The signature of large scale structures on the very high energy gamma ray sky

If the diffuse extragalactic gamma ray emission traces the large scale structures of the universe, peculiar anisotropy patterns are expected in the gamma ray sky. In particular, because of the cut-off distance introduced by the absorption of 0.1–10 TeV photons on the infrared/optical background, prominent correlations with the local structures within a range of few hundreds of Mpc should be present. We provide detailed predictions of the signal based on the PSCz map of the local universe. We also use mock N-body catalogues complemented with the halo model of structures to study some statistical features of the expected signatures. The results are largely independent of cosmological details, and depend mostly on the index of correlation (or bias) of the sources with respect to the large scale distribution of galaxies. For instance, the predicted signal in the case of a quadratic correlation (as may happen for a dark matter annihilation contribution to the diffuse gamma flux) differs substantially from a linear correlation case, providing a complementary tool for unveiling the nature of the sources of the diffuse gamma ray emission. The chances for the present and future space and ground based observatories to measure these features are discussed.