Münster 2017 – scientific programme

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T: Fachverband Teilchenphysik

T 106: Suche nach Dunkler Materie 4

T 106.1: Group Report

Thursday, March 30, 2017, 16:45–17:05, VSH 19

Why the Fermi GeV gamma-ray excess cannot be explained by dark matter annihilation — •Wim de Boer, Iris Gebauer, Alexander Neumann, and Peter L. Biermann — Karlsruhe Institut of Technology (KIT), Karlsruhe, Germany

The "GeV-excess" of the diffuse gamma-rays in the halo is studied with a template fit based on energy spectra for each possible process of gamma-ray emission. Such a fit allows to determine the background and signal simultaneously, leading to a reliable background determination even in the Galactic Disk, largely independent of propagation models or gas distributions. We find evidence that the "excess", characterised by a gamma-ray spectrum peaking at 2 GeV, is related to the propagation inside Molecular Clouds (MCs), which show this excess, as is apparent from the Central Molecular Zone.

We find that the "excess" has the same morphology as the column density of MCs, as was apparent from the comparison with the CO maps from the Planck satellite. These CO maps are tracers from MCs and happen to lead to an emissivity resembling a typical dark matter proflle. However, outside the Galactic Bar the Molecular Clouds and the observed "excess" in the Galactic Disk abruptly show a decrease, so the excess cannot originate from a process surrounding spherically the Galactic Center.