A Search for Dark Matter Annihilation in Galaxy Groups

TL;DR

This study uses extensive gamma-ray data and galaxy group catalogs to search for dark matter annihilation signals in extragalactic halos, setting new constraints on dark matter properties.

Contribution

It introduces a method combining galaxy group data with gamma-ray observations to constrain dark matter annihilation, including a catalog of galaxy groups with inferred properties.

Findings

No significant dark matter signal detected.

Excluded thermal relic cross sections below ~30 GeV for the bbar channel.

Results increase tension with the Galactic Center excess interpretation.

Abstract

We use 413 weeks of publicly-available $\textit{Fermi}$ Pass 8 gamma-ray data, combined with recently-developed galaxy group catalogs, to search for evidence of dark matter annihilation in extragalactic halos. In our study, we use luminosity-based mass estimates and mass-to-concentration relations to infer the $J$-factors and associated uncertainties for hundreds of galaxy groups within a redshift range $z \lesssim 0.03$. We employ a conservative substructure boost-factor model, which only enhances the sensitivity by an $\mathcal{O}(1)$ factor. No significant evidence for dark matter annihilation is found and we exclude thermal relic cross sections for dark matter masses below $\sim$30 GeV to 95% confidence in the $b\bar{b}$ annihilation channel. These bounds are comparable to those from Milky Way dwarf spheroidal satellite galaxies. The results of our analysis increase the tension, but do not rule out, the dark matter interpretation of the Galactic Center excess. We provide a catalog of the galaxy groups used in this study and their inferred properties, which can be broadly applied to searches for extragalactic dark matter.