Evaluation of the contribution of different types of galaxies to the cosmic diffuse background based on gamma-ray observations

The relative contribution to the gamma-ray background of different types of sources, namely Seyfert galaxies, quasars, BL Lac objects, radio galaxies, and field galaxies is estimated under the hypothesis that the cosmic diffuse flux is the result of a superposition of many unresolved galaxies. The gamma-ray data indicate that the Seyfert volume emissivity matches that of the diffuse background at few hundred keV and exceeds it at higher energies by as much as a factor of about four. While normal galaxies contribute less than 0.1 percent, BL Lac objects, quasars and radio galaxies may contribute as much as 5-10 percent each, even without significant evolution. In this paper, different ways of reconciling the observational data on active galaxies with the measured diffuse background level are explored. 17 references