Scrutinizing the Gamma-Ray Background in Search of Dark Matter

Several classes of astrophysical sources contribute to the approximately isotropic gamma-ray background measured by the Fermi Gamma-Ray Space Telescope. Using Fermi's catalog of gamma-ray sources (along with corresponding source catalogs at infrared and radio wavelengths) we build and constrain a model for the contributions to the extragalactic gamma-ray background from astrophysical sources, including radio galaxies, star-forming galaxies, and blazars. We then combine our model with Fermi's measurement of the gamma-ray background to derive constraints on the dark matter annihilation cross section, including contributions from both extragalactic and galactic halos and subhalos. The resulting constraints are competitive with the strongest current constraints from the dwarf spheroidal galaxies. Infact, we find an indication for a small flux excess in the extragalactic background consistent with the gamma-ray excess toward the galactic center.