Dark matter substructure cannot explain properties of the Fermi Galactic Centre excess

Abstract

An excess of gamma rays has been identified at the centre of the Milky Way, and annihilation of dark matter has been posited as a potential source. This hypothesis faces significant challenges: difficulty characterizing astrophysical backgrounds, the need for a non-trivial adiabatic contraction of the inner part of the Milky Way's dark matter halo, and recent observations of photon clustering, which suggest that the majority of the excess is due to unresolved point sources. Here we point out that the apparent point-like nature of the emission rules out the dark matter interpretation of the excess entirely. Attempting to model the emission with dark matter point sources either worsens the problem with the inner slope, requires an unrealistically large minihalo fraction toward the Galactic Centre, or overproduces the observed emission at higher latitudes.

The Fermi–LAT Galactic Center Excess: Evidence of Annihilating Dark Matter?

“…Although DM substructures could contribute to the discrete emission, in standard scenarios they do not fully account for the observed point-like structure claimed by these results(93).…”

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

“…Recall that without the H I template, the Bayes factor in preference for PSs was 2 ln BF ≈ 15. The equivalent results when including the cosmic-ray product version of the H I are the slightly higher values of 15,16,17,16, and 17. Interestingly, this seems to suggest that while the inclusion of the H I template provides a substantially better fit to the data, it has little effect (and, if anything, a positive effect) on the evidence for GCEcorrelated PSs.…”

“…The Fermi Galactic Center excess (GCE) is an approximately spherically symmetric excess of ∼GeV gammarays observed in the inner regions of the Milky Way by the Fermi Large Area Telescope (LAT). While the GCE is subdominant compared to diffuse cosmic-ray emission in this region of sky, the statistical and systematic robustness of the excess to variations in dataset and foreground models has been firmly established [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. The GCE has attracted significant attention because it may arise from the annihilation of a near-thermal dark matter (DM) candidate with mass on the order of ∼10-100 GeV.…”

Two component WIMP–FImP dark matter model with singlet fermion, scalar and pseudo scalar

“…However, apart from dark matter annihilation, the gamma ray excess at GC in the range 1-3 GeV can also be explained by various non-DM phenomena, such as a contribution from point sources near GC [61] or in terms of millisecond pulsars [62]. The study by Clark et al [155] also rules out the idea that the point like sources are dark matter substructures. However, in a recent work the Fermi-LAT and DES collaborations have performed an analysis of γ -ray data with 45 confirmed dwarf spheroidals (dSphs) [65].…”