THE COSMOLOGICAL EVOLUTION MODELS OF ACTIVE GALAXIES AND THE EXTRAGALACTIC GAMMA-RAY BACKGROUND

One theory for the origin of the extragalactic γ-ray background radiation (EGB) is that it is made up of the superposed fluxes of many sources, the sources being active galactic nuclei (AGNs). In this Letter, we investigate the source spectra and angular fluctuations produced by various possible models of AGN evolution derived from observations in other wavelength bands. We find that the sizes of the angular fluctuations are roughly constant between 10 and 100 MeV, independent of the models chosen. None of our models produce the spectral "shelf" observed at a few MeV, and from our simulation, the AGN mechanism is only a minor contributor to the EGB, with its flux only ∼10% of what is observed. These evolution-independent effects imply that the EGB is not solely produced by the AGN mechanism. Thus, more than one type of underlying generation mechanism for the EGB appears to be called for.