Dark matter annihilation and the Galactic Centre Excess

TL;DR

This study compares gamma-ray observations of the Galactic Centre Excess with dark matter annihilation models from high-resolution galaxy simulations, supporting dark matter as the likely source of the excess.

Contribution

It demonstrates that galaxy simulations including baryonic effects match the observed gamma-ray profile, strengthening the dark matter annihilation hypothesis for the GCE.

Findings

Simulations with baryons reproduce the GCE's central concentration.

Dark-matter only simulations fail to match the observed profile.

Results set upper limits on dark matter annihilation rates.

Abstract

We compare the surface brightness profile and morphology of the Galactic Centre Excess (GCE) identified in wide-angle $\gamma$-ray maps from the Fermi-Large Area Telescope to dark matter annihilation predictions derived from high-resolution $\Lambda$CDM magnetohydrodynamic simulations of galaxy formation. These simulations produce isolated, disc-dominated galaxies with structure, stellar populations, gas content, and stellar and halo masses comparable to those of the Milky Way. For a specific choice of annihilation cross-section, they agree well with the Fermi-LAT data over the full observed angular range, $1^{\circ}$ to $15^{\circ}$, whereas their dark-matter only counterparts, lacking any compression of the inner halo by the gravitational effects of the baryons, fail to predict emission as centrally concentrated as observed. These results provide additional support to the hypothesis that the GCE is produced by annihilating dark matter. If, however, it is produced by a different mechanism, they imply a strong upper limit on annihilation rates which can be translated into upper limits on the expected $\gamma$-ray flux not only from the inner Galaxy but also from any substructure, with or without stars, in the Galactic halo.