3,023 research outputs found
Propagating Residual Biases in Cosmic Shear Power Spectra
In this paper we derive a full expression for the propagation of
multiplicative and additive shape measurement biases into the cosmic shear
power spectrum. In doing so we identify several new terms that are associated
with selection effects, as well as cross-correlation terms between the
multiplicative and additive biases and the shear field. The computation of the
resulting bias in the shear power spectrum scales as the fifth power of the
maximum multipole considered. Consequently the calculation is unfeasible for
large l-modes, and the only tractable way to assess the full impact of shape
measurement biases on cosmic shear power spectrum is through forward modelling
of the effects. To linear order in bias parameters the shear power spectrum is
only affected by the mean of the multiplicative bias field over a survey and
the cross correlation between the additive bias field and the shear field. If
the mean multiplicative bias is zero then second order convolutive terms are
expected to be orders of magnitude smaller.Comment: 10 pages, accepted to the Open Journal of Astrophysic
Matthew D. Holm, percussion
Martine Wesley-SmithJacob DruckmanChristopher DeaneBob Becke
First detection of galaxy-galaxy-galaxy lensing in RCS. A new tool for studying the matter environment of galaxy pairs
The weak gravitational lensing effect, small coherent distortions of galaxy
images by means of a gravitational tidal field, can be used to study the
relation between the matter and galaxy distribution. In this context, weak
lensing has so far only been used for considering a second-order correlation
function that relates the matter density and galaxy number density as a
function of separation. We implement two new, third-order correlation functions
that have recently been suggested in the literature, and apply them to the
Red-Sequence Cluster Survey. We demonstrate that it is possible, even with
already existing data, to make significant measurements of third-order lensing
correlations. We develop an optimised computer code for the correlation
functions. To test its reliability a set of tests are performed. The
correlation functions are transformed to aperture statistics, which allow easy
tests for remaining systematics in the data. In order to further verify the
robustness of our measurement, the signal is shown to vanish when randomising
the source ellipticities. Finally, the lensing signal is compared to crude
predictions based on the halo-model. On angular scales between roughly 1 arcmin
and 11 arcmin a significant third-order correlation between two lens positions
and one source ellipticity is found. We discuss this correlation function as a
novel tool to study the average matter environment of pairs of galaxies.
Correlating two source ellipticities and one lens position yields a less
significant but nevertheless detectable signal on a scale of 4 arcmin. Both
signals lie roughly within the range expected by theory which supports their
cosmological origin.[ABRIDGED]Comment: 15 pages, 12 figures, accepted by A&A; minor change
Multiwavelength Mass Comparisons of the z~0.3 CNOC Cluster Sample
Results are presented from a detailed analysis of optical and X-ray
observations of moderate-redshift galaxy clusters from the Canadian Network for
Observational Cosmology (CNOC) subsample of the EMSS. The combination of
extensive optical and deep X-ray observations of these clusters make them ideal
candidates for multiwavelength mass comparison studies. X-ray surface
brightness profiles of 14 clusters with 0.17<z<0.55 are constructed from
Chandra observations and fit to single and double beta-models. Spatially
resolved temperature analysis is performed, indicating that five of the
clusters in this sample exhibit temperature gradients within their inner 60-200
kpc. Integrated spectra extracted within R_2500 provide temperature, abundance,
and luminosity information. Under assumptions of hydrostatic equilibrium and
spherical symmetry, we derive gas and total masses within R_2500 and R_200. We
find an average gas mass fraction within R_200 of 0.136 +/- 0.004, resulting in
Omega_m=0.28 +/- 0.01 (formal error). We also derive dynamical masses for these
clusters to R_200. We find no systematic bias between X-ray and dynamical
methods across the sample, with an average M(dyn)/M(X-ray) = 0.97 +/- 0.05. We
also compare X-ray masses to weak lensing mass estimates of a subset of our
sample, resulting in a weighted average of M(lens)/M(X-ray) of 0.99 +/- 0.07.
We investigate X-ray scaling relationships and find powerlaw slopes which are
slightly steeper than the predictions of self-similar models, with an E(z)^(-1)
Lx-Tx slope of 2.4 +/- 0.2 and an E(z) M_2500-Tx slope of 1.7 +/- 0.1.
Relationships between red-sequence optical richness (B_gc,red) and global
cluster X-ray properties (Tx, Lx and M_2500) are also examined and fitted.Comment: Astrophysical Journal, 48 pages, 11 figures, LaTeX. Added correction
to surface brightness normalization of MS1512.4+3647, corrections to sample
gas mass fractions and calculated value of Omega_m. Figure resolution has
been reduced to comply with astro-ph upload requirement
Properties of galaxy dark matter halos from weak lensing
We present the results of a study of weak lensing by galaxies based on 45.5
deg of band imaging data from the Red-Sequence Cluster Survey (RCS).
We present the first weak lensing detection of the flattening of galaxy dark
matter halos. We use a simple model in which the ellipticity of the halo is
times the observed ellipticity of the lens. We find a best fit value of
, suggesting that the dark matter halos are somewhat
rounder than the light distribution. The fact that we detect a significant
flattening implies that the halos are well aligned with the light distribution.
Given the average ellipticity of the lenses, this implies a halo ellipticity of
, in fair agreement with results from
numerical simulations of CDM. This result provides strong support for the
existence of dark matter, as an isotropic lensing signal is excluded with 99.5%
confidence. We also study the average mass profile around the lenses, using a
maximum likelihood analysis. We consider two models for the halo mass profile:
a truncated isothermal sphere (TIS) and an NFW profile. We adopt
observationally motivated scaling relations between the lens luminosity and the
velocity dispersion and the extent of the halo. The best fit NFW model yields a
mass and a scale
radius kpc. This value for the scale radius is
in excellent agreement with predictions from numerical simulations for a halo
of this mass.Comment: Significantly revised version, accepted for publication in ApJ 11
pages, 6 figure
- …