the BAO signature in the Ly-alpha absorption in quasar
spectra does not require a uniform target selection, many other astrophysical
studies do. We therefore defined a uniformly-selected subsample of 20 targets
deg^-2, for which the selection efficiency is just over 50%. This "CORE"
subsample will be fixed for Years Two through Five of the survey. In this paper
we describe the evolution and implementation of the BOSS quasar target
selection algorithms during the first two years of BOSS operations. We analyze
the spectra obtained during the first year. 11,263 new z>2.2 quasars were
spectroscopically confirmed by BOSS. Our current algorithms select an average
of 15 z > 2.2 quasars deg^-2 from 40 targets deg^-2 using single-epoch SDSS
imaging. Multi-epoch optical data and data at other wavelengths can further
improve the efficiency and completeness of BOSS quasar target selection.
[Abridged]Comment: 33 pages, 26 figures, 12 tables and a whole bunch of quasars.
Submitted to Ap
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