The Chandra Deep Field–South: Optical Spectroscopy. I.

We present the results of our spectroscopic follow-up program of the X-raysources detected in the 942 ks exposure of the Chandra Deep Field South (CDFS).288 possible counterparts were observed at the VLT with the FORS1/FORS2spectrographs for 251 of the 349 Chandra sources (including three additionalfaint X-ray sources). Spectra and R-band images are shown for all the observedsources and R-K colours are given for most of them. Spectroscopic redshiftswere obtained for 168 X-ray sources, of which 137 have both reliable opticalidentification and redshift estimate (including 16 external identifications).The R<24 observed sample comprises 161 X-ray objects (181 optical counterparts)and 126 of them have unambiguous spectroscopic identification. We introduce anew classification based solely on X-ray properties, HR and X-ray luminosity,consistent with the unified AGN model. This X-ray classification uncovers alarge fraction of optically obscured, X-ray luminous AGNs missed by theclassical optical classification.