What the Milky Way’s dwarfs tell us about the Galactic Center extended gamma-ray excess

Abstract

The Milky Way's Galactic Center harbors a gamma-ray excess that is a candidate signal of annihilating dark matter. Dwarf galaxies remain predominantly dark in their expected commensurate emission. In this work we quantify the degree of consistency between these two observations through a joint likelihood analysis. In doing so we incorporate Milky Way dark matter halo profile uncertainties, as well as an accounting of diffuse gamma-ray emission uncertainties in dark matter annihilation models for the Galactic Center extended gamma-ray excess (GCE) detected by the Fermi Gamma-Ray Space Telescope. The preferred range of annihilation rates and masses expands when including these unknowns. Even so, using two recent determinations of the Milky Way halo's local density leaves the GCE preferred region of singlechannel dark matter annihilation models to be in strong tension with annihilation searches in combined dwarf galaxy analyses. A third, higher Milky Way density determination, alleviates this tension. Our joint likelihood analysis allows us to quantify this inconsistency. We provide a set of tools for testing dark matter annihilation models' consistency within this combined data set. As an example, we test a representative inverse Compton sourced self-interacting dark matter model, which is consistent with both the GCE and dwarfs.

Foreground mismodeling and the point source explanation of the Fermi Galactic Center excess

“…where the scale radius is r s ¼ 20 kpc. The canonical NFW profile has γ ¼ 1, but motivated by previous studies [9,13,54], we adopt a profile with γ ¼ 1.2. The choice of γ ¼ 1.0 versus 1.2 does not qualitatively affect our primary conclusions.…”

Handling the uncertainties in the Galactic Dark Matter distribution for particle Dark Matter searches

“…It should be mentioned, nonetheless, that the tension with dwarfs constraints can also be further relieved if more conservative estimates of the DM content of the dwarfs is adopted [86], or, similarly, if a more conservative analysis of the gamma-ray background at the dwarfs positions is performed [87,88]. Simplified attempts to take into account the DM distribution uncertainties for the GCE excess have been performed in [89][90][91][92]. In [89], similarly to here, variations with respect to the Galactic parameters are studied, but without performing a formal marginalization.…”

Impact of Cosmic-Ray Physics on Dark Matter Indirect Searches

“…At present, dSph gamma-ray upper-bounds are remarkably probing the benchmark thermal relic scenario within the WIMP mass window [305][306][307][308]. Such upper limits may be at odds with naive DM interpretations of the GC excess [309,310], while depending crucially on the estimated Advances in High Energy Physics Counts-Model, E  = 1 − GeV Counts-Model, E  = 1 − 10 GeV Counts-Model, E  = 1 − 10 GeV Figure 4: Importance of the cosmic-ray contribution to the galactic center excess at few GeV from the analysis of Fermi-LAT data. The three panels refer to the residual photon count maps discussed in [245].…”