Deep survey sources, and predictions for XMM and AXAF Original Research Article

From the deep surveys performed with the ROSAT and ASCA X-ray observatories, we have now built up a plausible picture of the constitution of the X-ray background and the way in which AGNs (and starburst nuclei surrounding AGNs) account for it. But major problems remain: the best model that we have is one in which the XRB above 3 kev is accounted for by AGN with large and unknown NH columns, i.e. the distribution of unknown NH values is critical to this hypothesis. With reasonable assumptions, however, we can make predictions for the source populations that we should detect in the AXAF and XMM deep surveys. In this paper, we compare the expected number counts from the two observatories, and comment on the quality of the X-ray spectra from each.The results of ROSAT deep surveys were well established during the first few years of ROSAT operation (see references to the ROSAT/ASCA collaboration). They have allowed us to measure the AGN Luminosity Function and its evolution in soft X-rays, both for AGN of Type I and for objects classified as AGN Type II/Narrow-Line X-ray Galaxy (NLXG). Deep surveys have been performed with ASCA of some of these same ROSAT fields. Significant cosmological evolution has been observed for Type I AGN in the 2–10 keV energy range, with an evolutionary rate which is consistent with that measured in other passbands. The predicted contribution of Type I AGN to the 2–10 keV X-ray background (XRB) is nearly 40% when extrapolated to AXAF deep survey flux limits, and the corresponding combined contribution from AGN of Types I & II is about 65%.