The 2009 Fermi Symposium

The Cosmological Evolution of Blazars and the Extragalactic Gamma-Ray Background in the Fermi Era

Inoue Yoshiyuki, Kyoto University

Abstract:

We present a new model of the blazar gamma-ray luminosity function (GLF) and the spectrum of the extragalactic gamma-ray background (EGRB), which is consistent with the observed distributions of EGRET (Energetic Gamma-Ray Experiment Telescope) blazars. The unified sequence of blazar spectral energy distribution is taken into account to make a nontrivial prediction for the EGRB spectrum and more realistic comparison with the data than previous studies. We then try to explain the EGRB data by the two AGN populations: one is blazars, and the other is nonblazar AGNs that are responsible for the EGRB in the MeV band. We find that ∼80% of the EGRB photon flux at >100 MeV can be explained by the sum of the two populations, while ∼45% can be accounted for only by blazars. The predicted EGRB spectrum is in agreement with a wide range of the observed data from X-ray to GeV including the very recent EGRB data by the Fermi Gamma-ray Space Telescope. These results i! ndicate that AGNs including blazars are the primary source of EGRB. Almost all of the EGRB flux from blazars will be resolved into discrete sources by Fermi, while that from non-blazar AGNs will largely remain unresolved. Our model predicts ∼750 blazars in all sky down to one year Fermi sensitivity. Although the high-redshift evolution of our GLF is uncertain, by scaling with the observed evolution of SDSS quasars up to z∼5, we also show that Fermi may be able to find blazars up to z∼7. Such high-redshift blazars would provide a new probe of the UV background from early stars through the resulting attenuation features in their GeV spectra.