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R. Giacconi (AUI/JHU), P. Rosati (ESO), P. Tozzi, S. Borgani (Trieste Obs.), G. Hasinger (AIP), J. Bergeron, R. Gilmozzi (ESO), M. Nonino (Trieste Obs.), R. Gilli (Arcetri), A. Zirm, J.X. Wang, W. Zheng (JHU), K.I. Kellermann (NRAO), P. Shaver (ESO), E. Schreier, A. Koekemoer, N. Grogin (STScI), C. Norman (JHU/STScI)
We present results from the on-going ultra deep Chandra observations in the Chandra Deep Field South (CDF-S). As of October 2000, we have collected an exposure of 300 ksec which covers an area of 0.1 deg2. These new data confirm and strengthen some of the conclusions of our initial analysis based on 130ksec observations (Giacconi et al. 2000). At the current depth, the source surface density is ~3000/deg2. Number counts in the hard band (2-10keV) have overtaken the soft (0.5-2) counts and show evidence of flattening below 10-15 erg/cm2/s [2-10 keV]. The hardening of the source spectra continues to fainter fluxes, most likely the result of an increasing absorption column. We discuss the implications of these observations in light of new population synthesis models. We will also show the spectro-photometric and morphological properties of the optical counterparts from the on-going source identification program with the VLT and HST/WFPC2. We acknowledge support from NASA grants NAG-8-1527 and NAG-8-1133.