The Chandra Deep Field South: Preliminary x-ray and optical results

We present first results of the survey of the Chandra Deep Field South from 130 ks of x-ray observations in the .5 - 10 kev range obtained with the Advanced CCD Imaging Spectrometer in the Chandra X-ray Observatory. We observe a total of 160 sources to limiting fluxes of 2x10(-16) ergs(-1) cm(-2) in the .5 - 2 kev soft band and 2 x 10(-15)ergs(-1) cm(-2) in the 2 - 10 kev hard band. We discuss the spectra of the x-ray sources, the Log N-Log S relationship and the discrete source contribution to the integrated sky flux in the two bands. For purposes of identification of the optical counterparts we use observations obtained at the VLT with FORS-1 in the VRI bands complete to R less than or equal to 26 in a large fraction of the x-ray field, supplemented with data from the ESO Imaging Survey (EIS) in the UBJK bands and the ESO Wide Field Imager Survey (WFI) in the B band. Positional accuracy of about 1" is obtained for the x-ray sources and about 90% of them can be readily identified with optical candidate objects. Optical spectra have been obtained for 12 sources. Among the outstanding early results are the resolution of the XRB in the 2 - 10 kev range into discrete sources at a level of 60 to 80% of the total; the determination of the hardening of the x-ray spectra of sources at low fluxes which makes them consistent with that of the XRB, and the detection of low x-ray luminosity galaxies in the soft band at Z similar to 2.