Chandra Deep Field South: The 1 Ms Catalog

We present the main results from our 940 ksec observation of the Chandra DeepField South (CDFS), using the source catalog described in an accompanying paper(Giacconi et al. 2001). We extend the measurement of source number counts to5.5e-17 erg/cm^2/s in the soft 0.5-2 keV band and 4.5e-16 erg/cm^2/s in thehard 2-10 keV band. The hard band LogN-LogS shows a significant flattening(slope~=0.6) below ~1e-14 erg/cm^2/s, leaving at most 10-15% of the X-raybackground (XRB) to be resolved, the main uncertainty lying in the measurementof the total flux of the XRB. On the other hand, the analysis in the very hard5-10 keV band reveals a relatively steep LogN-LogS (slope ~=1.3) down to 1e-15erg/cm^2/s. Together with the evidence of a progressive flattening of theaverage X-ray spectrum near the flux limit, this indicates that there is stilla non negligible population of faint hard sources to be discovered at energiesnot well probed by Chandra, which possibly contribute to the 30 keV bump in thespectrum of the XRB. We use optical redshifts and identifications, obtainedwith the VLT, for one quarter of the sample to characterize the combinedoptical and X-ray properties of the CDFS sample. Different source types arewell separated in a parameter space which includes X-ray luminosity, hardnessratio and R-K color. Type II objects, while redder on average than the fieldpopulation, have colors which are consistent with being hosted by a range ofgalaxy types. Type II AGN are mostly found at z<~1, in contrast withpredictions based on AGN population synthesis models, thus suggesting arevision of their evolutionary parameters.Comment: Accepted by The Astrophysical Journal, 24 pages, 8 figures, 1 color jpg plate (fig.1