Realistic estimation for the detectability of dark matter sub-halos with Fermi-LAT

TL;DR

This paper models the gamma-ray detectability of dark matter sub-halos with Fermi-LAT, considering recent hydrodynamical simulations, and predicts the number of observable sub-halos and constraints on dark matter properties.

Contribution

It introduces a realistic estimation method for dark matter sub-halo detectability using updated hydrodynamical simulation data and gamma-ray sky simulations for Fermi-LAT catalogs.

Findings

The flux sensitivity depends on dark matter mass and annihilation channel.

The expected number of detectable sub-halos is very small.

Null detection implies upper limits on the dark matter annihilation cross section.

Abstract

Numerical simulations of structure formation have recorded a remarkable progress in the 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 sub-halo population based on the results of the recent hydrodynamical simulation suite of Milky Way-sized galaxies. 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 sub-halos. 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 sub-halos among the unassociated sources is very small. A null number of detectable sub-halos in the Fermi-LAT 3FGL catalog would imply upper limits on the dark matter annihilation cross section into $b\bar{b}$ of $2 \cdot 10^{-26}$ ($5 \cdot 10^{-25}$) cm$^3$/s with $M_{\rm DM}$= 50 (1000) GeV. We find less than one extended sub-halo in the Fermi-LAT 3FGL catalog. As a matter of fact, the differences in the spatial and mass distribution of sub-halos between hydrodynamic and dark matter-only runs do not have significant impact on the gamma-ray dark matter phenomenology.