2007ApJS..168...19M

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.