Microfiche. Although It Is Recognized That Certain Portions Are Illegible, It Is Being Released in the Interest of Making Available as Much Information as Possible

It is argued that the cosmic X-ray background (CXB) is not dominated by sources that are usual active galaxies or quasars. A comparable number of objects, young galaxies at z < 4 containing massive black holes surrounded by hot optically thin accretion disks, constitute the precursor active galaxies (PAG) postulated here for producing the thermal type spectrum required for the CXB. An evolutionary track for such PAG objects is described which would lead to the active galaxies observed as individual non-thermal sources. Unresolved emission from active galaxies at z < 1 could then readily account for most of the non-thermal background observed in the gamma-ray band. 1NAS-NRC Research Associate