- ID:
- ivo://CDS.VizieR/J/ApJ/511/595
- Title:
- An X-Ray Survey of Galaxies in Pairs
- Short Name:
- J/ApJ/511/595
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Results are reported from the first survey of X-ray emission from galaxies in pairs. The sample consists of 52 pairs of galaxies from the Catalog of Paired Galaxies (Cat. <VII/77>) whose coordinates overlap the ROSAT Position Sensitive Proportional Counter pointed observations. The mean observed log(L_x_) for early-type pairs is 41.35+/-0.21, while the mean log(L_x_) predicted using the (L_X_-L_b_) relationship for isolated early-type galaxies is 42.10+/-0.19. With 95% confidence, the galaxies in pairs are underluminous in the X-ray, compared with isolated galaxies, for the same L_b_. A significant fraction of the mixed pair sample also appears similarly underluminous. A spatial analysis shows that the X-ray emission from pairs of both types typically has an extent of 10 - 50 kpc, much smaller than the group intergalactic medium, and thus likely originates from the galaxies. CPG 564, the most X-ray luminous early-type pair, 4.7x10^42^ergs/s, is an exception. The extent of its X-ray emission, greater than 169 kpc, and HWHM, {~}80 kpc, is comparable to that expected from an intergalactic medium. The sample shows only a weak correlation, {~}81% confidence, between L_X_ and L_b_, presumably due to variations in gas content within the galaxies. No correlation between L_X_ and the pair velocity difference ({delta}v), separation ({delta}r), or far-infrared luminosity (L_fir_) is found, although the detection rate is low, 22%.
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- ID:
- ivo://CDS.VizieR/J/ApJS/126/209
- Title:
- Bright SHARC survey cluster catalog
- Short Name:
- J/ApJS/126/209
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the Bright SHARC (Serendipitous High-Redshift Archival ROSAT Cluster) Survey, which is an objective search for serendipitously detected extended X-ray sources in 460 deep ROSAT PSPC pointings. The Bright SHARC Survey covers an area of 178.6 deg^2^ and has yielded 374 extended sources. We discuss the X-ray data reduction, the candidate selection and present results from our on-going optical follow-up campaign. The optical follow-up concentrates on the brightest 94 of the 374 extended sources and is now 97% complete. We have identified 37 clusters of galaxies, for which we present redshifts and luminosities. The clusters span a redshift range of 0.0696<z<0.83 and a luminosity range of 0.065<L_X_< 8.3x10^44^ergs/s [0.5-2.0keV] (assuming H_0_=50km/s/Mpc and q_0_=0.5). Twelve of the clusters have redshifts greater than z=0.3, eight of which are at luminosities brighter than L_X_=3x10^44^ergs/s. Seventeen of the 37 optically confirmed Bright SHARC clusters have not been listed in any previously published catalog. We also report the discovery of three candidate "fossil groups" of the kind proposed by Ponman et al. (1994Natur.369..462P)
- ID:
- ivo://CDS.VizieR/J/ApJ/502/558
- Title:
- Catalog of ROSAT galaxy clusters
- Short Name:
- J/ApJ/502/558
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of 203 clusters of galaxies serendipitously detected in 647 ROSAT PSPC high Galactic latitude pointings covering 158deg^2^. This is one of the largest X-ray-selected cluster samples, comparable in size only to the ROSAT All-Sky Survey sample of nearby clusters (Ebeling et al., 1997ApJ...479L.101E). We detect clusters in the inner 175 of the ROSAT PSPC field of view using the spatial extent of their X-ray emission. Fluxes of detected clusters range from 1.6x10^-14^ to 8x10^-12^ergs/s/cm^2^ in the 0.52keV energy band. X-ray luminosities range from 10^42^ergs/s, corresponding to very poor groups, to ~5x10^44^ergs/s, corresponding to rich clusters. The cluster redshifts range from z=0.015 to z>0.5. The catalog lists X-ray fluxes, core radii, and spectroscopic redshifts for 73 clusters and photometric redshifts for the remainder.
- ID:
- ivo://CDS.VizieR/J/MNRAS/318/333
- Title:
- Extended ROSAT Bright Cluster Sample
- Short Name:
- J/MNRAS/318/333
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a low-flux extension of the X-ray-selected ROSAT Brightest Cluster Sample (BCS) published in Paper I of this series. Like the original BCS and employing an identical selection procedure, the BCS extension is compiled from ROSAT All-Sky Survey (RASS) data in the northern hemisphere ({delta}>=0{deg}) and at high Galactic latitudes (|b|>=20{deg}). It comprises 99 X-ray-selected clusters of galaxies with measured redshifts z<=0.3 (as well as eight more at z>0.3) and total fluxes between 2.8x10^-12^ and 4.4x10^-12^erg/cm^2^/s in the 0.1-2.4keV band (the latter value being the flux limit of the original BCS). The extension can be combined with the main sample published in 1998 to form the homogeneously selected extended BCS (eBCS), the largest and statistically best understood cluster sample to emerge from the RASS to date. The nominal completeness of the combined sample (defined with respect to a power-law fit to the bright end of the BCS logN-logS distribution) is relatively low at 75per cent (compared with 90per cent for the high-flux sample of Paper I). However, just as for the original BCS, this incompleteness can be accurately quantified, and thus statistically corrected for, as a function of X-ray luminosity and redshift. In addition to its importance for improved statistical studies of the properties of clusters in the local Universe, the low-flux extension of the BCS is also intended to serve as a finding list for X-ray-bright clusters in the northern hemisphere which we hope will prove useful in the preparation of cluster observations with the next generation of X-ray telescopes such as Chandra and XMM-Newton.
- ID:
- ivo://CDS.VizieR/J/ApJS/129/435
- Title:
- NORAS galaxy cluster survey. I.
- Short Name:
- J/ApJS/129/435
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the construction of an X-ray-selected sample of galaxy clusters for cosmological studies, we have assembled a sample of 495 X-ray sources found to show extended X-ray emission in the first processing of the ROSAT All-Sky Survey. The sample covers the celestial region with declination {delta}>=0{deg} and Galactic latitude |b|>=20{deg} and comprises sources with a count rate >=0.06counts/s and a source extent likelihood of L>=7. In an optical follow-up identification program we find 378 (76%) of these sources to be clusters of galaxies.
- ID:
- ivo://CDS.VizieR/J/MNRAS/306/857
- Title:
- ROSAT Brightest Cluster Sample. III.
- Short Name:
- J/MNRAS/306/857
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new spectra of dominant galaxies in X-ray-selected clusters of galaxies, which combine with our previously published spectra to form a sample of 256 dominant galaxies in 215 clusters. 177 of the clusters are members of the ROSAT Brightest Cluster Sample (BCS; Ebeling et al., 1998MNRAS.301..881E), and 17 have no previous measured redshift. This is the first paper in a series correlating the properties of brightest cluster galaxies and their host clusters in the radio, optical and X-ray wavebands.
- ID:
- ivo://CDS.VizieR/J/ApJ/519/533
- Title:
- ROSAT observations of ACO clusters
- Short Name:
- J/ApJ/519/533
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have compiled an X-ray catalog of optically selected rich clusters of galaxies observed by the Position Sensitive Proportional Counter (PSPC) during the pointed GO phase of the ROSAT mission. This paper contains a systematic X-ray analysis of 150 clusters with an optical richness classification of R>=2 from the Abell, Corwin, & Olowin (1989; ACO) catalog. All clusters were observed within 45' of the optical axis of the telescope during pointed PSPC observations. For each cluster, we calculate: the net 0.5-2.0keV PSPC count rate (or 4{sigma} upper limit) in a 1Mpc radius aperture, 0.5-2.0keV flux and luminosity, bolometric luminosity, and X-ray centroid. The cluster sample is then used to examine correlations between the X-ray and optical properties of clusters, derive the X-ray luminosity function of clusters with different optical classifications, and obtain a quantitative estimate of contamination (i.e., the fraction of clusters with an optical richness significantly overestimated due to interloping galaxies) in the ACO catalog.
- ID:
- ivo://CDS.VizieR/J/ApJ/514/148
- Title:
- ROSAT survey of bright galaxies clusters
- Short Name:
- J/ApJ/514/148
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe the selection of an X-ray flux-limited sample of bright clusters of galaxies in the southern hemisphere, based on the first analysis of the ROSAT All-Sky Survey data (RASS1). The sample is constructed starting from an identification of candidate clusters in RASS1, after which their X-ray fluxes are remeasured using the steepness-ratio technique. This method is better suited than the RASS1 standard algorithm to measuring flux from extended sources. The final sample is count-rate-limited in the ROSAT hard band (0.5-2.0 keV), so that as a result of the distribution of N_H_, its effective flux limit varies between {~}3 and 4x10^-12^ ergs cm^-2^ s^-1^ over the selected area. This covers the {delta} < 2.5{deg} part of the south Galactic cap region (b < -20{deg}), excluding patches of low RASS1 exposure time and of the Magellanic Clouds area, for a total of 8235 deg^2^. One hundred and thirty candidate sources fulfill our selection criteria for bona fide clusters of galaxies in this area. Of these, 101 are Abell/ACO clusters, while 29 do not have a counterpart in these catalogs. Of these clusters, 126 (97%) have a redshift, and for these we compute an X-ray luminosity. 20% of the cluster redshifts come from new observations, as part of the ESO Key Program survey of RASS clusters that is currently under completion. Considering the intrinsic biases and incompletenesses introduced by the flux selection and source identification processes, we estimate the overall completeness to be better than 90%. The observed number count distribution, log Nlog S, is well fitted by a power law with slope {alpha} =1.34{+/-}0.15 and normalization A=11.87{+/-}1.04 sr^-1^ (10^-11^ ergs cm^-2^ s^-1^)^{alpha}^, in good agreement with other measurements.
- ID:
- ivo://CDS.VizieR/J/MNRAS/301/881
- Title:
- The ROSAT brightest cluster sample - I.
- Short Name:
- J/MNRAS/301/881
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a 90 per cent flux-complete sample of the 201 X-ray-brightest clusters of galaxies in the northern hemisphere ({delta}>=0{deg}), at high Galactic latitudes (|b|>= 20{deg}), with measured redshifts z<=0.3 and fluxes higher than 4.4x10^-12^erg/cm^2^/s in the 0.112.4 keV band. The sample, called the ROSAT Brightest Cluster Sample (BCS), is selected from ROSAT All-Sky Survey data and is the largest X-ray-selected cluster sample compiled to date. In addition to Abell clusters, which form the bulk of the sample, the BCS also contains the X-ray-brightest Zwicky clusters and other clusters selected from their X-ray properties alone. Effort has been made to ensure the highest possible completeness of the sample and the smallest possible contamination by non-cluster X-ray sources. X-ray fluxes are computed using an algorithm tailored for the detection and characterization of X-ray emission from galaxy clusters. These fluxes are accurate to better than 15 per cent (mean 1{sigma} error).
- ID:
- ivo://CDS.VizieR/J/MNRAS/341/1093
- Title:
- The Southern SHARC catalogue
- Short Name:
- J/MNRAS/341/1093
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Southern Serendipitous High-redshift Archival Cluster (SHARC) catalogue is a X-ray selected catalogue of galaxy clusters detected in deep ROSAT observations. The survey area is 17.7deg^2^ and is selected from long (greater than 10ks) ROSAT exposures with a declination <+20deg and excluding the Galactic plane (excluding galactic latitudes within the range [-20,20]deg). Optical follow-up was performed to confirm the presence of a galaxy cluster and measure its redshift. The final catalogue contains 32 galaxy clusters with redshifts between 0.05 and 0.70 and X-ray luminosities between 7x10^35^W and 4x10^37^W. Above a redshift of 0.3 - which forms the primary subsample of the survey - there are 16 clusters; the X-ray luminosities of these clusters are all greater than 2x10^36 W. All X-ray luminosities are quoted in the 0.5-2.0keV band and were calculated using an Einstein-de Sitter cosmology with H_0_ set to 50km/s/Mpc.
