Resolving The X–ray Background With Chandra: The 1MS Observation Of The Chandra Deep Field South

The Chandra X–ray Observatory completed a 940 ksec exposure with ACIS–I of the Chandra Deep Field South (herafter CDFS) on December 24, 2000. We review here the main findings from the X-ray analysis of this dataset. We detected 360 sources, mostly AGNs, down to limiting fluxes of $5 × 10^{−17}$ erg $cm^{−2} s^{−1}$ in the soft $0.5^{–2}$ keV band and $4 × 10^{−16}$ erg $cm^{−2} s^{−1}$ in the hard 2–10 keV band on a 0.1089 square degrees field. The LogN–LogS relations show the resolution of the X–ray background into point sources at the level of 83–99% in the 1–2 keV band and 65–98% in the hard 2–10 keV band, given the uncertainties in the unresolved value. The so called “spectral paradox” is solved by a hard, faint population of sources constituted mostly by nearby (z ≤ 1) absorbed (Type II) AGNs with luminosities $L\simeq 10^{42} − 10^{44}$ erg $s^{−1}$. We discuss also other populations of X–ray sources detected in the CDFS, namely soft, low–luminosity normal galaxies, and some relevant extended sources.