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Description
This table contains the Swift X-ray Cluster Survey (SWXCS) table of cross-correlations of the X-ray galaxy cluster and group candidates with optical, X-ray and Sunyaev-Zel'dovich catalogs and optical follow-up. The SWXCS list of cluster candidates was obtained using archival data from the X-ray telescope (XRT) on board the Swift satellite acquired from 2005 February to 2012 November, extending the first release of the SWXCS. The main catalog (available at the HEASARC as the linked table SWXCSCAT) provides positions and soft X-ray fluxes for a flux-limited sample of X-ray group and cluster candidates. The table herein (based on Table 3 of the reference paper) contains when possible, optical and other counterparts for these candidates. The authors consider the fields with Galactic latitude |b| > 20 degrees so as to avoid regions of high H I column density. They discard all of the observations targeted at groups or clusters of galaxies, as well as particular extragalactic fields not suitable for searching for faint extended sources. The authors finally select ~ 3000 useful fields covering a total solid angle of ~ 400 deg<sup>2</sup>. They identify extended source candidates in the soft-band (0.5-2 keV) images of these fields using the software EXSdetect, which is specifically calibrated for the XRT data. Extensive simulations are used to evaluate contamination and completeness as a function of the source signal, allowing the authors to minimize the number of spurious detections and to robustly assess the selection function. The final catalog includes 263 candidate galaxy clusters and groups down to a flux limit of 7 x 10<sup>-15</sup> erg/cm<sup>2</sup>/s in the soft band (0.5 - 2.0 keV), and the log N - log S is in very good agreement with previous deep X-ray surveys. In the reference paper, the final list of sources is cross-correlated with published optical, X-ray, and Sunyaev-Zel'dovich catalogs of clusters. The authors find that 137 sources have been previously identified as clusters in the literature in independent surveys, while 126 are new detections. Currently, they have collected redshift information for 158 sources (60% of the entire sample). The authors checked for counterparts in previous X-ray cluster surveys, in optical cluster surveys, and in the Planck SZ cluster survey. They simply assume a search radius of 2 arcminutes from the X-ray centroid, which has been shown to be an efficient criterion in Paper I. Nevertheless, they also inspected the area within 5 arcminutes from the X-ray centroid in order to investigate whether some possible identification is found at radii larger than 2 arcminutes. Counterparts at distances between 2 and 5 arcminutes are included when the optical or SZ corresponding source has a large uncertainty in its position. This is often the case for optical, sparse clusters, or for SZ cluster candidates. The authors list all of the counterparts associated with the SWXCS sources herein, and they include the measured redshift when available. In case of multiple counterparts, they list all of them. Except for a few cases where there are multiple counterparts with statistically inconsistent redshifts, the authors keep the counterpart with the smallest angular distance from the X-ray center. From optical surveys, the authors found 233 optical counterparts corresponding to 116 SWXCS sources. From X-ray surveys, they found 70 X-ray counterparts classified as clusters, corresponding to 36 SWXCS sources. Finally, for 15 SWXCS sources, they found 16 cluster counterparts detected via the SZ effect, 13 by Planck and 3 by the South Pole Telescope (SPT). The Planck sources are typically at larger distances from the X-ray centroid (between 1 and 3 arcminutes) because of the much larger position errors of Planck clusters. Overall, about half (137) of the 263 SWXCS sources were previously identified as groups or clusters of galaxies, while 126 SWXCS sources are new cluster and group candidates. The authors have collected spectroscopic or photometric redshifts for 130 of their sources. Moreover, to increase the number of available redshifts, they also searched in NED catalogs for single galaxies with published redshifts not associated with previously known clusters within a search radius of 7 arcseconds from the X-ray centroid of their sources. They find 50 galaxies with measured redshifts for 47 of their sources as a complement to the redshifts obtained from cluster counterparts. In 35 cases where the authors have both cluster and galaxy counterparts, the galaxy redshifts are consistent with those of clusters. In the 12 cases where no cluster counterpart is found, the authors tentatively assign the galaxy redshift to their X-ray source. This table was created by the HEASARC in March 2015 based on an electronic version of Table 3 from the reference paper which was obtained from the CDS as their catalog J/ApJS/216/28 file table3.dat. This is a service provided by NASA HEASARC .
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