Overdensity of X-ray sources in the field of two nearby clusters of galaxies: XMM-Newton view of A 194 and A 1060

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Hudaverdi M., Kunieda H., Tanaka T., Haba Y., Furuzawa A., TAWARA Y., ...More

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN, vol.58, no.6, pp.931-943, 2006 (SCI-Expanded) identifier identifier


Two nearby Clusters of galaxies, A 194 (z = 0.018) and A 1060 (z = 0.0114), have been analyzed for their X-ray point-source properties with XMM-Newton EPIC-PN data. A multi-band source detection technique was applied to both of the clusters, resulting in 46 sources from the A 194 field and 32 sources from the A 1060 field, respectively. The cumulative log(N)-log(S) for a flux limit of F-X >= I X 10(-14) erg cm(-2)s(-1) was calculated and compared with that of the Lockman Hole. A similar to 3 sigma excess of X-ray sources was found for the cluster regions. Considering the higher fraction observed in optical studies from the clusters, we estimate that the cluster source density is 6-times higher than the blank-field source density, and 15-firries higher than the local group. Our X-ray selected sources have luminosity values of 10(39.6) <= Lx <= 10(41.4) erg s(-1), in which X-ray emission from LMXBs, hot halos and starburst galaxies becomes noticeable. The significance of the source-density excess gradually vanishes for sources with L-X >= 10(40.5) erg s(-1), at which point the source density becomes comparable to that of the blank-field level. Considering this confined low-luminosity range and the X-ray to optical luminosity ratios (L-X/L-B), the observed overdensity is ascribed to AGN fueling by its infall into cluster environment for L-X <= 10(40.5) erg s(-1) in the X-ray luminosity function. However, the quenching of AGN activity by the deep Cluster potential explains why the excess of the source density vanishes for brighter sources.