Chandra COSMOS (C-COSMOS) Survey Optical/IR Counterparts Catalog

The Chandra COSMOS Survey (C-COSMOS) is a large, 1.8-Ms, Chandra program that has imaged the central 0.9 deg² of the COSMOS field down to limiting depths of 1.9 x 10^-16 erg/cm²/s in the soft (0.5-2 keV) band, 7.3 x 10^-16 erg/cm²/s in the hard (2-10 keV) band, and 5.7 x 10^-16 erg/cm²/s in the full (0.5-10 keV) band. In this Paper III of the series of papers on this survey, the authors report the i, K, and 3.6-um identifications of the 1761 X-ray point sources.

They use the likelihood ratio technique to derive the association of optical/infrared counterparts for 97% of the X-ray sources. For most of the remaining 3%, the presence of multiple counterparts or the faintness of the possible counterpart prevented a unique association. For only 10 X-ray sources, they were not able to associate a counterpart, mostly due to the presence of a very bright field source close by.