425 research outputs found
Completeness in Photometric and Spectroscopic Searches for Clusters
We investigate, using simulated galaxy catalogues, the completeness of
searches for massive clusters of galaxies in redshift surveys or imaging
surveys with photometric redshift estimates, i.e. what fraction of clusters
(M>10^14/h Msun) are found in such surveys. We demonstrate that the matched
filter method provides an efficient and reliable means of identifying massive
clusters even when the redshift estimates are crude. In true redshift surveys
the method works extremely well. We demonstrate that it is possible to
construct catalogues with high completeness, low contamination and both varying
little with redshift.Comment: ApJ in press, 15 pages, 10 figure
The Effect of the Cosmic Web on Cluster Weak Lensing Mass Estimates
In modern hierarchical theories of structure formation, rich clusters of
galaxies form at the vertices of a weblike distribution of matter, with
filaments emanating from them to large distances and with smaller objects
forming and draining in along these filaments. The amount of mass contained in
structure near the cluster can be comparable to the collapsed mass of the
cluster itself. As the lensing kernel is quite broad along the line of sight
around cluster lenses with typical redshifts near z=0.5, structures many Mpc
away from the cluster are essentially at the same location as the cluster
itself, when considering their effect on the cluster's weak lensing signal. We
use large-scale numerical simulations of structure formation in a
Lambda-dominated cold dark matter model to quantify the effect that large-scale
structure near clusters has upon the cluster masses deduced from weak lensing
analysis. A correction for the scatter in possible observed lensing masses
should be included when interpreting mass functions from weak lensing surveys.Comment: 14 pages, 11 figures. LaTeX2e, uses emulateapj.sty and
onecolfloat.st
A Redshift Survey of Nearby Galaxy Groups: the Shape of the Mass Density Profile
We constrain the mass profile and orbital structure of nearby groups and
clusters of galaxies. Our method yields the joint probability distribution of
the density slope n, the velocity anisotropy beta, and the turnover radius r0
for these systems. The measurement technique does not use results from N-body
simulations as priors. We incorporate 2419 new redshifts in the fields of 41
systems of galaxies with z < 0.04. The new groups have median velocity
dispersion sigma=360 km/s. We also use 851 archived redshifts in the fields of
8 nearly relaxed clusters with z < 0.1. Within R < 2 r200, the data are
consistent with a single power law matter density distribution with slope n =
1.8-2.2 for systems with sigma < 470 km/s, and n = 1.6-2.0 for those with sigma
> 470 km/s (95% confidence). We show that a simple, scale-free phase space
distribution function f(E,L^2) ~ (-E)^(alpha-1/2) L^(-2 \beta) is consistent
with the data as long as the matter density has a cusp. Using this DF, matter
density profiles with constant density cores (n=0) are ruled out with better
than 99.7% confidence.Comment: 22 pages; accepted for publication in the Astrophysical Journa
ROSAT PSPC Observations of the Richest () ACO Clusters
We have compiled an X-ray catalog of optically selected rich clusters of
galaxies observed by the PSPC during the pointed GO phase of the ROSAT mission.
This paper contains a systematic X-ray analysis of 150 clusters with an optical
richness classification of from the ACO catalog (Abell, Corwin, and
Olowin 1989). All clusters were observed within 45' of the optical axis of the
telescope during pointed PSPC observations. For each cluster, we calculate: the
net 0.5-2.0 keV PSPC count rate (or upper limit) in a 1 Mpc radius
aperture, 0.5-2.0 keV flux and luminosity, bolometric luminosity, and X-ray
centroid. The cluster sample is then used to examine correlations between the
X-ray and optical properties of clusters, derive the X-ray luminosity function
of clusters with different optical classifications, and obtain a quantitative
estimate of contamination (i.e, the fraction of clusters with an optical
richness significantly overestimated due to interloping galaxies) in the ACO
catalog
Mass Models and Sunyaev-Zeldovich Effect Predictions for a Flux Limited Sample of 22 Nearby X-Ray Clusters
We define a 90% complete, volume-limited sample of 31 z<0.1 x-ray clusters
and present a systematic analysis of public ROSAT PSPC data on 22 of these
objects. Our efforts are undertaken in support of the Penn/OVRO SZE survey, and
to this end we present predictions for the inverse Compton optical depth
towards all 22 of these clusters. We have performed detailed Monte Carlo
simulations to understand the effects of the cluster profile uncertainties on
the SZE predictions given the OVRO 5.5-meter telescope beam and switching
patterns; we find that the profile uncertainties are one of the least
significant components of our error budget for SZE-based distance measurements.
We also present baryonic masses and baryon mass fractions derived under the
assumption of hydrostatic equilibrium for these 22 clusters. The mean baryonic
mass fraction within R_500 \sim 500 h^-1 kpc is (7.02 \pm 0.28) x 10^-2 h^-3/2,
or (19.8 \pm 0.8) x 10^-2 for h=0.5. We confirm the Allen et al. (1993) claim
of an excess absorbing column density towards Abell 478, but do not find
similar anomalies in the other 21 clusters in our sample. We also find some
evidence for an excess of soft counts in the ROSAT PSPC data.
A measurement of H_o using these models and OVRO SZE determinations will be
presented in a second paper.Comment: 51 pages, 6 figures included in text. Added comparison of different
cosmologies; accepted for publication in Ap
The Las Campanas Distant Cluster Survey -- The Correlation Function
We present the first non-local (z>0.2) measurement of the cluster-cluster
spatial correlation length, using data from the Las Campanas Distant Cluster
Survey (LCDCS). We measure the angular correlation function for
velocity-dispersion limited subsamples of the catalog at estimated redshifts of
0.35<z_{est}<0.575, and derive spatial correlation lengths for these clusters
via the cosmological Limber equation. The correlation lengths that we measure
for clusters in the LCDCS are consistent both with local results for the APM
cluster catalog and with theoretical expectations based upon the Virgo
Consortium Hubble Volume simulations and the analytic predictions. Despite
samples containing over 100 clusters, our ability to discriminate between
cosmological models is limited because of statistical uncertainty.Comment: 7 pages, 4 figures, accepted to ApJ (v571, May 20, 2002
Correlation length of X-ray brightest Abell clusters
We compute the cluster auto-correlation function of an X-ray
flux limited sample of Abell clusters (XBACs, \cite{ebe}). For the total XBACs
sample we find a power-law fit with Mpc
hand consistent with the results of Abell
clusters. We also analyze for subsamples defined by different
X-ray luminosity thresholds where we find a weak tendency of larger values of
with increasing X-ray luminosity although with a low statistical
significance. In the different subsamples analyzed we find Mpc
h and . Our analysis suggests that cluster X-ray
luminosities may be used for a reliable confrontation of cluster spatial
distribution properties in models and observations.Comment: Accepted for publication in Astrophysical Journa
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