The Fermi-LAT GeV Excess Traces Stellar Mass in the Galactic Bulge

TL;DR

This study reanalyzed the Fermi-LAT GeV excess using a novel method and found that its spatial distribution closely follows stellar mass in the Galactic bulge, suggesting a stellar origin rather than dark matter.

Contribution

The paper introduces SkyFACT, a new combined image reconstruction and template fitting tool, to analyze the GeV excess and demonstrates its stellar mass correlation with high significance.

Findings

The excess emission correlates strongly with stellar mass in the bulge.

Stellar mass templates outperform dark matter profiles statistically.

Luminosity to stellar mass ratios are quantified for bulge components.

Abstract

An anomalous emission component at energies of a few GeV and located towards the inner Galaxy is present in the Fermi-LAT data. It is known as the Fermi-LAT GeV excess. Using almost 8 years of data we reanalyze the characteristics of this excess with SkyFACT, a novel tool that combines image reconstruction with template fitting techniques. We find that an emission profile that traces stellar mass in the boxy and nuclear bulge provides the best description of the excess emission, providing strong circumstantial evidence that the excess is due to a stellar source population in the Galactic bulge. We find a luminosity to stellar mass ratio of $(2.1\pm 0.2)\times 10^{27} \mathrm{\,erg\,s^{-1}\,M_\odot^{-1}}$ for the boxy bulge, and of $(1.4\pm 0.6)\times 10^{27}\mathrm{\,erg\,s^{-1}\,M_\odot^{-1}}$ for the nuclear bulge. Stellar mass related templates are preferred over conventional DM profiles with high statistical significance.