Galaxy Cluster Catalog Research Articles

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$^2$ of South Pole Telescope (SPT) data. This work represents the complete sample of clusters detected at high significance in the 2500-square-degree SPT-SZ survey, which was completed in 2011. A total of 677 (409) cluster candidates are identified above a signal-to-noise threshold of $\xi$ =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 $\xi$>4.5 candidates and 387 (or 95%) of the $\xi$>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 $M_{\scriptsize 500c}(\rho_\mathrm{crit})$ ~ 3.5 x 10$^{14} M_\odot h^{-1}$, the median redshift is $z_{med}$ =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.

On the dust content of galaxy clusters

We present a study to estimate the dust content in galaxy clusters by using one the most complete existing catalogues of galaxy clusters based on SDSS data and following two methods: the first one compares the colours of samples of galaxies in the background of clusters with those of galaxies in the field. Using this method, we have explored clustercentric distances up to 6 Mpc. The galaxies used in this first method were selected from the SDSS-DR9, among those having reliable photometry and accurate estimation of photometric redshifts. The results are largely independent of the galactic cut applied. At |b|>20 deg., the sample contains 56,985 clusters in the redshift range 0.05<z<0.68 (the mean redshift is 0.30) and ~5.3x10^6 galaxies. The second method computes the contribution of dust in clusters of galaxies to the far infrared sky. That is estimated indirectly by measuring the effect of clusters in the E(B-V) extinction map. Using the first method, we did not find any dependence with clustercentric distance in the colours of background galaxies. This allows us to constrain the mass of dust in the intracluster media, M_dust<8.4x10^9 M_sun (95% C.L.) within a cluster radius of 3 Mpc. With the second method, which averages the extinction of all clusters, we find a surface integral of the excess of colour g-i of 3.4+/-0.1 millimag Mpc^2. This is equivalent to ~60 times the far infrared luminosity of a Milky Way-like galaxy. By assumming similar properties for the dust, we can estimate a total dust mass per cluster of ~2x10^9 M_sun, which is compatible with the hypothesis that the dust is within the spiral galaxies of a cluster. Separating the clusters in 5x5 bins in redshift and richness, we confirm previous findings of a clear increase in luminosity with a redshift that agrees with the trend expected from current models.

The Adopted Morphological Types of 247 Rich PF Galaxy Clusters

AbstractMorphological types were determined for 247 rich galaxy clusters from the PF Catalogue of Galaxy Clusters and Groups. The adopted types are based on classical morphological schemes and consider concentration to the cluster center, the signs of preferential direction or plane in the cluster, and the positions of the brightest galaxies. It is shown that both concentration and preferential plane are significant and independent morphological criteria.

Flux- and volume-limited groups/clusters for the SDSS galaxies: catalogues and mass estimation

We provide flux-limited and volume-limited galaxy group and cluster catalogues, based on the spectroscopic sample of the SDSS data release 10 galaxies. We used a modified friends-of-friends (FoF) method with a variable linking length in the transverse and radial directions to identify as many realistic groups as possible. The flux-limited catalogue incorporates galaxies down to m_r = 17.77 mag. It includes 588193 galaxies and 82458 groups. The volume-limited catalogues are complete for absolute magnitudes down to M_r = -18.0, -18.5, -19.0, -19.5, -20.0, -20.5, and -21.0; the completeness is achieved within different spatial volumes, respectively. Our analysis shows that flux-limited and volume-limited group samples are well compatible to each other, especially for the larger groups/clusters. Dynamical mass estimates, based on radial velocity dispersions and group extent in the sky, are added to the extracted groups. The catalogues can be accessed via http://cosmodb.to.ee and the Strasbourg Astronomical Data Center (CDS).

Towards a better understanding of galaxy clusters

AbstractObservational data on clusters of galaxies holds relevant information that can be used to determine the relative plausibility of different models for the large-scale evolution of the Universe, or estimate the joint posterior probability distribution function of the parameters that pertain to each model. Within the next few years, several surveys of the sky will yield large galaxy cluster catalogues. In order to make use of the vast amount of information they will contain, their selection functions will have to be properly understood. We argue this, as well as the estimation of the full joint posterior probability distribution function of the most relevant cluster properties, can be best achieved in the framework of bayesian statistics.

A phenomenological model for the intracluster medium that matches X-ray and Sunyaev–Zel'dovich observations

Cosmological hydrodynamical simulations of galaxy clusters are still challenged to produce a model for the intracluster medium that matches all aspects of current X-ray and Sunyaev-Zel'dovich observations. To facilitate such comparisons with future simulations and to enable realistic cluster population studies for modeling e.g., non-thermal emission processes, we construct a phenomenological model for the intracluster medium that is based on a representative sample of observed X-ray clusters. We create a mock galaxy cluster catalog based on the large collisionless N-body simulation MultiDark, by assigning our gas density model to each dark matter cluster halo. Our clusters are classified as cool-core and non cool-core according to a dynamical disturbance parameter. We demonstrate that our gas model matches the various observed Sunyaev-Zel'dovich and X-ray scaling relations as well as the X-ray luminosity function, thus enabling to build a reliable mock catalog for present surveys and forecasts for future experiments. In a companion paper, we apply our catalogs to calculate non-thermal radio and gamma-ray emission of galaxy clusters. We make our cosmologically complete multi-frequency mock catalogs for the (non-)thermal cluster emission at different redshifts publicly and freely available online through the MultiDark database (www.multidark.org).

On the physics of radio haloes in galaxy clusters: scaling relations and luminosity functions

The underlying physics of giant and mini radio haloes in galaxy clusters is still an open question. We find that mini haloes (such as in Perseus and Ophiuchus) can be explained by radio-emitting electrons that are generated in hadronic cosmic ray (CR) interactions with protons of the intracluster medium. By contrast, the hadronic model either fails to explain the extended emission of giant radio haloes (as in Coma at low frequencies) or would require a flat CR profile, which can be realized through outward streaming and diffusion of CRs (in Coma and A2163 at 1.4 GHz). We suggest that a second leptonic component could be responsible for the missing flux in the outer parts of giant haloes within a new hybrid scenario and we describe its possible observational consequences. To study the hadronic emission component of the radio-halo population statistically, we use a cosmological mock galaxy cluster catalogue built from the MultiDark simulation. Because of the properties of CR streaming and the different scalings of the X-ray luminosity (LX) and the Sunyaev–Zel'dovich flux (Y) with gas density, our model can simultaneously reproduce the observed bimodality of radio-loud and radio-quiet clusters at the same LX as well as the unimodal distribution of radio-halo luminosity versus Y; thereby suggesting a physical solution to this apparent contradiction. We predict radio-halo emission down to the mass scale of galaxy groups, which highlights the unique prospects for low-frequency radio surveys (such as the Low Frequency Array Tier 1 survey) to increase the number of detected radio haloes by at least an order of magnitude.

Measuring the thermal Sunyaev-Zel'dovich effect through the cross correlation of Planck and WMAP maps with ROSAT galaxy cluster catalogs

We measure a significant correlation between the thermal Sunyaev-Zel'dovich effect in the Planck and WMAP maps and an X-ray cluster map based on ROSAT. We use the 100, 143 and 343 GHz Planck maps and the WMAP 94 GHz map to obtain this cluster cross spectrum. We check our measurements for contamination from dusty galaxies using the cross correlations with the 217, 545 and 857 GHz maps from Planck. Our measurement yields a direct characterization of the cluster power spectrum over a wide range of angular scales that is consistent with large cosmological simulations. The amplitude of this signal depends on cosmological parameters that determine the growth of structure (σ8 and ΩM) and scales as σ87.4 and ΩM1.9 around the multipole (ℓ) ∼ 1000. We constrain σ8 and ΩM from the cross-power spectrum to be σ8(ΩM/0.30)0.26 = 0.8±0.02. Since this cross spectrum produces a tight constraint in the σ8 and ΩM plane the errors on a σ8 constraint will be mostly limited by the uncertainties from external constraints. Future cluster catalogs, like those from eRosita and LSST, and pointed multi-wavelength observations of clusters will improve the constraining power of this cross spectrum measurement. In principle this analysis can be extended beyond σ8 and ΩM to constrain dark energy or the sum of the neutrino masses.

Overview of photometric galaxy cluster surveys at optical wavelengths

The first galaxy cluster catalog was constructed by Abell in the 50s. Since then, with the advent of multi-megapixel digital cameras mounted on telescopes all over the world there have been a variety of optical photometric surveys with the ambituous goal to map out the large scale structure of the universe to larger and larger redshifts. One goal of these large scale structure surveys has been the discovery of thousands of galaxy clusters which have been used for a variety of cosmological and astrophysical studies. We shall review the salient features of these galaxy cluster surveys in the past two decades and provide a brief snapshot of some of the upcoming surveys in the next decade.

Neutrino mass from future large scale structure surveys

We examine whether future, nearly all-sky spectroscopic galaxy surveys and photometric galaxy-cluster catalogs, as the ESA Euclid satellite, in combination with CMB priors, will be able to detect the signature of the cosmic neutrino background and determine the absolute neutrino mass scale. We find that the sensitivity of such future surveys is well suited to span the entire range of neutrino masses allowed by neutrino oscillation experiments, and to yield a clear detection of non-zero neutrino mass.

A comparison of algorithms for the construction of SZ cluster catalogues

We evaluate the construction methodology of an all-sky catalogue of galaxy clusters detected through the Sunyaev-Zel'dovich (SZ) effect. We perform an extensive comparison of twelve algorithms applied to the same detailed simulations of the millimeter and submillimeter sky based on a Planck-like case. We present the results of this "SZ Challenge" in terms of catalogue completeness, purity, astrometric and photometric reconstruction. Our results provide a comparison of a representative sample of SZ detection algorithms and highlight important issues in their application. In our study case, we show that the exact expected number of clusters remains uncertain (about a thousand cluster candidates at |b|> 20 deg with 90% purity) and that it depends on the SZ model and on the detailed sky simulations, and on algorithmic implementation of the detection methods. We also estimate the astrometric precision of the cluster candidates which is found of the order of ~2 arcmins on average, and the photometric uncertainty of order ~30%, depending on flux.

ONE THOUSAND AND ONE CLUSTERS: MEASURING THE BULK FLOW WITH THE PLANCK ESZ AND X-RAY-SELECTED GALAXY CLUSTER CATALOGS

We present our measurement of the "bulk flow" using the kinetic Sunyaev-Zel'dovich (kSZ) effect in the WMAP 7-year data. As the tracer of peculiar velocities, we use Planck Early Sunyaev-Zel'dovich Detected Cluster Catalog and a compilation of X-ray detected galaxy cluster catalogs based on ROSAT All-Sky Survey. We build a full-sky kSZ template and fit it to the WMAP data in W-band. Using a Wiener filter we maximize the signal to noise ratio of the kSZ cluster signal in the data. We find no significant detection of the bulk flow, and our results are consistent with the LCDM prediction.

Constructing mock catalogues for the REFLEX II galaxy cluster sample

We describe the construction of a suite of galaxy cluster mock catalogues from N-body simulations, based on the properties of the new ROSAT–ESO Flux Limited X-Ray (REFLEX II) galaxy cluster catalogue. Our procedure is based on the measurements of the cluster abundance, and involves the calibration of the underlying scaling relation linking the mass of dark matter haloes to the cluster X-ray luminosity determined in the ROSAT energy band 0.1–2.4keV. In order to reproduce the observed abundance in the luminosity range probed by the REFLEX II X-ray luminosity function [0.01 < LX/(1044ergs−1h−2) < 10], a mass–X-ray luminosity relation deviating from a simple power law is required. We discuss the dependence of the calibration of this scaling relation on the X-ray luminosity and the definition of halo masses and analyse the one- and two-point statistical properties of the mock catalogues. Our set of mock catalogues provides samples with self-calibrated scaling relations of galaxy clusters together with inherent properties of flux-limited surveys. This makes them a useful tool to explore different systematic effects and statistical methods involved in constraining both astrophysical and cosmological information from present and future galaxy cluster surveys.

THE MASS-RICHNESS RELATION OF MaxBCG CLUSTERS FROM QUASAR LENSING MAGNIFICATION USING VARIABILITY

Accurate measurement of galaxy cluster masses is an essential component not only in studies of cluster physics, but also for probes of cosmology. However, different mass measurement techniques frequently yield discrepant results. The SDSS MaxBCG catalog's mass-richness relation has previously been constrained using weak lensing shear, Sunyaev-Zeldovich (SZ), and X-ray measurements. The mass normalization of the clusters as measured by weak lensing shear is >~25% higher than that measured using SZ and X-ray methods, a difference much larger than the stated measurement errors in the analyses. We constrain the mass-richness relation of the MaxBCG galaxy cluster catalog by measuring the gravitational lensing magnification of type I quasars in the background of the clusters. The magnification is determined using the quasars' variability and the correlation between quasars' variability amplitude and intrinsic luminosity. The mass-richness relation determined through magnification is in agreement with that measured using shear, confirming that the lensing strength of the clusters implies a high mass normalization, and that the discrepancy with other methods is not due to a shear-related systematic measurement error. We study the dependence of the measured mass normalization on the cluster halo orientation. As expected, line-of-sight clusters yield a higher normalization; however, this minority of haloes does not significantly bias the average mass-richness relation of the catalog.

How many radio relics await discovery?

Upcoming radio telescopes will allow to study the radio sky at low frequencies with unprecedent sensitivity and resolution. New surveys are expected to discover a large number of new radio sources. Here we investigate the abundance of radio relics, i.e. steep-spectrum diffuse radio emission coming from the periphery of galaxy clusters, which are believed to trace shock waves induced by cluster mergers. With the advent of comprehensive relic samples a framework is needed to analyze statistically the relic abundance. To this end, we introduce the probability to find a relic located in a galaxy cluster with given mass and redshift allowing us to relate the halo mass function of the Universe with the radio relic number counts. Up to date about 45 relics have been reported and we compile the resulting counts, N(>S_1.4). In principle, the parameters of the distribution could be determined using a sufficiently large relic sample. However, since the number of known relics is still small for that purpose we use the MareNostrum Universe simulation to determine the relic radio power scaling with cluster mass and redshift. Our model is able to reproduce the recently found tentative evidence for an increase in the fraction of clusters hosting relics, both with X-ray luminosity and redshift, using an X-ray flux limited cluster sample. Moreover, we find that a considerable fraction of faint relics (S_1.4 < ~10 mJy) reside in clusters with an X-ray flux below ~3e-12 erg/s/cm^2. Finally, we estimate the number of radio relics which await discovery by future low frequency surveys proposed for LOFAR and WSRT. We estimate that the WODAN survey proposed for WSRT may discover 900 relics and that the LOFAR-Tier 1-120 MHz survey may discover about 2500 relics. However, the actual number of newly discovered relics will crucially depend on the existence of sufficiently complete galaxy cluster catalogues.

THE FIRST PUBLIC RELEASE OF SOUTH POLE TELESCOPE DATA: MAPS OF A 95 deg2FIELD FROM 2008 OBSERVATIONS

The South Pole Telescope (SPT) has nearly completed a 2500-square-degree survey of the southern sky in three frequency bands. Here we present the first public release of SPT maps and associated data products. We present arcminute-resolution maps at 150 GHz and 220 GHz of an approximately 95-square-degree field centered at R.A. 82.7 degrees, decl. -55 degrees. The field was observed to a depth of approximately 17 micro-K arcmin at 150 GHz and 41 micro-K arcmin at 220 GHz during the 2008 austral winter season. Two variations on map filtering and map projection are presented, one tailored for producing catalogs of galaxy clusters detected through their Sunyaev-Zel'dovich effect signature and one tailored for producing catalogs of emissive sources. We describe the data processing pipeline, and we present instrument response functions, filter transfer functions, and map noise properties. All data products described in this paper are available for download at http://pole.uchicago.edu/public/data/maps/ra5h30dec-55 and from the NASA Legacy Archive for Microwave Background Data Analysis server. This is the first step in the eventual release of data from the full 2500-square-degree SPT survey.

The 2XMMi/SDSS Galaxy Cluster Survey

We present a catalogue of X-ray selected galaxy clusters and groups as a first release of the 2XMMi/SDSS Galaxy Cluster Survey. The survey is a search for galaxy clusters detected serendipitously in observations with XMM-Newton in the footprint of the Sloan Digital Sky Survey (SDSS). The main aims of the survey are to identify new X-ray galaxy clusters, investigate their X-ray scaling relations, identify distant cluster candidates and study the correlation of the X-ray and optical properties. In this paper we describe the basic strategy to identify and characterize the X-ray cluster candidates that currently comprise 1180 objects selected from the second XMM-Newton serendipitous source catalogue (2XMMi-DR3). Cross-correlation of the initial catalogue with recently published optically selected SDSS galaxy cluster catalogues yields photometric redshifts for 275 objects. Of these, 182 clusters have at least one member with a spectroscopic redshift from existing public data (SDSS-DR8). Here we present the X-ray properties of the first cluster sample which comprises 175 clusters, among which 139 objects are new X-ray discoveries while the others were previously known as X-ray sources. The first cluster sample from the survey covers a wide range of redshifts from 0.09 to 0.61, bolometric luminosities L_500 = 1.9 x 10^42 - 1.2 x 10^45 erg/s, and masses M_500 = 2.3 x 10^13 - 4.9 x 10^14 Msun. We extend the relation between the X-ray bolometric luminosity L_500 and the X-ray temperature towards significantly lower T and L and still find that the slope of the linear L-T relation is consistent with values published for high luminosities.

X-ray calibration of Sunyaev-Zel’dovich scaling relations with the ACCEPT catalogue of galaxy clusters observed by Chandra

We explore the scaling relation between the flux of the Sunyaev-Zel'dovich (SZ) effect and the total mass of galaxy clusters using already reduced Chandra X-ray data present in the ACCEPT (Archive of Chandra Cluster Entropy Profile Tables) catalogue. The analysis is conducted over a sample of 226 objects, examining the relatively small scale corresponding to a cluster overdensity equal to 2500 times the critical density of the background universe, at which the total masses have been calculated exploiting the hydrostatic equilibrium hypothesis. Core entropy (K0) is strongly correlated with the central cooling time, and is therefore used to identify cooling-core (CC) objects in our sample. Our results confirm the self-similarity of the scaling relation between the integrated Comptonization parameter (Y) and the cluster mass, for both CC and NCC (non-cooling-core) clusters. The consistency of our calibration with recent ones has been checked, with further support for Y as a good mass proxy. We also investigate the robustness of the constant gas fraction assumption, for fixed overdensity, and of the Yx proxy (Kravstov et al. 2007) considering CC and NCC clusters, again sorted on K0 from our sample. We extend our study to implement a K0-proxy, obtained by combining SZ and X-ray observables, which is proposed to provide a CC indicator for higher redshift objects. Finally, we suggest that an SZ-only CC indicator could benefit from the employment of deprojected Comptonization radial profiles.

Friends-of-friends groups and clusters in the 2SLAQ catalogue

We present a catalogue of galaxy groups and clusters selected using a friends-of-friends algorithm with a dynamic linking length from the 2dF-SDSS and QSO (2SLAQ) luminous red galaxy survey. The linking parameters for the code are chosen through an analysis of simulated 2SLAQ haloes. The resulting catalogue includes 313 clusters containing 1,152 galaxies. The galaxy groups and clusters have an average velocity dispersion of sigma_v = 467.97 km/s and an average size of R_clt = 0.78 Mpc/h. Galaxies from regions of one square degree and centred on the galaxy clusters were downloaded from the Sloan Digital Sky Survey Data Release 6 (SDSS DR6). Investigating the photometric redshifts and cluster red-sequence of these galaxies shows that the galaxy clusters detected with the FoF algorithm are reliable out to z~0.6. We estimate masses for the clusters using their velocity dispersions. These mass estimates are shown to be consistent with 2SLAQ mock halo masses. Further analysis of the simulation haloes shows that clipping out low richness groups with large radii improves the purity of catalogue from 52% to 88%, while retaining a completeness of 94%. Finally, we test the two-point correlation function of our cluster catalogue. We find a best-fitting power law model with parameters r0 = 24\pm4 Mpc/h and gamma = -2.1\pm 0.2, which are in agreement with other low redshift cluster samples and consistent with a {\Lambda}CDM universe.

Galaxy Superclusters Detected in the Modified PF-Catalog Using the FOF Method

Abstract The Modified Catalog of Galaxy Clusters and Groups (Panko &amp; Flin 2006, PF), covering an area of 5000 square degrees in the southern sky, was used as the input for the search of galaxy superclusters. Only the estimated redshifts could be used, since the PF catalog is a 2D catalog, with the calibration correlating the redshift of galaxy clusters with the magnitude of the tenth brightest cluster galaxy. Only galaxy clusters containing more than 50 galaxies were considered, and the FoF method was applied. The nearest neighbour distances for 1711 input clusters were calculated and analyzed, and 20 isolated clusters were found with the nearest neighbour at a distance greater than 68 h-1Mpc. A distance of 24 h-1 Mpc between clusters was selected for the supercluster search, and 49 superclusters containing from 4 to 9 galaxy clusters were detected. Calculations for each supercluster include: its inferred center, RA, Dec, zest, the maximum distance between supercluster members and the estimated supercluster shapes. A typical size of superclusters identified here is about 55 h-1 Mpc, and they appear mainly as elongated pancakes, with a weak correlation between the axes c/a and b/a, without a strong dependence on multiplicity.