45 research outputs found
Evolution of the luminosity-to-halo mass relation of LRGs from a combined SDSS-DR10+RCS2 analysis
We study the evolution of the luminosity-to-halo mass relation of Luminous
Red Galaxies (LRGs). We select a sample of 52 000 LOWZ and CMASS LRGs from the
Baryon Oscillation Spectroscopic Survey (BOSS) SDSS-DR10 in the ~450 deg^2 that
overlaps with imaging data from the second Red-sequence Cluster Survey (RCS2),
group them into bins of absolute magnitude and redshift and measure their weak
lensing signals. The source redshift distribution has a median of 0.7, which
allows us to study the lensing signal as a function of lens redshift. We
interpret the lensing signal using a halo model, from which we obtain the halo
masses as well as the normalisations of the mass-concentration relations. We
find that the concentration of haloes that host LRGs is consistent with dark
matter only simulations once we allow for miscentering or satellites in the
modelling. The slope of the luminosity-to-halo mass relation has a typical
value of 1.4 and does not change with redshift, but we do find evidence for a
change in amplitude: the average halo mass of LOWZ galaxies increases by
25_{-14}^{+16} % between z=0.36 and 0.22 to an average value of 6.43+/-0.52 x
10^13 h70^-1 Msun. If we extend the redshift range using the CMASS galaxies and
assume that they are the progenitors of the LOWZ sample, we find that the
average mass of LRGs increases by 80^{+39}_{-28} % between z=0.6 and 0.2Comment: 20 pages, 11 figures, accepted for publication in A&
Galaxy-Dark Matter Connection : from Astrophysics to Cosmology
Galaxy-galaxy (g-g) lensing represents an ideal technique to constrain the dark matter distribution on galaxy scales. The required accuracy in the signal can be achieved only by stacking many foreground galaxies and averaging the ellipticity of the resulting background galaxies. Unfortunately, the stacking procedure complicates any astrophysical interpretation. In order to extract information from the composite g-g lensing signal, a reliable model of the way galaxies populate dark matter haloes is required. We use a realistic description of the halo occupation statistics based on the conditional luminosity function. It provides a statistical prescription for the number of galaxies with a given luminosity living in dark matter haloes of a given mass. Being “a priori” constrained by the luminosity dependence of the galaxy clustering, it can be used for predicting the g-g lensing signal without any additional tuning. Our model allows a thorough understanding of the different terms contributing to the signal. We carefully explore the effect of the assumptions entering the model. Our theoretical predictions are in very good agreement with SDSS data. Furthermore, we use the sensitivity of this technique to the underlying cosmological model to study the feasibility of a joint analysis of galaxy clustering and g-g lensing as a novel technique to constrain the values of cosmological parameters such as Omega_m and sigma_8 . We show that uncertainties and systematics in the model do not significantly affect the model predictions. We conclude that a combined analysis of galaxy clustering and g-g lensing can be used as a novel, complementary and competitive technique to constrain cosmological parameters
The Canadian Cluster Comparison Project: detailed study of systematics and updated weak lensing masses
Masses of clusters of galaxies from weak gravitational lensing analyses of
ever larger samples are increasingly used as the reference to which baryonic
scaling relations are compared. In this paper we revisit the analysis of a
sample of 50 clusters studied as part of the Canadian Cluster Comparison
Project. We examine the key sources of systematic error in cluster masses. We
quantify the robustness of our shape measurements and calibrate our algorithm
empirically using extensive image simulations. The source redshift distribution
is revised using the latest state-of-the-art photometric redshift catalogs that
include new deep near-infrared observations. Nonetheless we find that the
uncertainty in the determination of photometric redshifts is the largest source
of systematic error for our mass estimates. We use our updated masses to
determine b, the bias in the hydrostatic mass, for the clusters detected by
Planck. Our results suggest 1-b=0.76+-0.05(stat)}+-0.06(syst)}, which does not
resolve the tension with the measurements from the primary cosmic microwave
background.Comment: resubmitted to MNRAS after review by refere
Galaxy alignments: An overview
The alignments between galaxies, their underlying matter structures, and the
cosmic web constitute vital ingredients for a comprehensive understanding of
gravity, the nature of matter, and structure formation in the Universe. We
provide an overview on the state of the art in the study of these alignment
processes and their observational signatures, aimed at a non-specialist
audience. The development of the field over the past one hundred years is
briefly reviewed. We also discuss the impact of galaxy alignments on
measurements of weak gravitational lensing, and discuss avenues for making
theoretical and observational progress over the coming decade.Comment: 43 pages excl. references, 16 figures; minor changes to match version
published in Space Science Reviews; part of a topical volume on galaxy
alignments, with companion papers at arXiv:1504.05546 and arXiv:1504.0546
Galaxy alignments: Observations and impact on cosmology
Galaxy shapes are not randomly oriented, rather they are statistically
aligned in a way that can depend on formation environment, history and galaxy
type. Studying the alignment of galaxies can therefore deliver important
information about the physics of galaxy formation and evolution as well as the
growth of structure in the Universe. In this review paper we summarise key
measurements of galaxy alignments, divided by galaxy type, scale and
environment. We also cover the statistics and formalism necessary to understand
the observations in the literature. With the emergence of weak gravitational
lensing as a precision probe of cosmology, galaxy alignments have taken on an
added importance because they can mimic cosmic shear, the effect of
gravitational lensing by large-scale structure on observed galaxy shapes. This
makes galaxy alignments, commonly referred to as intrinsic alignments, an
important systematic effect in weak lensing studies. We quantify the impact of
intrinsic alignments on cosmic shear surveys and finish by reviewing practical
mitigation techniques which attempt to remove contamination by intrinsic
alignments.Comment: 52 pages excl. references, 16 figures; minor changes to match version
published in Space Science Reviews; part of a topical volume on galaxy
alignments, with companion papers arXiv:1504.05456 and arXiv:1504.0554
Satellite Kinematics I: A New Method to Constrain the Halo Mass-Luminosity Relation of Central Galaxies
Satellite kinematics can be used to probe the masses of dark matter haloes of
central galaxies. In order to measure the kinematics with sufficient
signal-to-noise, one uses the satellite galaxies of a large number of central
galaxies stacked according to similar properties (e.g., luminosity). However,
in general the relation between the luminosity of a central galaxy and the mass
of its host halo will have non-zero scatter. Consequently, this stacking
results in combining the kinematics of satellite galaxies in haloes of
different masses, which complicates the interpretation of the data. In this
paper we present an analytical framework to model satellite kinematics,
properly accounting for this scatter and for various selection effects. We show
that in the presence of scatter in the halo mass-luminosity relation, the
commonly used velocity dispersion of satellite galaxies can not be used to
infer a unique halo mass-luminosity relation. In particular, we demonstrate
that there is a degeneracy between the mean and the scatter of the halo
mass-luminosity relation. We present a new technique that can break this
degeneracy, and which involves measuring the velocity dispersions using two
different weighting schemes: host-weighting (each central galaxy gets the same
weight) and satellite-weighting (each central galaxy gets a weight proportional
to its number of satellites). The ratio between the velocity dispersions
obtained using these two weighting schemes is a strong function of the scatter
in the halo mass-luminosity relation, and can thus be used to infer a unique
relation between light and mass from the kinematics of satellite galaxies.Comment: 8 pages, 3 figures, MNRAS submitte
Satellite Kinematics II: The Halo Mass-Luminosity Relation of Central Galaxies in SDSS
The kinematics of satellite galaxies reflect the masses of the extended dark
matter haloes in which they orbit, and thus shed light on the mass-luminosity
relation (MLR) of their corresponding central galaxies. In this paper we select
a large sample of centrals and satellites from the Sloan Digital Sky Survey
(SDSS) and measure the kinematics (velocity dispersions) of the satellite
galaxies as a function of the -band luminosity of the central galaxies.
Using the analytical framework presented in Paper I, we use these data to infer
{\it both} the mean and the scatter of the MLR of central galaxies, carefully
taking account of selection effects and biases introduced by the stacking
procedure. As expected, brighter centrals on average reside in more massive
haloes. In addition, we find that the scatter in halo masses for centrals of a
given luminosity, , also increases with increasing luminosity.
As we demonstrate, this is consistent with , which reflects
the scatter in the conditional probability function , being
independent of halo mass. Our analysis of the satellite kinematics yields
, in excellent agreement with constraints from
clustering and group catalogues, and with predictions from a semi-analytical
model of galaxy formation. We thus conclude that the amount of stochasticity in
galaxy formation, which is characterized by , is well
constrained, is independent of halo mass, and is in good agreement with current
models of galaxy formation.Comment: 17 pages, 12 figures, MNRAS submitte