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

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.

arXiv comment21 pages, 7 figures, V2: Minor modifications, main conclusions unchanged. V3: version submitted to Nature Astronomy. V4: matches Nature Astronomy published version. The hydrodynamical interstellar maps used in this work are available at https://github.com/chrisgordon1/galactic_bulge

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