HST Imaging in the Chandra Deep Field South: I. Multiple AGN Populations

E. J. Schreier, A. M. Koekemoer, N. A. Grogin, R. Giacconi, R. Gilli, L. Kewley, C. Norman, G. Hasinger, P. Rosati, A. Marconi, M. Salvati, P. Tozzi

Published 2001-05-16Version 1

We present preliminary results from imaging three HST/WFPC2 fields in V and I within the Chandra Deep Field South (CDFS). HST's sensitivity and resolution are sufficient to reveal optical counterparts for 24 of the 26 CDFS X-ray sources detected in the 300 ksec X-ray catalog and to determine the morphologies of most of these. We find that the X-ray sources comprise two apparently distinct populations of optical candidates: one optically faint (I > 24) with V - I colors consistent with the I > 24 field population; the other significantly brighter (I < 22) with colors redder than the I < 22 field population. More than 2/3 of the X-ray source counterparts are resolved galaxies. The brighter sources are mostly AGN, based on their high X-ray luminosity. The optically resolved sources in the brighter population have a very narrow range of V - I color and appear to be a mix of both late and early type morphologies at low to moderate redshift. We show that the second population, with fainter optical counterparts, can be explained as higher redshift Type 2 AGN.