743 research outputs found
Wide field weak lensing observations of A1835 and A2204
We present mass reconstructions from weak lensing for the galaxy clusters
A1835 and A2204 over 34'x34' fields using data from the ESO/MPG Wide Field
Imager. Using a background galaxy population of 22<R<25.5 we detect the
gravitational shear of A1835 at 8.8 sigma significance, and obtain best-fit
mass profiles of sigma_v=1233^{+66}_{-70} km/s for a singular isothermal sphere
model and r_{200}=1550 h^{-1} kpc, c=2.96 for a `universal' CDM profile. Using
a color-selected background galaxy population of 22<R<25.8 we detect the
gravitational shear of A2204 at 7.2 sigma significance, and obtain best-fit
mass profiles of sigma_v=1035^{+65}_{-71} km/s for a SIS model and r_{200}=1310
h^{-1} km/s, c=6.3 for a `universal' CDM profile. The gravitational shear at
distances greater than 10' is significantly detected for both clusters. The
best fit weak lensing cluster masses agree well with both X-ray and dynamical
mass measurements, although the central concentration of A1835 is much lower in
the weak lensing mass profile than that measured by recent Chandra results. We
suggest that this lower concentration is most likely a combination of
contamination of the 'background' galaxy population with cluster dwarf galaxies
and the effect of a prolate or tri-axial cluster core with the major axis lying
near the plane of the sky. We also detect a number of additional structures at
moderate significance, some of which appear to be sub-haloes associated with
the clusters.Comment: accepted to A&A, 14 pages, 13 figures, version with higher quality
images can be found at http://www.uni-bonn.de/~clow
Resource Letter: Gravitational Lensing
This Resource Letter provides a guide to a selection of the literature on
gravitational lensing and its applications. Journal articles, books, popular
articles, and websites are cited for the following topics: foundations of
gravitational lensing, foundations of cosmology, history of gravitational
lensing, strong lensing, weak lensing, and microlensing.Comment: Resource Letter, 2012, in press
(http://ajp.dickinson.edu/Readers/resLetters.html); 21 pages, no figures;
diigo version available at
http://groups.diigo.com/group/gravitational-lensin
Weak lensing mass reconstructions of the ESO Distant Cluster Survey
We present weak lensing mass reconstructions for the 20 high-redshift
clusters i n the ESO Distant Cluster Survey. The weak lensing analysis was
performed on deep, 3-color optical images taken with VLT/FORS2, using a
composite galaxy catalog with separate shape estimators measured in each
passband. We find that the EDisCS sample is composed primarily of clusters that
are less massive than t hose in current X-ray selected samples at similar
redshifts, but that all of the fields are likely to contain massive clusters
rather than superpositions of low mass groups. We find that 7 of the 20 fields
have additional massive structures which are not associated with the clusters
and which can affect the weak lensing mass determination. We compare the mass
measurements of the remaining 13 clusters with luminosity measurements from
cluster galaxies selected using photometric redshifts and find evidence of a
dependence of the cluster mass-to-light ratio with redshift. Finally we
determine the noise level in the shear measurements for the fields as a
function of exposure time and seeing and demonstrate that future ground-based
surveys which plan to perform deep optical imaging for use in weak lensing
measurements must achieve point-spread functions smaller than a median of 0.6"
FWHM.Comment: 35 pages, 24 figures, accepted to A&A, a version with better figure
resolution can be found at http://www.mpa-garching.mpg.de/ediscs/papers.htm
The origin of peak-offsets in weak-lensing maps
Centroid positions of peaks identified in weak lensing mass maps often show
offsets with respect to other means of identifying halo centres, like position
of the brightest cluster galaxy or X-ray emission centroid. Here we study the
effect of projected large-scale structure (LSS), smoothing of mass maps, and
shape noise on the weak lensing peak positions. Additionally we compare the
offsets in mass maps to those found in parametric model fits. Using ray-tracing
simulations through the Millennium Run -body simulation, we find that
projected LSS does not alter the weak-lensing peak position within the limits
of our simulations' spatial resolution, which exceeds the typical resolution of
weak lensing maps. We conclude that projected LSS, although a major contaminant
for weak-lensing mass estimates, is not a source of confusion for identifying
halo centres. The typically reported offsets in the literature are caused by a
combination of shape noise and smoothing alone. This is true for centroid
positions derived both from mass maps and model fits.Comment: 6 pages, 4 figures, accepted for publication in MNRAS, significant
additions to v
Weak Lensing by High-Redshift Clusters of Galaxies II: Mean Redshift of the Faint Background Galaxy Population
We use weak lensing shear measurements of six z>0.5 clusters of galaxies to
derive the mean lensing redshift of the background galaxies used to measure the
shear. Five of these clusters are compared to X-ray mass models and verify a
mean lensing redshift for a 23<R<26.3, R-I<0.9 background galaxy population in
good agreement with photometric redshift surveys of the HDF-S. The lensing
strength of the six clusters is also analyzed as a function of the magnitude of
the background galaxies, and an increase in shear with increasing magnitude is
detected at moderate significance. The change in the strength of the shear is
presumed to be caused by an increase in the mean redshift of the background
galaxies with increasing magnitude, and the degree of change detected is also
in agreement with those in photometric redshift surveys of the HDF-S.Comment: 6 pages, 4 figures, accepted by A&
Effects of asphericity and substructure on the determination of cluster mass with weak gravitational lensing
Weak gravitational lensing can be used to directly measure the mass along a
line-of-sight without any dependence on the dynamical state of the mass, and
thus can be used to measure the masses of clusters even if they are not
relaxed. One common technique used to measure cluster masses is fitting
azimuthally-averaged gravitational shear profiles with a spherical mass model.
In this paper we quantify how asphericity and projected substructure in
clusters can affect the virial mass and concentration measured with this
technique by simulating weak lensing observations on 30 independent
lines-of-sights through each of four high-resolution N-body cluster
simulations. We find that the variations in the measured virial mass and
concentration are of a size similar to the error expected in ideal weak lensing
observations and are correlated, but that the virial mass and concentration of
the mean shear profile agree well with that measured in three dimensional
models of the clusters. The dominant effect causing the variations is the
proximity of the line-of-sight to the major axis of the 3-D cluster mass
distribution, with projected substructure only causing minor perturbations in
the measured concentration. Finally we find that the best-fit "universal" CDM
models used to fit the shear profiles over-predict the surface density of the
clusters due to the cluster mass density falling off faster than the r^{-3}
model assumption.Comment: 10 pages, 10 figures, accepted by MNRA
Weak lensing observations of the "dark" cluster MG2016+112
We investigate the possible existence of a high-redshift (z=1) cluster of
galaxies associated with the QSO lens system MG2016+112. From an ultra-deep R-
and less deep V- and I-band Keck images and a K-band mosaic from UKIRT, we
detect ten galaxies with colors consistent with the lensing galaxy within
225h^{-1} kpc of the z=1.01 lensing galaxy. This represents an overdensity of
more than ten times the number density of galaxies with similar colors in the
rest of the image. We also find a group of seven much fainter objects closely
packed in a group only 27h^{-1} kpc north-west of the lensing galaxy. We
perform a weak lensing analysis on faint galaxies in the R-band image and
detect a mass peak of a size similar to the mass inferred from X-ray
observations of the field, but located 64" northwest of the lensing galaxy.
From the weak lensing data we rule out a similar sized mass peak centered on
the lensing galaxy at the 2 sigma level.Comment: 9 pages, 10 figures, submitted to A&A version with figure 4 at higher
resolution can be downloaded from
http://www.mpa-garching.mpg.de/~clowe/mg2016aa.ps.g
A New Look at Massive Clusters: weak lensing constraints on the triaxial dark matter halos of Abell 1689, Abell 1835, & Abell 2204
Measuring the 3D distribution of mass on galaxy cluster scales is a crucial
test of the LCDM model, providing constraints on the nature of dark matter.
Recent work investigating mass distributions of individual galaxy clusters
(e.g. Abell 1689) using weak and strong gravitational lensing has revealed
potential inconsistencies between the predictions of structure formation models
relating halo mass to concentration and those relationships as measured in
massive clusters. However, such analyses employ simple spherical halo models
while a growing body of work indicates that triaxial 3D halo structure is both
common and important in parameter estimates. We recently introduced a Markov
Chain Monte Carlo (MCMC) method to fit fully triaxial models to weak lensing
data that gives parameter and error estimates that fully incorporate the true
shape uncertainty present in nature. In this paper we apply that method to weak
lensing data obtained with the ESO/MPG Wide-Field Imager for galaxy clusters
A1689, A1835, and A2204, under a range of Bayesian priors derived from theory
and from independent X-ray and strong lensing observations. For Abell 1689,
using a simple strong lensing prior we find marginalized mean parameter values
M_200 = (0.83 +- 0.16)x10^15 M_solar/h and C=12.2 +- 6.7, which are marginally
consistent with the mass-concentration relation predicted in LCDM. The large
error contours that accompany our triaxial parameter estimates more accurately
represent the true extent of our limited knowledge of the structure of galaxy
cluster lenses, and make clear the importance of combining many constraints
from other theoretical, lensing (strong, flexion), or other observational
(X-ray, SZ, dynamical) data to confidently measure cluster mass profiles.
(Abridged)Comment: 21 pages, 10 figures, accepted for publication in MNRA
Weak lensing evidence for a filament between A222/A223
We present a weak lensing analysis and comparison to optical and X-ray maps
of the close pair of massive clusters A222/223. Indications for a filamentary
connection between the clusters are found and discussed.Comment: 6 pages, 1 figure. To appear in Proc. IAU Colloquium 195: Outskirts
of Galaxy Clusters - Intense Life in the Suburbs. Version with higher
resolution available at
http://www.astro.uni-bonn.de/~dietrich/torino_proc.ps.g
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