Realistic estimation for the detectability of dark matter subhalos using Fermi-LAT catalogs

Numerical simulations of structure formation have made remarkable progress in recent years, in particular due to the inclusion of baryonic physics evolving with the dark matter component. We generate Monte Carlo realizations of the dark matter subhalo population based on the results of the recent hydrodynamical simulation suite of Milky Way–sized galaxies [F. Marinacci, R. Pakmor, and V. Springel, Mon. Not. R. Astron. Soc. 437, 1750 (2014).]. We then simulate the gamma-ray sky for both the setup of the 3FGL and 2FHL Fermi Large Area Telescope (LAT) catalogs, including the contribution from the annihilation of dark matter in the subhalos. We find that the flux sensitivity threshold strongly depends on the particle dark matter mass and, more mildly, also on its annihilation channel and the observation latitude. The results differ for the 3FGL and 2FHL catalogs, given their different energy thresholds. We also predict that the number of dark matter subhalos among the unassociated sources is very small. A null number of detectable subhalos in the Fermi-LAT 3FGL catalog would imply upper limits on the dark matter annihilation cross section into bb¯ of 2×10−26(5×10−25) cm3/s with MDM=50(1000) GeV. We find less than one extended subhalo in the Fermi-LAT 3FGL catalog. As a matter of fact, the differences in the spatial and mass distribution of subhalos between hydrodynamic and dark matter–only runs do not have significant impact on the detectability of dark subhalos in gamma rays.