299 research outputs found
The Mean and Scatter of the Velocity Dispersion-Optical Richness Relation for maxBCG Galaxy Clusters
The distribution of galaxies in position and velocity around the centers of
galaxy clusters encodes important information about cluster mass and structure.
Using the maxBCG galaxy cluster catalog identified from imaging data obtained
in the Sloan Digital Sky Survey, we study the BCG-galaxy velocity correlation
function. By modeling its non-Gaussianity, we measure the mean and scatter in
velocity dispersion at fixed richness. The mean velocity dispersion increases
from 202+/-10 km/s for small groups to more than 854+/-102 km/s for large
clusters. We show the scatter to be at most 40.5+/-3.5%, declining to
14.9+/-9.4% in the richest bins. We test our methods in the C4 cluster catalog,
a spectroscopic cluster catalog produced from the Sloan Digital Sky Survey DR2
spectroscopic sample, and in mock galaxy catalogs constructed from N-body
simulations. Our methods are robust, measuring the scatter to well within
one-sigma of the true value, and the mean to within 10%, in the mock catalogs.
By convolving the scatter in velocity dispersion at fixed richness with the
observed richness space density function, we measure the velocity dispersion
function of the maxBCG galaxy clusters. Although velocity dispersion and
richness do not form a true mass-observable relation, the relationship between
velocity dispersion and mass is theoretically well characterized and has low
scatter. Thus our results provide a key link between theory and observations up
to the velocity bias between dark matter and galaxies.Comment: 25 pages, 15 figures, 2 tables, published in Ap
Cross-correlation Weak Lensing of SDSS galaxy Clusters II: Cluster Density Profiles and the Mass--Richness Relation
We interpret and model the statistical weak lensing measurements around
130,000 groups and clusters of galaxies in the Sloan Digital Sky Survey
presented by Sheldon et al. 2007 (Paper I). We present non-parametric
inversions of the 2D shear profiles to the mean 3D cluster density and mass
profiles in bins of both optical richness and cluster i-band luminosity. We
correct the inferred 3D profiles for systematic effects, including non-linear
shear and the fact that cluster halos are not all precisely centered on their
brightest galaxies. We also model the measured cluster shear profile as a sum
of contributions from the brightest central galaxy, the cluster dark matter
halo, and neighboring halos. We infer the relations between mean cluster virial
mass and optical richness and luminosity over two orders of magnitude in
cluster mass; the virial mass at fixed richness or luminosity is determined
with a precision of 13% including both statistical and systematic errors. We
also constrain the halo concentration parameter and halo bias as a function of
cluster mass; both are in good agreement with predictions of LCDM models. The
methods employed here will be applicable to deeper, wide-area optical surveys
that aim to constrain the nature of the dark energy, such as the Dark Energy
Survey, the Large Synoptic Survey Telescope and space-based surveys
Cross-correlation Weak Lensing of SDSS Galaxy Clusters III: Mass-to-light Ratios
We present measurements of the excess mass-to-light ratio measured
aroundMaxBCG galaxy clusters observed in the SDSS. This red sequence cluster
sample includes objects from small groups with masses ranging from ~5x10^{12}
to ~10^{15} M_{sun}/h. Using cross-correlation weak lensing, we measure the
excess mass density profile above the universal mean \Delta \rho(r) = \rho(r) -
\bar{\rho} for clusters in bins of richness and optical luminosity. We also
measure the excess luminosity density \Delta l(r) = l(r) - \bar{l} measured in
the z=0.25 i-band. For both mass and light, we de-project the profiles to
produce 3D mass and light profiles over scales from 25 kpc/ to 22 Mpc/h. From
these profiles we calculate the cumulative excess mass M(r) and excess light
L(r) as a function of separation from the BCG. On small scales, where \rho(r)
>> \bar{\rho}, the integrated mass-to-light profile may be interpreted as the
cluster mass-to-light ratio. We find the M/L_{200}, the mass-to-light ratio
within r_{200}, scales with cluster mass as a power law with index 0.33+/-0.02.
On large scales, where \rho(r) ~ \bar{\rho}, the M/L approaches an asymptotic
value independent of cluster richness. For small groups, the mean M/L_{200} is
much smaller than the asymptotic value, while for large clusters it is
consistent with the asymptotic value. This asymptotic value should be
proportional to the mean mass-to-light ratio of the universe . We find
/b^2_{ml} = 362+/-54 h (statistical). There is additional uncertainty in
the overall calibration at the ~10% level. The parameter b_{ml} is primarily a
function of the bias of the L <~ L_* galaxies used as light tracers, and should
be of order unity. Multiplying by the luminosity density in the same bandpass
we find \Omega_m/b^2_{ml} = 0.02+/-0.03, independent of the Hubble parameter.Comment: Third paper in a series; v2.0 incorporates ApJ referee's suggestion
Cross-correlation Weak Lensing of SDSS Galaxy Clusters I: Measurements
This is the first in a series of papers on the weak lensing effect caused by
clusters of galaxies in Sloan Digital Sky Survey. The photometrically selected
cluster sample, known as MaxBCG, includes ~130,000 objects between redshift 0.1
and 0.3, ranging in size from small groups to massive clusters. We split the
clusters into bins of richness and luminosity and stack the surface density
contrast to produce mean radial profiles. The mean profiles are detected over a
range of scales, from the inner halo (25 kpc/h) well into the surrounding large
scale structure (30 Mpc/h), with a significance of 15 to 20 in each bin. The
signal over this large range of scales is best interpreted in terms of the
cluster-mass cross-correlation function. We pay careful attention to sources of
systematic error, correcting for them where possible. The resulting signals are
calibrated to the ~10% level, with the dominant remaining uncertainty being the
redshift distribution of the background sources. We find that the profiles
scale strongly with richness and luminosity. We find the signal within a given
richness bin depends upon luminosity, suggesting that luminosity is more
closely correlated with mass than galaxy counts. We split the samples by
redshift but detect no significant evolution. The profiles are not well
described by power laws. In a subsequent series of papers we invert the
profiles to three-dimensional mass profiles, show that they are well fit by a
halo model description, measure mass-to-light ratios and provide a cosmological
interpretation.Comment: Paper I in a series; v2.0 includes ApJ referee's suggestion
Precision Measurements of the Cluster Red Sequence using an Error Corrected Gaussian Mixture Model
The red sequence is an important feature of galaxy clusters and plays a
crucial role in optical cluster detection. Measurement of the slope and scatter
of the red sequence are affected both by selection of red sequence galaxies and
measurement errors. In this paper, we describe a new error corrected Gaussian
Mixture Model for red sequence galaxy identification. Using this technique, we
can remove the effects of measurement error and extract unbiased information
about the intrinsic properties of the red sequence. We use this method to
select red sequence galaxies in each of the 13,823 clusters in the maxBCG
catalog, and measure the red sequence ridgeline location and scatter of each.
These measurements provide precise constraints on the variation of the average
red galaxy populations in the observed frame with redshift. We find that the
scatter of the red sequence ridgeline increases mildly with redshift, and that
the slope decreases with redshift. We also observe that the slope does not
strongly depend on cluster richness. Using similar methods, we show that this
behavior is mirrored in a spectroscopic sample of field galaxies, further
emphasizing that ridgeline properties are independent of environment.Comment: 33 pages, 14 Figures; A typo in Eq.A11 is fixed. The C++/Python codes
for ECGMM can be downloaded from:
https://sites.google.com/site/jiangangecgmm
SDSS-RASS: Next Generation of Cluster-Finding Algorithms
We outline here the next generation of cluster-finding algorithms. We show
how advances in Computer Science and Statistics have helped develop robust,
fast algorithms for finding clusters of galaxies in large multi-dimensional
astronomical databases like the Sloan Digital Sky Survey (SDSS). Specifically,
this paper presents four new advances: (1) A new semi-parametric algorithm -
nicknamed ``C4'' - for jointly finding clusters of galaxies in the SDSS and
ROSAT All-Sky Survey databases; (2) The introduction of the False Discovery
Rate into Astronomy; (3) The role of kernel shape in optimizing cluster
detection; (4) A new determination of the X-ray Cluster Luminosity Function
which has bearing on the existence of a ``deficit'' of high redshift, high
luminosity clusters. This research is part of our ``Computational
AstroStatistics'' collaboration (see Nichol et al. 2000) and the algorithms and
techniques discussed herein will form part of the ``Virtual Observatory''
analysis toolkit.Comment: To appear in Proceedings of MPA/MPE/ESO Conference "Mining the Sky",
July 31 - August 4, 2000, Garching, German
MaxBCG: A Red Sequence Galaxy Cluster Finder
Measurements of galaxy cluster abundances, clustering properties, and mass
to- light ratios in current and future surveys can provide important
cosmological constraints. Digital wide-field imaging surveys, the
recently-demonstrated fidelity of red-sequence cluster detection techniques,
and a new generation of realistic mock galaxy surveys provide the means for
construction of large, cosmologicallyinteresting cluster samples, whose
selection and properties can be understood in unprecedented depth. We present
the details of the "maxBCG" algorithm, a cluster-detection technique tailored
to multi-band CCD-imaging data. MaxBCG primarily relies on an observational
cornerstone of massive galaxy clusters: they are marked by an overdensity of
bright, uniformly red galaxies. This detection scheme also exploits classical
brightest cluster galaxies (BCGs), which are often found at the center of these
same massive clusters. (ABRIDGED)Comment: 39 pages, 16 figures, 1 table. Accepted to Ap
Constraining the Scatter in the Mass-Richness Relation of maxBCG Clusters With Weak Lensing and X-ray Data
We measure the logarithmic scatter in mass at fixed richness for clusters in
the maxBCG cluster catalog, an optically selected cluster sample drawn from
SDSS imaging data. Our measurement is achieved by demanding consistency between
available weak lensing and X-ray measurements of the maxBCG clusters, and the
X-ray luminosity--mass relation inferred from the 400d X-ray cluster survey, a
flux limited X-ray cluster survey. We find \sigma_{\ln
M|N_{200}}=0.45^{+0.20}_{-0.18} (95% CL) at N_{200} ~ 40, where N_{200} is the
number of red sequence galaxies in a cluster. As a byproduct of our analysis,
we also obtain a constraint on the correlation coefficient between \ln Lx and
\ln M at fixed richness, which is best expressed as a lower limit, r_{L,M|N} >=
0.85 (95% CL). This is the first observational constraint placed on a
correlation coefficient involving two different cluster mass tracers. We use
our results to produce a state of the art estimate of the halo mass function at
z=0.23 -- the median redshift of the maxBCG cluster sample -- and find that it
is consistent with the WMAP5 cosmology. Both the mass function data and its
covariance matrix are presented.Comment: 14 pages, 6 figures, submitted to Ap
Cosmological Constraints from SDSS maxBCG Cluster Abundances
We perform a maximum likelihood analysis of the cluster abundance measured in
the SDSS using the maxBCG cluster finding algorithm. Our analysis is aimed at
constraining the power spectrum normalization , and assumes flat
cosmologies with a scale invariant spectrum, massless neutrinos, and CMB and
supernova priors Omega_m*h^2=0.128+/-0.01 and h=0.72+/-0.05 respectively.
Following the method described in the companion paper Rozo et al. 2007, we
derive \sigma_8=0.92+/-0.10$ (1-sigma) after marginalizing over all major
systematic uncertainties. We place strong lower limits on the normalization,
sigma_8>0.76 (95% CL) (>0.68 at 99% CL). We also find that our analysis favors
relatively low values for the slope of the Halo Occupation Distribution (HOD),
alpha=0.83+/-0.06. The uncertainties of these determinations will substantially
improve upon completion of an ongoing campaign to estimate dynamical, weak
lensing, and X-ray cluster masses in the SDSS maxBCG cluster sample.Comment: 10 pages, 6 figures, ApJ Submitte
Dust accretion and destruction in galaxy groups and clusters
We examine the dust distribution around a sample of 70,000 low redshift
galaxy groups and clusters derived from the Sloan Digital Sky Survey. By
correlating spectroscopically identified background quasars with the galaxy
groups we obtain the relative colour excess due to dust reddening. We present a
significant detection of dust out to a clustercentric distance of 30 Mpc/h in
all four independent SDSS colours, consistent with the expectations of weak
lensing masses of similar mass halos and excess galaxy counts. The wavelength
dependence of this colour excess is consistent with the expectations of a Milky
Way dust law with R_V=3.1. Further, we find that the halo mass dependence of
the dust content is much smaller than would be expected by a simple scaling,
implying that the dust-to-gas ratio of the most massive clusters (~10E14
Msun/h) is ~3% of the local ISM value, while in small groups (~10E12.7 Msun/h)
it is ~55% of the local ISM value. We also find that the dust must have a
covering fraction on the order of 10% to explain the observed color
differences, which means the dust is not just confined to the most massive
galaxies. Comparing the dust profile with the excess galaxy profile, we find
that the implied dust-to-galaxy ratio falls significantly towards the group or
cluster center. This has a significant halo mass dependence, such that the more
massive groups and clusters show a stronger reduction. This suggests that
either dust is destroyed by thermal sputtering of the dust grains by the hot,
dense gas or the intrinsic dust production is reduced in these galaxies.Comment: 10 pages, MNRAS, in pres
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