- ID:
- ivo://CDS.VizieR/J/A+A/471/17
- Title:
- SDSS-DR4 nearby clusters global properties
- Short Name:
- J/A+A/471/17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Large surveys such as the Sloan Digital Sky Survey have made large amounts of spectroscopic and photometric data of galaxies available, thereby providing important information for studying galaxy evolution in dense environments. We have selected a sample of 88 nearby (z<0.1) galaxy clusters from the SDSS-DR4 with redshift information for the cluster members. In particular, we focus on the galaxy morphological distribution, the velocity dispersion profiles, and the fraction of blue galaxies in clusters. Cluster membership was determined using the available velocity information. We derived global properties for each cluster, such as their mean recessional velocity, velocity dispersion, and virial radii. Cluster galaxies were grouped into two families according to their u-r colours.
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- ID:
- ivo://CDS.VizieR/J/ApJS/244/22
- Title:
- SDSS DR8 redMaPPer clusters Chandra follow-up
- Short Name:
- J/ApJS/244/22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In order to place constraints on cosmology through optical surveys of galaxy clusters, one must first understand the properties of those clusters. To this end, we introduce the Mass Analysis Tool for Chandra (MATCha), a pipeline that uses a parallellized algorithm to analyze archival Chandra data. MATCha simultaneously calculates X-ray temperatures and luminosities and performs centering measurements for hundreds of potential galaxy clusters using archival X-ray exposures. We run MATCha on the redMaPPer SDSS DR8 cluster catalog and use MATCha's output X-ray temperatures and luminosities to analyze the galaxy cluster temperature-richness, luminosity-richness, luminosity-temperature, and temperature-luminosity scaling relations. We detect 447 clusters and determine 246 r_2500_ temperatures across all redshifts. Within 0.1<z<0.35, we find that r_2500_ T_X_ scales with optical richness ({lambda}) as ln(k_B_T_X_/1.0keV)=(0.52+/-0.05)ln({lambda}/70)+(1.85+/-0.03) with an intrinsic scatter of 0.27+/-0.02 (1{sigma}). We investigate the distribution of offsets between the X-ray center and redMaPPer center within 0.1<z<0.35, finding that 68.3%+/-6.5% of clusters are well-centered. However, we find a broad tail of large offsets in this distribution, and we explore some of the causes of redMaPPer miscentering.
- ID:
- ivo://CDS.VizieR/J/A+A/539/A80
- Title:
- SDSS DR7 superclusters. The catalogues
- Short Name:
- J/A+A/539/A80
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have constructed a set of supercluster catalogues for the galaxies from the SDSS survey main and luminous red galaxy (LRG) flux-limited samples. To delineate superclusters, we calculated luminosity density fields using the B_3_-spline kernel of the radius of 8Mpc/h for the main sample and 16Mpc/h for the LRG sample and define regions with densities over a selected threshold as superclusters, while utilising almost the whole volume of both samples. We created two types of catalogues, one with an adaptive local threshold and a set of catalogues with different global thresholds. We describe the supercluster catalogues and their general properties. Using smoothed bootstrap, we find uncertainty estimates for the density field and use these to attribute confidence levels to the catalogue objects. We have also created a test catalogue for the galaxies from the Millennium simulation to compare the simulated and observed superclusters and to clarify the methods we use. We find that the superclusters are well-defined systems, and the properties of the superclusters of the main and LRG samples are similar. We also show that with adaptive local thresholds we get a sample of superclusters, the properties of which do not depend on their distance from the observer. The Millennium galaxy catalogue superclusters are similar to those observed.
- ID:
- ivo://CDS.VizieR/J/MNRAS/440/1248
- Title:
- SDSS DR7 voids and superclusters
- Short Name:
- J/MNRAS/440/1248
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The study of the interesting cosmological properties of voids in the Universe depends on the efficient and robust identification of such voids in galaxy redshift surveys. Recently, Sutter et al. have published a public catalogue of voids in the Sloan Digital Sky Survey Data Release 7 main galaxy and luminous red galaxy samples, using the void-finding algorithm ZOBOV, which is based on the watershed transform. We examine the properties of this catalogue and show that it suffers from several problems and inconsistencies, including the identification of some extremely overdense regions as voids. As a result, cosmological results obtained using this catalogue need to be reconsidered. We provide instead an alternative, self-consistent, public catalogue of voids in the same galaxy data, obtained from using an improved version of the same watershed transform algorithm. We provide a more robust method of dealing with survey boundaries and masks, as well as with a radially varying selection function, which means that our method can be applied to any other survey. We discuss some basic properties of the voids thus discovered, and describe how further information may be obtained from the catalogue. In addition, we apply an inversion of the algorithm to the same data to obtain a corresponding catalogue of large-scale overdense structures, or `superclusters'. Our catalogues are available for public download on the journal website.
- ID:
- ivo://CDS.VizieR/J/AJ/123/1807
- Title:
- SDSS galaxy clusters redshifts
- Short Name:
- J/AJ/123/1807
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe an automated method, the cut-and-enhance (CE) method, for detecting clusters of galaxies in multicolor optical imaging surveys. This method uses simple color cuts, combined with a density enhancement algorithm, to up-weight pairs of galaxies that are close in both angular separation and color. The method is semiparametric, since it uses minimal assumptions about cluster properties in order to minimize possible biases. No assumptions are made about the shape of clusters, their radial profile, or their luminosity function. The method is successful in finding systems ranging from poor to rich clusters of galaxies, of both regular and irregular shape. We determine the selection function of the CE method via extensive Monte Carlo simulations that use both the real, observed background of galaxies and a randomized background of galaxies. We use position-shuffled and color-shuffled data to perform false-positive tests. We have also visually checked all the clusters detected by the CE method. We apply the CE method to the 350{deg}^2^ of the Sloan Digital Sky Survey (SDSS) commissioning data, taken in 1998 September and 1999 March, and construct an SDSS CE galaxy cluster catalog with an estimated redshift and richness for each cluster. The CE method is compared with other cluster selection methods used on SDSS data such as the matched filter, "maxBCG," and Voronoi tessellation techniques. The CE method can be adopted for cluster selection in any multicolor imaging survey.
- ID:
- ivo://CDS.VizieR/J/ApJ/769/52
- Title:
- SDSS luminous red galaxies concentrations
- Short Name:
- J/ApJ/769/52
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The best gravitational lenses for detecting distant galaxies are those with the largest mass concentrations and the most advantageous configurations of that mass along the line of sight. Our new method for finding such gravitational telescopes uses optical data to identify projected concentrations of luminous red galaxies (LRGs). LRGs are biased tracers of the underlying mass distribution, so lines of sight with the highest total luminosity in LRGs are likely to contain the largest total mass. We apply this selection technique to the Sloan Digital Sky Survey and identify the 200 fields with the highest total LRG luminosities projected within a 3.5' radius over the redshift range 0.1<=z<=0.7. The redshift and angular distributions of LRGs in these fields trace the concentrations of non-LRG galaxies. These fields are diverse; 22.5% contain one known galaxy cluster and 56.0% contain multiple known clusters previously identified in the literature. Thus, our results confirm that these LRGs trace massive structures and that our selection technique identifies fields with large total masses. These fields contain two to three times higher total LRG luminosities than most known strong-lensing clusters and will be among the best gravitational lensing fields for the purpose of detecting the highest redshift galaxies.
- ID:
- ivo://CDS.VizieR/J/AJ/121/2331
- Title:
- SDSS redshifts in the Coma cluster
- Short Name:
- J/AJ/121/2331
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- On 1999 May 26, one of the Sloan Digital Sky Survey (SDSS) fiber-fed spectrographs saw astronomical first light. This was followed by the first spectroscopic commissioning run during the dark period of 1999 June. We present here the first hour of extragalactic spectroscopy taken during these early commissioning stages: an observation of the Coma cluster of galaxies. Our data samples the southern part of this cluster, out to a radius of 15{deg} (1.8h^-1^Mpc, approximately to the virial radius) and thus fully covers the NGC 4839 group. We provide redshifts and spectral classifications for 196 Coma galaxies, of which 45 redshifts are new. For the 151 galaxies in common with the literature, we find excellent agreement between our redshift determinations and the published values, e.g., for the largest homogeneous sample of galaxies in common (63 galaxies observed by Colless & Dunn, 1996ApJ...458..435C) we find a mean offset of 3km/s and an rms scatter of only 24km/s.
- ID:
- ivo://CDS.VizieR/J/ApJ/662/224
- Title:
- Second CIZA subsample
- Short Name:
- J/ApJ/662/224
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the latest results of the Clusters in the Zone of Avoidance (CIZA) survey, which is mapping large-scale structures behind the Milky Way by performing the first systematic search for galaxy clusters at low Galactic latitudes. The survey's approach, which uses X-ray emission to locate cluster candidates, minimizes the problems faced by optically selected cluster surveys, which have traditionally avoided this region of the sky due to the severe extinction present along the Galactic plane. We here present the second flux-limited CIZA cluster catalog, containing 57 X-ray-selected galaxy clusters, of which 88% are new discoveries. We use this sample to examine the degree to which known large-scale structures extend into the zone of avoidance and highlight newly discovered structures that have previously gone unnoticed.
- ID:
- ivo://CDS.VizieR/J/ApJ/694/992
- Title:
- SED of cluster radio galaxies
- Short Name:
- J/ApJ/694/992
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To explore the high-frequency radio spectra of galaxies in clusters, we used NRAO's Very Large Array at four frequencies, 4.9-43GHz, to observe 139 galaxies in low redshift (z<0.25), X-ray detected, clusters. The clusters were selected from the survey conducted by Ledlow and Owen (1997ApJS..108...41O), who provided redshifts and 1.4GHz flux densities for all the radio sources. We find that more than half of the observed sources have steep microwave spectra as generally expected ({alpha}<-0.5, in the convention S{proto}{nu}^{alpha}^). However, 60%-70% of the unresolved or barely resolved sources have flat or inverted spectra. Most of these show an upward turn in flux at {nu}>22GHz, implying a higher flux than would be expected from an extrapolation of the lower-frequency flux measurements. Our results quantify the need for careful source subtraction in increasingly sensitive measurements of the Sunyaev-Zel'dovich effect in clusters of galaxies (as currently being conducted by, for instance, the Atacama Cosmology Telescope and South Pole Telescope groups).
- ID:
- ivo://CDS.VizieR/J/ApJ/729/22
- Title:
- SEDs of galaxy cluster members
- Short Name:
- J/ApJ/729/22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from a study of AGNs and their host galaxies found in low-redshift galaxy clusters. We fit model spectral energy distributions (SEDs) to the combined visible and mid-infrared (MIR) photometry of cluster members and use these model SEDs to determine stellar masses and star formation rates (SFRs). We identify two populations of AGNs, the first based on their X-ray luminosities (X-ray AGNs) and the second based on the presence of a significant AGN component in their model SEDs (IR AGNs). We find that the two AGN populations are nearly disjoint; only 8 out of 44 AGNs are identified with both techniques.
