- 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/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/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).
