Angular power spectrum of gamma-ray sources for GLAST:: blazars and clusters of galaxies

Blazars, a beamed population of active galactic nuclei, radiate high-energy gamma-rays, and thus are a good target for the Gamma Ray Large Area Space Telescope (GLAST). As the blazars trace the large-scale structure of the Universe, one may observe spatial clustering of blazars. We calculate the angular power spectrum of blazars that would be detected by GLAST. We show that we have the best chance of detecting their clustering at large angular scales, theta greater than or similar to 10 degrees, where shot noise is less important, and the dominant contribution to the correlation comes from relatively low redshift, z less than or similar to 0.1 . The GLAST can detect the correlation signal, if the blazars detected by GLAST trace the distribution of low-z quasars observed by optical galaxy surveys, which have the bias of unity. If the bias of blazars is greater than 1.5, GLAST will detect the correlation signal unambiguously. We also find that GLAST may detect spatial clustering of clusters of galaxies in gamma-rays. The shape of the angular power spectrum is different for blazars and clusters of galaxies; thus, we can separate these two contributions on the basis of the shape of the power spectrum.