Can AGN alone make the cosmic X‐ray background?

Recent ROSAT X‐ray observations of AGN have yielded important new information about the analytic structure of the AGN X‐ray luminosity function and its evolution to redshift z=3 (Boyle et al. 1993). Using the luminosity evolution obtained within the cosmological context of Ω=0 we find, as recently noted by Zdziarski, Zycki, & Krolik (1993), that AGN could readily make up the CXB (cosmic X‐ray background). However, in this case we conclude that accounting for the CXB with accretion‐powered AGN emission is incompatible with the observed mass function for present‐epoch black hole galactic nuclei (both active and dormant). Although the luminosity evolution obtained with ROSAT for Ω=1 is indeed compatible with this mass function such a scenario definitely falls short of accounting for all the CXB, even when considering unified AGN models. We suggest that in this case the X‐radiation characteristic of highly compact PAG (precursor active galaxies) sources indicative of the initial black hole mass growth desired...