- 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.
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Search Results
- 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.
- ID:
- ivo://CDS.VizieR/J/MNRAS/464/183
- Title:
- Segregation effects in DEEP2 galaxy groups
- Short Name:
- J/MNRAS/464/183
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate segregation phenomena in galaxy groups in the range of 0.2<z<1. We study a sample of groups selected from the 4th Data Release of the DEEP2 galaxy redshift survey. We used only groups with at least eight members within a radius of 4 Mpc. Outliers were removed with the shifting gapper technique and, then, the virial properties were estimated for each group. The sample was divided into two stacked systems: low(z<=0.6) and high (z>0.6) redshift groups. Assuming that the colour index (U-B)_0_ can be used as a proxy for the galaxy type, we found that the fraction of blue (star-forming) objects is higher in the high-z sample, with blue objects being dominant at M_B_>-19.5 for both samples, and red objects being dominant at M_B_<-19.5 only for the low-z sample. Also, the radial variation of the red fraction indicates that there are more red objects with R<R_200_ in the low-z sample than in the high-z sample. Our analysis indicates statistical evidence of kinematic segregation, at the 99 per cent c.l., for the low-z sample: redder and brighter galaxies present lower velocity dispersions than bluer and fainter ones. We also find a weaker evidence for spatial segregation between red and blue objects, at the 70 per cent c.l. The analysis of the high-z sample reveals a different result: red and blue galaxies have velocity dispersion distributions not statistically distinct, although redder objects are more concentrated than the bluer ones at the 95 per cent c.l. From the comparison of blue/red and bright/faint fractions, and considering the approximate lookback time-scale between the two samples (~3Gyr), our results are consistent with a scenario where bright red galaxies had time to reach energy equipartition, while faint blue/red galaxies in the outskirts infall to the inner parts of the groups, thus reducing spatial segregation from z~0.8 to z~0.4.
- ID:
- ivo://CDS.VizieR/J/MNRAS/453/3729
- Title:
- Sersic + exponential disc morphologies in Coma
- Short Name:
- J/MNRAS/453/3729
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Galaxies are not limited to simple spheroid or bulge + disc morphologies. We explore the diversity of internal galaxy structures in the Coma Cluster across a wide range of luminosities (-17>Mg>-22) and cluster-centric radii (0<r_cluster_<1.3r_200_) through analysis of deep Canada-France-Hawaii Telescope i-band imaging. We present 2D multicomponent decomposition via galfit, encompassing a wide range of candidate model morphologies with up to three photometric components. Particular focus is placed on early-type galaxies with outer discs (i.e. S0s), and deviations from simple ('unbroken') exponential discs. Rigorous filtering ensures that each model component provides a statistically significant improvement to the goodness-of-fit. The majority of Coma Cluster members in our sample (478 of 631) are reliably fitted by symmetric structural models. Of these, 134 (28 percent) are single Sersic objects, 143 (30 percent) are well-described by 2-component structures, while 201 (42 percent) require more complex models. Multicomponent Sersic galaxies resemble compact pseudo-bulges (n~2, R_e_~4kpc) surrounded by extended Gaussian-like outer structures (R_e_>10kpc). 11 percent of galaxies (N=52) feature a break in their outer profiles, indicating 'truncated' or 'antitruncated' discs. Beyond the break radius, truncated galaxies are structurally consistent with exponential discs, disfavouring physical truncation as their formation mechanism. Bulge luminosity in antitruncated galaxies correlates strongly with galaxy luminosity, indicating a bulge-enhancing origin for these systems. Both types of broken disc are found overwhelmingly (>70 percent) in 'barred' galaxies, despite a low measured bar fraction for Coma (20+/-2 percent). Thus, galaxy bars play an important role in formation of broken disc structures. No strong variation in galaxy structure is detected with projected cluster-centric radius.
- ID:
- ivo://CDS.VizieR/J/MNRAS/444/L63
- Title:
- SFRs of Brightest Cluster Galaxies
- Short Name:
- J/MNRAS/444/L63
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the mid-infrared star formation rates of 245 X-ray selected, nearby (z<0.1) brightest cluster galaxies (BCGs). A homogeneous and volume limited sample of BCGs was created by X-ray selecting clusters with Lx>1x10^44^erg/s. The Wide-Field Infrared Survey Explorer (WISE) All WISE Data Release provides the first measurement of the 12{mu}m star formation indicator for all BCGs in the nearby Universe. Perseus A and Cygnus A are the only galaxies in our sample to have star formation rates of >40M_{sun}_/yr, indicating that these two galaxies are highly unusual at current times. Stellar populations of 99+/-0.6 per cent of local BCGs are (approximately) passively evolving, with star formation rates of <10M_{sun}_/yr. We find that in general, star formation produces only modest BCG growth at the current epoch.
- ID:
- ivo://CDS.VizieR/VII/196
- Title:
- Shakhbazian compact groups of galaxies
- Short Name:
- VII/196
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The largest survey of compact galaxy groups was published by Shakhbazian et al. (see cat. <VII/89>). This catalogue provides accurate positions of individual galaxies in the groups; photometrical properties of the Southern sky (delta not greater than +2{deg}30') are evaluated on the basis of the COSMOS/UKST catalog of the Southern sky. The catalogue contains 373 groups; this number differs from the number in Shakhbazian's list (377 groups) by the following: => No data for groups 001 (there were already published data by other authors), 206 (could not be re-identified) 241 (could not be re-identified) 252 (is identical with 214), 301 (could not be re-identified) 353 (could not be re-identified) => Group 328 was published twice (in North and South) => Group 340 was divided in two parts (340 and 340a), according to Bettoni and Fasano ([BF95]=1995AJ....109...32B)
