36 research outputs found
Optical followup of galaxy clusters detected by the South Pole Telescope
The South Pole Telescope (SPT) is a 10 meter telescope operating at mm
wavelengths. It has recently completed a three-band survey covering 2500 sq.
degrees. One of the survey's main goals is to detect galaxy clusters using
Sunyaev-Zeldovich effect and use these clusters for a variety of cosmological
and astrophysical studies such as the dark energy equation of state, the
primordial non-gaussianity and the evolution of galaxy populations. Since 2005,
we have been engaged in a comprehensive optical and near-infrared followup
program (at wavelengths between 0.4 and 5 {\mu}m) to image high-significance
SPT clusters, to measure their photometric redshifts, and to estimate the
contamination rate of the candidate lists. These clusters are then used for
various cosmological and astrophysical studies.Comment: For TAUP 2011 proceeding
Detection of X-ray galaxy clusters based on the Kolmogorov method
The detection of clusters of galaxies in large surveys plays an important
part in extragalactic astronomy, and particularly in cosmology, since cluster
counts can give strong constraints on cosmological parameters. X-ray imaging is
in particular a reliable means to discover new clusters, and large X-ray
surveys are now available. Considering XMM-Newton data for a sample of 40 Abell
clusters, we show that their analysis with a Kolmogorov distribution can
provide a distinctive signature for galaxy clusters. The Kolmogorov method is
sensitive to the correlations in the cluster X-ray properties and can therefore
be used for their identification, thus allowing to search reliably for clusters
in a simple way
A Multiband Study of the Galaxy Populations of the First Four Sunyaev--Zeldovich Effect selected Galaxy Clusters
We present first results of an examination of the optical properties of the
galaxy populations in SZE selected galaxy clusters. Using clusters selected by
the South Pole Telescope survey and deep multiband optical data from the Blanco
Cosmology Survey, we measure the radial profile, the luminosity function, the
blue fraction and the halo occupation number of the galaxy populations of these
four clusters with redshifts ranging from 0.3 to 1. Our goal is to understand
whether there are differences among the galaxy populations of these SZE
selected clusters and previously studied clusters selected in the optical and
the X-ray. The radial distributions of galaxies in the four systems are
consistent with NFW profiles with a galaxy concentration of 3 to 6. We show
that the characteristic luminosities in bands are consistent with
passively evolving populations emerging from a single burst at redshift .
The faint end power law slope of the luminosity function is found to be on
average in griz. Halo occupation numbers (to ) for
these systems appear to be consistent with those based on X-ray selected
clusters. The blue fraction estimated to , for the three lower
redshift systems, suggests an increase with redshift, although with the current
sample the uncertainties are still large. Overall, this pilot study of the
first four clusters provides no evidence that the galaxy populations in these
systems differ significantly from those in previously studied cluster
populations selected in the X-ray or the optical.Comment: 12 pages, 12 figures and 3 tables. Accepted for publication in Ap
South Pole Telescope Detections of the Previously Unconfirmed Planck Early SZ Clusters in the Southern Hemisphere
We present South Pole Telescope (SPT) observations of the five galaxy cluster
candidates in the southern hemisphere which were reported as unconfirmed in the
Planck Early Sunyaev-Zel'dovich (ESZ) sample. One cluster candidate, PLCKESZ
G255.62-46.16, is located in the 2500-square-degree SPT SZ survey region and
was reported previously as SPT-CL J0411-4819. For the remaining four
candidates, which are located outside of the SPT SZ survey region, we performed
short, dedicated SPT observations. Each of these four candidates was strongly
detected in maps made from these observations, with signal-to-noise ratios
ranging from 6.3 to 13.8. We have observed these four candidates on the
Magellan-Baade telescope and used these data to estimate cluster redshifts from
the red sequence. Resulting redshifts range from 0.24 to 0.46. We report
measurements of Y_0.75', the integrated Comptonization within a 0.75' radius,
for all five candidates. We also report X-ray luminosities calculated from
ROSAT All-Sky Survey catalog counts, as well as optical and improved SZ
coordinates for each candidate. The combination of SPT SZ measurements, optical
red-sequence measurements, and X-ray luminosity estimates demonstrates that
these five Planck ESZ cluster candidates do indeed correspond to real galaxy
clusters with redshifts and observable properties consistent with the rest of
the ESZ sample.Comment: 7 emulateapj pages, 4 figures, 1 table. Revised to match published
versio
SPT-CL J0546-5345: A Massive z > 1 Galaxy Cluster Selected Via the Sunyaev-Zel'dovich Effect with the South Pole Telescope
We report the spectroscopic confirmation of SPT-CL J0546-5345 at = 1.067.
To date this is the most distant cluster to be spectroscopically confirmed from
the 2008 South Pole Telescope (SPT) catalog, and indeed the first z > 1 cluster
discovered by the Sunyaev-Zel'dovich Effect (SZE). We identify 21 secure
spectroscopic members within 0.9 Mpc of the SPT cluster position, 18 of which
are quiescent, early-type galaxies. From these quiescent galaxies we obtain a
velocity dispersion of 1179^{+232}_{-167} km/s, ranking SPT-CL J0546-5345 as
the most dynamically massive cluster yet discovered at z > 1. Assuming that
SPT-CL J0546-5345 is virialized, this implies a dynamical mass of M_200 =
1.0^{+0.6}_{-0.4} x 10^{15} Msun, in agreement with the X-ray and SZE mass
measurements. Combining masses from several independent measures leads to a
best-estimate mass of M_200 = (7.95 +/- 0.92) x 10^{14} Msun. The spectroscopic
confirmation of SPT-CL J0546-5345, discovered in the wide-angle, mass-selected
SPT cluster survey, marks the onset of the high redshift SZE-selected galaxy
cluster era.Comment: ApJ, in pres
Galaxy Clusters Selected with the Sunyaev-Zel'dovich Effect from 2008 South Pole Telescope Observations
We present a detection-significance-limited catalog of 21 Sunyaev-Zel'dovich
selected galaxy clusters. These clusters, along with 1 unconfirmed candidate,
were identified in 178 deg^2 of sky surveyed in 2008 by the South Pole
Telescope to a depth of 18 uK-arcmin at 150 GHz. Optical imaging from the
Blanco Cosmology Survey (BCS) and Magellan telescopes provided photometric (and
in some cases spectroscopic) redshift estimates, with catalog redshifts ranging
from z=0.15 to z>1, with a median z = 0.74. Of the 21 confirmed galaxy
clusters, three were previously identified as Abell clusters, three were
presented as SPT discoveries in Staniszewski et al, 2009, and three were first
identified in a recent analysis of BCS data by Menanteau et al, 2010; the
remaining 12 clusters are presented for the first time in this work. Simulated
observations of the SPT fields predict the sample to be nearly 100% complete
above a mass threshold of M_200 ~ 5x10^14 M_sun/h at z = 0.6. This completeness
threshold pushes to lower mass with increasing redshift, dropping to ~4x10^14
M_sun/h at z=1. The size and redshift distribution of this catalog are in good
agreement with expectations based on our current understanding of galaxy
clusters and cosmology. In combination with other cosmological probes, we use
the cluster catalog to improve estimates of cosmological parameters. Assuming a
standard spatially flat wCDM cosmological model, the addition of our catalog to
the WMAP 7-year analysis yields sigma_8 = 0.81 +- 0.09 and w = -1.07 +- 0.29, a
~50% improvement in precision on both parameters over WMAP7 alone.Comment: 19 pages, 9 figures, 4 appendice
SPT-CL J0205-5829: A z = 1.32 Evolved Massive Galaxy Cluster in the South Pole Telescope Sunyaev-Zel'dovich Effect Survey
The galaxy cluster SPT-CL J0205-5829 currently has the highest
spectroscopically-confirmed redshift, z=1.322, in the South Pole Telescope
Sunyaev-Zel'dovich (SPT-SZ) survey. XMM-Newton observations measure a
core-excluded temperature of Tx=8.7keV producing a mass estimate that is
consistent with the Sunyaev-Zel'dovich derived mass. The combined SZ and X-ray
mass estimate of M500=(4.9+/-0.8)e14 h_{70}^{-1} Msun makes it the most massive
known SZ-selected galaxy cluster at z>1.2 and the second most massive at z>1.
Using optical and infrared observations, we find that the brightest galaxies in
SPT-CL J0205-5829 are already well evolved by the time the universe was <5 Gyr
old, with stellar population ages >3 Gyr, and low rates of star formation
(<0.5Msun/yr). We find that, despite the high redshift and mass, the existence
of SPT-CL J0205-5829 is not surprising given a flat LambdaCDM cosmology with
Gaussian initial perturbations. The a priori chance of finding a cluster of
similar rarity (or rarer) in a survey the size of the 2500 deg^2 SPT-SZ survey
is 69%.Comment: 11 pages, 5 figures, submitted to Ap
SPT-CLJ2040-4451: An SZ-Selected Galaxy Cluster at z = 1.478 With Significant Ongoing Star Formation
SPT-CLJ2040-4451 -- spectroscopically confirmed at z = 1.478 -- is the
highest redshift galaxy cluster yet discovered via the Sunyaev-Zel'dovich
effect. SPT-CLJ2040-4451 was a candidate galaxy cluster identified in the first
720 deg^2 of the South Pole Telescope Sunyaev-Zel'dovich (SPT-SZ) survey, and
confirmed in follow-up imaging and spectroscopy. From multi-object spectroscopy
with Magellan-I/Baade+IMACS we measure spectroscopic redshifts for 15 cluster
member galaxies, all of which have strong [O II] 3727 emission.
SPT-CLJ2040-4451 has an SZ-measured mass of M_500,SZ = 3.2 +/- 0.8 X 10^14
M_Sun/h_70, corresponding to M_200,SZ = 5.8 +/- 1.4 X 10^14 M_Sun/h_70. The
velocity dispersion measured entirely from blue star forming members is sigma_v
= 1500 +/- 520 km/s. The prevalence of star forming cluster members (galaxies
with > 1.5 M_Sun/yr) implies that this massive, high-redshift cluster is
experiencing a phase of active star formation, and supports recent results
showing a marked increase in star formation occurring in galaxy clusters at z
>1.4. We also compute the probability of finding a cluster as rare as this in
the SPT-SZ survey to be >99%, indicating that its discovery is not in tension
with the concordance Lambda-CDM cosmological model.Comment: 14 pages, 8 figures, 4 tables, Accepted to Ap
The Growth of Cool Cores and Evolution of Cooling Properties in a Sample of 83 Galaxy Clusters at 0.3 < z < 1.2 Selected from the SPT-SZ Survey
We present first results on the cooling properties derived from Chandra X-ray
observations of 83 high-redshift (0.3 < z < 1.2) massive galaxy clusters
selected by their Sunyaev-Zel'dovich signature in the South Pole Telescope
data. We measure each cluster's central cooling time, central entropy, and mass
deposition rate, and compare to local cluster samples. We find no significant
evolution from z~0 to z~1 in the distribution of these properties, suggesting
that cooling in cluster cores is stable over long periods of time. We also find
that the average cool core entropy profile in the inner ~100 kpc has not
changed dramatically since z ~ 1, implying that feedback must be providing
nearly constant energy injection to maintain the observed "entropy floor" at
~10 keV cm^2. While the cooling properties appear roughly constant over long
periods of time, we observe strong evolution in the gas density profile, with
the normalized central density (rho_0/rho_crit) increasing by an order of
magnitude from z ~ 1 to z ~ 0. When using metrics defined by the inner surface
brightness profile of clusters, we find an apparent lack of classical, cuspy,
cool-core clusters at z > 0.75, consistent with earlier reports for clusters at
z > 0.5 using similar definitions. Our measurements indicate that cool cores
have been steadily growing over the 8 Gyr spanned by our sample, consistent
with a constant, ~150 Msun/yr cooling flow that is unable to cool below
entropies of 10 keV cm^2 and, instead, accumulates in the cluster center. We
estimate that cool cores began to assemble in these massive systems at z ~ 1,
which represents the first constraints on the onset of cooling in galaxy
cluster cores. We investigate several potential biases which could conspire to
mimic this cool core evolution and are unable to find a bias that has a similar
redshift dependence and a substantial amplitude.Comment: 17 pages with 15 figures, plus appendix. Published in Ap
Optical Spectroscopy and Velocity Dispersions of Galaxy Clusters from the SPT-SZ Survey
We present optical spectroscopy of galaxies in clusters detected through the
Sunyaev-Zel'dovich (SZ) effect with the South Pole Telescope (SPT). We report
our own measurements of spectroscopic cluster redshifts, and velocity
dispersions each calculated with more than member galaxies. This catalog
also includes dispersions of SPT-observed clusters previously reported in
the literature. The majority of the clusters in this paper are SPT-discovered;
of these, most have been previously reported in other SPT cluster catalogs, and
five are reported here as SPT discoveries for the first time. By performing a
resampling analysis of galaxy velocities, we find that unbiased velocity
dispersions can be obtained from a relatively small number of member galaxies
(), but with increased systematic scatter. We use this analysis to
determine statistical confidence intervals that include the effect of
membership selection. We fit scaling relations between the observed cluster
velocity dispersions and mass estimates from SZ and X-ray observables. In both
cases, the results are consistent with the scaling relation between velocity
dispersion and mass expected from dark-matter simulations. We measure a
30% log-normal scatter in dispersion at fixed mass, and a 10%
offset in the normalization of the dispersion-mass relation when compared to
the expectation from simulations, which is within the expected level of
systematic uncertainty.Comment: Accepted to ApJ. 20 pages, 6 figure