118 research outputs found
GALAXY CLUSTERS DISCOVERED VIA THE SUNYAEV-ZEL'DOVICH EFFECT IN THE 2500-SQUARE-DEGREE SPT-SZ SURVEY
We present a catalog of galaxy clusters selected via their Sunyaev-Zel'dovich (SZ) effect signature from 2500 deg[superscript 2] of South Pole Telescope (SPT) data. This work represents the complete sample of clusters detected at high significance in the 2500 deg[superscript 2] SPT-SZ survey, which was completed in 2011. A total of 677 (409) cluster candidates are identified above a signal-to-noise threshold of ξ = 4.5 (5.0). Ground- and space-based optical and near-infrared (NIR) imaging confirms overdensities of similarly colored galaxies in the direction of 516 (or 76%) of the ξ > 4.5 candidates and 387 (or 95%) of the ξ > 5 candidates; the measured purity is consistent with expectations from simulations. Of these confirmed clusters, 415 were first identified in SPT data, including 251 new discoveries reported in this work. We estimate photometric redshifts for all candidates with identified optical and/or NIR counterparts; we additionally report redshifts derived from spectroscopic observations for 141 of these systems. The mass threshold of the catalog is roughly independent of redshift above z ~ 0.25 leading to a sample of massive clusters that extends to high redshift. The median mass of the sample is M [subscript 500c](ρ[subscript crit]) ~ 3.5 x 10[superscript 14] M[subscript ʘ] h[-1 over 70], the median redshift is z [subscript med] = 0.55, and the highest-redshift systems are at z > 1.4. The combination of large redshift extent, clean selection, and high typical mass makes this cluster sample of particular interest for cosmological analyses and studies of cluster formation and evolution
A MEASUREMENT OF GRAVITATIONAL LENSING OF THE COSMIC MICROWAVE BACKGROUND BY GALAXY CLUSTERS USING DATA FROM THE SOUTH POLE TELESCOPE
Clusters of galaxies are expected to gravitationally lens the cosmic microwave background (CMB) and thereby generate a distinct signal in the CMB on arcminute scales. Measurements of this effect can be used to constrain the masses of galaxy clusters with CMB data alone. Here we present a measurement of lensing of the CMB by galaxy clusters using data from the South Pole Telescope (SPT). We develop a maximum likelihood approach to extract the CMB cluster lensing signal and validate the method on mock data. We quantify the effects on our analysis of several potential sources of systematic error and find that they generally act to reduce the best-fit cluster mass. It is estimated that this bias to lower cluster mass is roughly 0.85σ in units of the statistical error bar, although this estimate should be viewed as an upper limit. We apply our maximum likelihood technique to 513 clusters selected via their Sunyaev–Zeldovich (SZ) signatures in SPT data, and rule out the null hypothesis of no lensing at 3.1σ. The lensing-derived mass estimate for the full cluster sample is consistent with that inferred from the SZ flux: M[subscript 200,lens] = 0.83[+0.38 over -0.37] M[subscript 200,SZ] (68% C.L., statistical error only)
An HST/WFC3-UVIS View of the Starburst in the Cool Core of the Phoenix Cluster
We present Hubble Space Telescope Wide Field Camera 3 observations of the
core of the Phoenix Cluster SPT-CLJ2344-4243 in five broadband filters spanning
rest-frame 1000--5500A. These observations reveal complex, filamentary blue
emission, extending for >40kpc from the brightest cluster galaxy. We observe an
underlying, diffuse population of old stars, following an r^1/4 distribution,
confirming that this system is somewhat relaxed. The spectral energy
distribution in the inner part of the galaxy, as well as along the extended
filaments, is a smooth continuum and is consistent with that of a star-forming
galaxy, suggesting that the extended, filamentary emission is not due to the
central AGN, either from a large-scale ionized outflow or scattered polarized
UV emission, but rather a massive population of young stars. We estimate an
extinction-corrected star formation rate of 798 +/- 42 Msun/yr, consistent with
our earlier work based on low spatial resolution ultraviolet, optical, and
infrared imaging. The lack of tidal features and multiple bulges, combine with
the need for an exceptionally massive (>10^11 Msun) cold gas reservoir, suggest
that this star formation is not the result of a merger of gas-rich galaxies.
Instead, we propose that the high X-ray cooling rate of ~2700 Msun/yr is the
origin of the cold gas reservoir. The combination of such a high cooling rate
and the relatively weak radio source in the cluster core suggests that feedback
has been unable to halt cooling in this system, leading to this tremendous
burst of star formation.Comment: 7 pages, 5 figures, accepted for publication in ApJ Letter
The Outer Limits of Galaxy Clusters: Observations to the Virial Radius with Suzaku, XMM, and Chandra
The outskirts of galaxy clusters, near the virial radius, remain relatively
unexplored territory and yet are vital to our understanding of cluster growth,
structure, and mass. In this presentation, we show the first results from a
program to constrain the state of the outer intracluster medium (ICM) in a
large sample of galaxy clusters, exploiting the strengths of three
complementary X-ray observatories: Suzaku (low, stable background), XMM-Newton
(high sensitivity), and Chandra (good spatial resolution). By carefully
combining observations from the cluster core to beyond r_200, we are able to
identify and reduce systematic uncertainties that would impede our spatial and
spectral analysis using a single telescope. Our sample comprises nine clusters
at z ~ 0.1-0.2 fully covered in azimuth to beyond r_200, and our analysis
indicates that the ICM is not in hydrostatic equilibrium in the cluster
outskirts, where we see clear azimuthal variations in temperature and surface
brightness. In one of the clusters, we are able to measure the diffuse X-ray
emission well beyond r_200, and we find that the entropy profile and the gas
fraction are consistent with expectations from theory and numerical
simulations. These results stand in contrast to recent studies which point to
gas clumping in the outskirts; the extent to which differences of cluster
environment or instrumental effects factor in this difference remains unclear.
From a broader perspective, this project will produce a sizeable fiducial data
set for detailed comparison with high-resolution numerical simulations.Comment: 8 pages, 6 figures. To appear in the proceedings of the Suzaku 2011
Conference, "Exploring the X-ray Universe: Suzaku and Beyond.
The Complicated Evolution of the ACIS Contamination Layer over the Mission Life of the Chandra X-ray Observatory
The Chandra X-ray Observatory was launched almost 19 years ago and has been
delivering spectacular science over the course of its mission. The Advanced CCD
Imager Spectrometer is the prime instrument on the satellite, conducting over
90% of the observations. The CCDs operate at a temperature of -120 C and the
optical blocking filter in front of the CCDs is at a temperature of
approximately -60C. The surface of the OBF has accumulated a layer of
contamination over the course of the mission. We have been characterizing the
thickness, chemical composition, and spatial distribution of the contamination
layer as a function of time over the mission. All three have exhibited
significant changes with time. There has been a dramatic decrease in the
accumulation rate of the contaminant starting in 2017. The lower accumulation
rate may be due to a decrease in the deposition rate or an increase in the
vaporization rate or a combination of the two. We show that the current
calibration file which models the additional absorption of the contamination
layer is significantly overestimating that additional absorption by using the
standard model spectrum for the supernova remnant 1E 0102.2-7219 developed by
the International Astronomical Consortium for High Energy Calibration. In
addition, spectral data from the cluster of galaxies known as Abell 1795 and
the Blazar Markarian 421 are used to generate a model of the absorption
produced by the contamination layer. The Chandra X-ray Center calibration team
is preparing a revised calibration file that more accurately represents the
complex time dependence of the accumulation rate, the spatial dependence, and
the chemical composition of the contaminant. Given the rapid changes in the
contamination layer over the past year, future calibration observations at a
higher cadence will be necessary to more accurately monitor such changes.Comment: 15 pages, 10 figures, SPIE Astronomical Instruments and Telescopes
2018, Conference Series, 1069
Hitomi Constraints on the 3.5 keV Line in the Perseus Galaxy Cluster
High-resolution X-ray spectroscopy with Hitomi was expected to resolve the origin of the faint unidentified E 3.5 ≈ keV emission line reported in several low-resolution studies of various massive systems, such as galaxies and clusters, including the Perseus cluster. We have analyzed the Hitomi first-light observation of the Perseus cluster. The emission line expected for Perseus based on the XMM-Newton signal from the large cluster sample under the dark matter decay scenario is too faint to be detectable in the Hitomi data. However, the previously reported 3.5 keV flux from Perseus was anomalously high compared to the sample-based prediction. We find no unidentified line at the reported high flux level. Taking into account the XMM measurement uncertainties for this region, the inconsistency with Hitomi is at a 99% significance for a broad dark matter line and at 99.7% for a narrow line from the gas. We do not find anomalously high fluxes of the nearby faint K line or the Ar satellite line that were proposed as explanations for the earlier 3.5 keV detections. We do find a hint of a broad excess near the energies of high-n transitions of S xvi E 3.44 ≃ keV rest-frame)—a possible signature of charge exchange in the molecular nebula and another proposed explanation for the unidentified line. While its energy is consistent with XMM pn detections, it is unlikely to explain the MOS signal. A confirmation of this interesting feature has to wait for a more sensitive observation with a future calorimeter experiment.United States. National Aeronautics and Space Administration. Science Mission DirectorateUnited States. Department of Energy (Lawrence Livermore National Laboratory. Contract DE-AC52- 07NA27344
Gas Clumping in the Outskirts of Galaxy Clusters, an Assessment of the Sensitivity of STAR-X
In the outskirts of galaxy clusters, entropy profiles measured from X-ray
observations of the hot intracluster medium (ICM) drops off unexpectedly. One
possible explanation for this effect is gas clumping, where pockets of cooler
and denser structures within the ICM are present. Current observatories are
unable to directly detect these hypothetical gas clumps. One of the science
drivers of the proposed STAR-X observatory is to resolve these or similar
structures. Its high spatial resolution, large effective area, and low
instrumental background make STAR-X ideal for directly detecting and
characterizing clumps and diffuse emission in cluster outskirts. The aim of
this work is to simulate observations of clumping in clusters to determine how
well STAR-X will be able to detect clumps, as well as what clumping properties
reproduce observed entropy profiles. This is achieved by using yt, pyXSIM,
SOXS, and other tools to inject ideally modeled clumps into three-dimensional
models derived from actual clusters using their observed profiles from other
X-ray missions. Radial temperature and surface brightness profiles are then
extracted from mock observations using concentric annuli. We find that in
simulated observations for STAR-X, a parameter space of clump properties exists
where gas clumps can be successfully identified using wavdetect and masked, and
are able to recover the true cluster profiles. This demonstrates that STAR-X
could be capable of detecting substructure in the outskirts of nearby clusters
and that the properties of both the outskirts and the clumps will be revealed.Comment: This is a pre-copyedited, author-produced PDF of an article accepted
for publication in RAS Techniques and Instruments (RASTI) following peer
review. The version of record is available online at:
https://academic.oup.com/rasti/article/doi/10.1093/rasti/rzad042/725882
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