24 research outputs found
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
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
Galaxy clusters discovered via the Sunyaev-Zel'dovich effect in the first 720 square degrees of the South Pole Telescope survey
We present a catalog of 224 galaxy cluster candidates, selected through their
Sunyaev-Zel'dovich (SZ) effect signature in the first 720 deg2 of the South
Pole Telescope (SPT) survey. This area was mapped with the SPT in the 2008 and
2009 austral winters to a depth of 18 uK-arcmin at 150 GHz; 550 deg2 of it was
also mapped to 44 uK-arcmin at 95 GHz. Based on optical imaging of all
candidates and near-infrared imaging of the majority of candidates, we have
found optical and/or infrared counterparts for 158 clusters. Of these, 135 were
first identified as clusters in SPT data, including 117 new discoveries
reported in this work. This catalog triples the number of confirmed galaxy
clusters discovered through the SZ effect. We report photometrically derived
(and in some cases spectroscopic) redshifts for confirmed clusters and redshift
lower limits for the remaining candidates. The catalog extends to high redshift
with a median redshift of z = 0.55 and maximum redshift of z = 1.37. Based on
simulations, we expect the catalog to be nearly 100% complete above M500 ~ 5e14
Msun h_{70}^-1 at z > 0.6. There are 121 candidates detected at signal-to-noise
greater than five, at which the catalog purity is measured to be 95%. From this
high-purity subsample, we exclude the z < 0.3 clusters and use the remaining
100 candidates to improve cosmological constraints following the method
presented by Benson et al., 2011. Adding the cluster data to CMB+BAO+H0 data
leads to a preference for non-zero neutrino masses while only slightly reducing
the upper limit on the sum of neutrino masses to sum mnu < 0.38 eV (95% CL).
For a spatially flat wCDM cosmological model, the addition of this catalog to
the CMB+BAO+H0+SNe results yields sigma8=0.807+-0.027 and w = -1.010+-0.058,
improving the constraints on these parameters by a factor of 1.4 and 1.3,
respectively. [abbrev]Comment: 22 pages, 7 figures, submitted 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
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
A Massive, Cooling-Flow-Induced Starburst in the Core of a Highly Luminous Galaxy Cluster
In the cores of some galaxy clusters the hot intracluster plasma is dense
enough that it should cool radiatively in the cluster's lifetime, leading to
continuous "cooling flows" of gas sinking towards the cluster center, yet no
such cooling flow has been observed. The low observed star formation rates and
cool gas masses for these "cool core" clusters suggest that much of the cooling
must be offset by astrophysical feedback to prevent the formation of a runaway
cooling flow. Here we report X-ray, optical, and infrared observations of the
galaxy cluster SPT-CLJ2344-4243 at z = 0.596. These observations reveal an
exceptionally luminous (L_2-10 keV = 8.2 x 10^45 erg/s) galaxy cluster which
hosts an extremely strong cooling flow (dM/dt = 3820 +/- 530 Msun/yr). Further,
the central galaxy in this cluster appears to be experiencing a massive
starburst (740 +/- 160 Msun/yr), which suggests that the feedback source
responsible for preventing runaway cooling in nearby cool core clusters may not
yet be fully established in SPT-CLJ2344-4243. This large star formation rate
implies that a significant fraction of the stars in the central galaxy of this
cluster may form via accretion of the intracluster medium, rather than the
current picture of central galaxies assembling entirely via mergers.Comment: 11 pages, 3 figures, 1 table. Supplemental material contains 15
additional pages. Published in Natur
Redshifts, Sample Purity, and BCG Positions for the Galaxy Cluster Catalog from the First 720 Square Degrees of the South Pole Telescope Survey
We present the results of the ground- and space-based optical and near-infrared (NIR) follow-up of 224 galaxy cluster candidates detected with the Sunyaev-Zel'dovich (SZ) effect in the 720 deg^2 of the South Pole Telescope (SPT) survey completed in the 2008 and 2009 observing seasons. We use the optical/NIR data to establish whether each candidate is associated with an overdensity of galaxies and to estimate the cluster redshift. Most photometric redshifts are derived through a combination of three different cluster redshift estimators using red-sequence galaxies, resulting in an accuracy of Δz/(1 + z) = 0.017, determined through comparison with a subsample of 57 clusters for which we have spectroscopic redshifts. We successfully measure redshifts for 158 systems and present redshift lower limits for the remaining candidates. The redshift distribution of the confirmed clusters extends to z = 1.35 with a median of z_(med) = 0.57. Approximately 18% of the sample with measured redshifts lies at z > 0.8. We estimate a lower limit to the purity of this SPT SZ-selected sample by assuming that all unconfirmed clusters are noise fluctuations in the SPT data. We show that the cumulative purity at detection significance ξ > 5(ξ > 4.5) is ≥95% (≥70%). We present the red brightest cluster galaxy (rBCG) positions for the sample and examine the offsets between the SPT candidate position and the rBCG. The radial distribution of offsets is similar to that seen in X-ray-selected cluster samples, providing no evidence that SZ-selected cluster samples include a different fraction of recent mergers from X-ray-selected cluster samples
Weak-Lensing Mass Measurements of Five Galaxy Clusters in the South Pole Telescope Survey Using Magellan/Megacam
We use weak gravitational lensing to measure the masses of five galaxy
clusters selected from the South Pole Telescope (SPT) survey, with the primary
goal of comparing these with the SPT Sunyaev--Zel'dovich (SZ) and X-ray based
mass estimates. The clusters span redshifts 0.28 < z < 0.43 and have masses
M_500 > 2 x 10^14 h^-1 M_sun, and three of the five clusters were discovered by
the SPT survey. We observed the clusters in the g'r'i' passbands with the
Megacam imager on the Magellan Clay 6.5m telescope. We measure a mean ratio of
weak lensing (WL) aperture masses to inferred aperture masses from the SZ data,
both within an aperture of R_500,SZ derived from the SZ mass, of 1.04 +/- 0.18.
We measure a mean ratio of spherical WL masses evaluated at R_500,SZ to
spherical SZ masses of 1.07 +/- 0.18, and a mean ratio of spherical WL masses
evaluated at R_500,WL to spherical SZ masses of 1.10 +/- 0.24. We explore
potential sources of systematic error in the mass comparisons and conclude that
all are subdominant to the statistical uncertainty, with dominant terms being
cluster concentration uncertainty and N-body simulation calibration bias.
Expanding the sample of SPT clusters with WL observations has the potential to
significantly improve the SPT cluster mass calibration and the resulting
cosmological constraints from the SPT cluster survey. These are the first WL
detections using Megacam on the Magellan Clay telescope.Comment: Main body: 18 pages, 7 figures, 6 tables. Appendix: 6 pages, 10
figures. Accepted by ApJ. New version incorporates changes from accepted
articl
Loss of ATF2 Function Leads to Cranial Motoneuron Degeneration during Embryonic Mouse Development
The AP-1 family transcription factor ATF2 is essential for development and tissue maintenance in mammals. In particular, ATF2 is highly expressed and activated in the brain and previous studies using mouse knockouts have confirmed its requirement in the cerebellum as well as in vestibular sense organs. Here we present the analysis of the requirement for ATF2 in CNS development in mouse embryos, specifically in the brainstem. We discovered that neuron-specific inactivation of ATF2 leads to significant loss of motoneurons of the hypoglossal, abducens and facial nuclei. While the generation of ATF2 mutant motoneurons appears normal during early development, they undergo caspase-dependent and independent cell death during later embryonic and foetal stages. The loss of these motoneurons correlates with increased levels of stress activated MAP kinases, JNK and p38, as well as aberrant accumulation of phosphorylated neurofilament proteins, NF-H and NF-M, known substrates for these kinases. This, together with other neuropathological phenotypes, including aberrant vacuolisation and lipid accumulation, indicates that deficiency in ATF2 leads to neurodegeneration of subsets of somatic and visceral motoneurons of the brainstem. It also confirms that ATF2 has a critical role in limiting the activities of stress kinases JNK and p38 which are potent inducers of cell death in the CNS
Cosmological Constraints from Sunyaev-Zel'dovich-Selected Clusters with X-ray Observations in the First 178 Square Degrees of the South Pole Telescope Survey
We use measurements from the South Pole Telescope (SPT) Sunyaev Zel'dovich
(SZ) cluster survey in combination with X-ray measurements to constrain
cosmological parameters. We present a statistical method that fits for the
scaling relations of the SZ and X-ray cluster observables with mass while
jointly fitting for cosmology. The method is generalizable to multiple cluster
observables, and self-consistently accounts for the effects of the cluster
selection and uncertainties in cluster mass calibration on the derived
cosmological constraints. We apply this method to a data set consisting of an
SZ-selected catalog of 18 galaxy clusters at z > 0.3 from the first 178 deg2 of
the 2500 deg2 SPT-SZ survey, with 14 clusters having X-ray observations from
either Chandra or XMM. Assuming a spatially flat LCDM cosmological model, we
find the SPT cluster sample constrain sigma_8 (Omega_m/0.25)^0.30 = 0.785 +-
0.037. In combination with measurements of the CMB power spectrum from the SPT
and the seven-year WMAP data, the SPT cluster sample constrain sigma_8 = 0.795
+- 0.016 and Omega_m = 0.255 +- 0.016, a factor of 1.5 improvement on each
parameter over the CMB data alone. We consider several extensions beyond the
LCDM model by including the following as free parameters: the dark energy
equation of state (w), the sum of the neutrino masses (sum mnu), the effective
number of relativistic species (Neff), and a primordial non-Gaussianity (fNL).
We find that adding the SPT cluster data significantly improves the constraints
on w and sum mnu beyond those found when using measurements of the CMB,
supernovae, baryon acoustic oscillations, and the Hubble constant. Considering
each extension independently, we best constrain w=-0.973 +- 0.063 and the sum
of neutrino masses sum mnu < 0.28 eV at 95% confidence, a factor of 1.25 and
1.4 improvement, respectively, over the constraints without clusters. [abbrev.]Comment: 21 pages, 8 figures, submitted to Ap