Discovery of Gamma-Ray Emission from the X-shaped Bulge of the Milky Way

Oscar Macias, Chris Gordon, Roland M. Crocker, Brendan Coleman, Dylan Paterson, Shunsaku Horiuchi, Martin Pohl

Published 2016-11-21Version 1

An anomalous signal has been found in Fermi Gamma-Ray Large Area Telescope data covering the center of the Galaxy. Given its morphological and spectral characteristics, this "Galactic Center Excess" is ascribable to self-annihilation of dark matter particles. We report on an analysis that exploits hydrodynamical modeling to register the position of interstellar gas associated with diffuse Galactic $\gamma$-ray emission. Our improved analysis reveals that the excess $\gamma$-rays are spatially correlated with both the X-shaped stellar over-density in the Galactic bulge and the nuclear stellar bulge. Given these correlations, we argue that the excess is not a dark matter phenomenon but rather associated with the stellar population of the X-bulge and the nuclear bulge.