Gamma ray and Neutrino fluxes from a cosmological dark matter simulation

Abstract

In this paper, we estimate the gamma-ray and neutrino fluxes coming from dark matter annihilation in a Milky Way framework provided by a recent N-BODY HORIZON simulation. We first study the characteristics of the simulation and highlight the mass distribution within the galactic halo. The general dark matter density has a typical $r^{-3}$ power law for large radii, but the inner behaviour is poorly constrained below the resolution of the simulation ($\sim 200$ pc). We identify clumps and subclumps and analyze their distribution, as well as their internal structure. Inside the clumps, the power law is rather universal, $r^{-2.5}$ in the outer part with again strong uncertainties for smaller radii, especially for light clumps. We show a full-sky map of the astrophysical contribution to the gamma-ray or neutrino fluxes in this N-body framework. Using quite model independent and general assumptions for the high energy physics part, we evaluate the possible absolute fluxes and show some benchmark regions for the experiments GLAST, EGRET, and a km3 size extension of ANTARES like the KM3NeT project. While individual clumps seem to be beyond detection reach, the galactic center region is promising and GLAST could be sensitive to the geometry and the structure of its dark matter distribution. The detection by a km3 version of ANTARES is, however, more challenging due to a higher energy threshold. We also point out that the lack of resolution leaves the inner structure of subhalos poorly constrained. Using the same clump spectrum and mass fraction, a clump luminosity boost of order ten can be achieved with a steeper profile in the inner part of the sub-halos.