Galactic Bulge Preferred Over Dark Matter for the Galactic Center Gamma-Ray Excess

TL;DR

This study suggests that the gamma-ray excess observed in the Galactic Center is more likely due to stellar populations in the bulge rather than dark matter annihilation, based on hydrodynamical modeling of interstellar gas.

Contribution

The paper introduces a hydrodynamical modeling approach to better associate gamma-ray excess with stellar populations instead of dark matter in the Galactic Center.

Findings

Gamma-ray excess correlates with stellar over-density in the bulge.

The excess is better explained by stellar populations than dark matter.

The excess's non-spherical shape argues against a dark matter origin.

Abstract

An anomalous gamma-ray excess emission has been found in Fermi Large Area Telescope data covering the centre of the Galaxy. Several theories have been proposed for this `Galactic Centre Excess'. They include self-annihilation of dark matter particles, an unresolved population of millisecond pulsars, an unresolved population of young pulsars, or a series of burst events. Here we report on a new analysis that exploits hydrodynamical modelling to register the position of interstellar gas associated with diffuse Galactic gamma-ray emission. We find evidence that the Galactic Centre Excess gamma rays are statistically better described by the stellar over-density in the Galactic bulge and the nuclear stellar bulge, rather than a spherical excess. Given its non-spherical nature, we argue that the Galactic Centre Excess is not a dark matter phenomenon but rather associated with the stellar population of the Galactic bulge and nuclear bulge.