The Host Galaxies and Environment of Chandra-Selected Active Galactic Nuclei in the Deep ACS GTO Cluster Fields

We present catalogs and images of optical counterparts to the Chandra-selected X-ray sources found in the fields of the five clusters RX J0152-1357, RX J0849+4452, RDCS J0910+5422, MS 1054-0321, and RDCS J1252-2927, which were imaged with the Advanced Camera for Surveys as part of the ACS Guaranteed Time Observer programs. A total of 98 X-ray sources fall within the ACS mosaics, and positive identifications are made for ~96% of them, including confirmed cluster members. We classify the sources as active galactic nuclei (AGNs) or QSOs depending on their X-ray output. The logN(>S)-logS test indicates a significant overdensity of X-ray sources in the RX J0152-1357, RDCS J0910+5422, and MS 1054-0321 fields with respect to the CDF-S, suggesting an association of some X-ray sources with the large-scale structure of the clusters. From the asymmetry and concentration indices, ~52% of the optical counterparts are early-type galaxies, ~35% late-type, and the remainder irregular. A blue core is found in approximately half of the early-type galaxies. From visual examination, approximately 40% of the counterparts possess an unresolved nucleus, a common signature of nuclear activity. A majority of these nuclei are found in near face-on late-type galaxies although selection effects might be important. The X-ray to optical flux ratio of the nuclei correlates with the inclination angle of the late-type galaxies but not of the early types, as expected if dust is significant in the circumnuclear regions. The AGNs possess a ~50% excess of nearby companions compared to the overall galaxy population in the same fields. The surface density of the X-ray sources is highest at projected radii of <~1 Mpc from the cluster center and relatively flat at larger radii. We describe the morphology and environment of the cluster members and compare them with the other optical counterparts.

Based on observations made with the NASA/ESA Hubble Space Telescope, which is operated by AURA, Inc., under NASA contract NAS 5-26555.