378,682 research outputs found
The X-CLASS - redMaPPer galaxy cluster comparison: I. Identification procedures
We performed a detailed and, for a large part interactive, analysis of the
matching output between the X-CLASS and redMaPPer cluster catalogues. The
overlap between the two catalogues has been accurately determined and possible
cluster positional errors were manually recovered. The final samples comprise
270 and 355 redMaPPer and X-CLASS clusters respectively. X-ray cluster matching
rates were analysed as a function of optical richness. In a second step, the
redMaPPer clusters were correlated with the entire X-ray catalogue, containing
point and uncharacterised sources (down to a few 10^{-15} erg s^{-1} cm^{-2} in
the [0.5-2] keV band). A stacking analysis was performed for the remaining
undetected optical clusters. Main results show that neither of the wavebands
misses any massive cluster (as coded by X-ray luminosity or optical richness).
After correcting for obvious pipeline short-comings (about 10% of the cases
both in optical and X-ray), ~50% of the redMaPPer (down to a richness of 20)
are found to coincide with an X-CLASS cluster; when considering X-ray sources
of any type, this fraction increases to ~ 80%; for the remaining objects, the
stacking analysis finds a weak signal within 0.5 Mpc around the cluster optical
centers. The fraction of clusters totally dominated by AGN-type emission
appears to be of the order of a few percent. Conversely ~ 40% of the X-CLASS
clusters are identified with a redMaPPer (down to a richness of 20) - part of
the non-matches being due to the fact that the X-CLASS sample extends further
out than redMaPPer (z<1 vs z<0.6); extending the correlation down to a richness
of 5, raises the matching rate to ~ 65%.Comment: 15 pages, 20 figures, 2 table
The Red Sequence Luminosity Function in Massive Intermediate Redshift Galaxy Clusters
We measure the rest-frame B-band luminosity function of red-sequence galaxies
(RSLF) of five intermediate-redshift (0.5 950
km/s) clusters. Cluster galaxies are identified through photometric redshifts
based on imaging in seven bands (five broad, and two narrow) using the WIYN
3.5m telescope. The luminosity functions are well-fit down to M_B^*+3 for all
of the clusters out to a radius of R_200. For comparison, the luminosity
functions for a sample of 59 low redshift clusters selected from the SDSS are
measured as well. There is a brightening trend (M_B^* increases by 0.7 mags by
z=0.75) with redshift comparable to what is seen in the field for similarly
defined galaxies, although there is a hint that the cluster red-sequence
brightening is more rapid in the past (z>0.5), and relatively shallow at more
recent times. Contrary to other claims, we find little evidence for evolution
of the faint end slope. Previous indications of evolution may be due to
limitations in measurement technique, bias in the sample selection, and cluster
to cluster variation. As seen in both the low and high redshift sample, a
significant amount of variation in luminosity functions parameters alpha and
M^* exists between individual clusters.Comment: 40 pages, 14 figures, accepted for publication in the Astrophysical
Journa
Compact Binaries in Star Clusters II - Escapers and Detection Rates
We use a self-consistent Monte Carlo treatment of stellar dynamics to
investigate black hole binaries that are dynamically ejected from globular
clusters to determine if they will be gravitational wave sources. We find that
many of the ejected binaries have initially short periods and will merge within
a Hubble time due to gravitational wave radiation. Thus they are potential
sources for ground-based gravitational wave detectors. We estimate the yearly
detection rate for current and advanced ground-based detectors and find a
modest enhancement over the rate predicted for binaries produced by pure
stellar evolution in galactic fields. We also find that many of the ejected
binaries will pass through the longer wavelength Laser Interferometer Space
Antenna (LISA) band and may be individually resolvable. We find a low
probability that the Galaxy will contain a binary in the LISA band during its
three-year mission. Some such binaries may, however, be detectable at Mpc
distances implying that there may be resolvable stellar-mass LISA sources
beyond our Galaxy. We conclude that globular clusters have a significant effect
on the detection rate of ground-based detectors and may produce interesting
LISA sources in local group galaxies.Comment: 19 pages, 16 figures, 2 tables, submitted to MNRA
The extended ROSAT-ESO Flux Limited X-ray Galaxy Cluster Survey (REFLEX II)\\ II. Construction and Properties of the Survey
Galaxy clusters provide unique laboratories to study astrophysical processes
on large scales and are important probes for cosmology. X-ray observations are
currently the best means of detecting and characterizing galaxy clusters. In
this paper we describe the construction of the REFLEX II galaxy cluster survey
based on the southern part of the ROSAT All-Sky Survey. REFLEX II extends the
REFLEX I survey by a factor of about two down to a flux limit of erg s cm (0.1 - 2.4 keV). We describe the determination
of the X-ray parameters, the process of X-ray source identification, and the
construction of the survey selection function. The REFLEX II cluster sample
comprises currently 915 objects. A standard selection function is derived for a
lower source count limit of 20 photons in addition to the flux limit. The
median redshift of the sample is . Internal consistency checks and
the comparison to several other galaxy cluster surveys imply that REFLEX II is
better than 90\% complete with a contamination less than 10\%.Comment: Astronomy and Astrophysics Vol. 555, A30 - 15 pages, 20 figure
The Northern Sky Optical Cluster Survey II: An Objective Cluster Catalog for 5800 Square Degrees
We present a new, objectively defined catalog of candidate galaxy clusters
based on the galaxy catalogs from the Digitized Second Palomar Observatory Sky
Survey (DPOSS). This cluster catalog, derived from the best calibrated plates
in the high latitude (|b|>30) Northern Galactic Cap region, covers 5,800 square
degrees, and contains 8,155 candidate clusters. A simple adaptive kernel
density mapping technique, combined with the SExtractor object detection
algorithm, is used to detect galaxy overdensities, which we identify as
clusters. Simulations of the background galaxy distribution and clusters of
varying richnesses and redshifts allow us to optimize detection parameters, and
measure the completeness and contamination rates for our catalog. Cluster
richnesses and photometric redshifts are measured, using integrated colors and
magnitudes for each cluster. An extensive spectroscopic survey is used to
confirm the photometric results.
This catalog, with well-characterized sample properties, provides a sound
basis for future studies of cluster physics and large scale structure.Comment: 49 pages, 16 figures. Accepted to AJ; appearing in April. Version
with full resolution figures, and full length tables available at
http://dposs.caltech.edu:8080/NoSOCS.htm
Halo Model Analysis of Cluster Statistics
We use the halo model formalism to provide expressions for cluster abundances
and bias, as well as estimates for the correlation matrix between these
observables. Off-diagonal elements due to scatter in the mass tracer scaling
with mass are included, as are observational effects such as biases/scatter in
the data, detection rates (completeness), and false detections (purity). We
apply the formalism to a hypothetical volume limited optical survey where the
cluster mass tracer is chosen to be the number of member galaxies assigned to a
cluster. Such a survey can strongly constrain
(), the power law index where
(), and perhaps even
the Hubble parameter (). We find cluster abundances and
bias not well suited for constraining or the amplitude . We
also find that without bias information and are degenerate,
implying constraints on the former are strongly dependent on priors used for
the latter and vice-versa. The degeneracy stems from an intrinsic scaling
relation of the halo mass function, and hence it should be present regardless
of the mass tracer used in the survey.Comment: 27 pages, 11 figures, references adde
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