A Search for Dark Matter Annihilation in Galaxy Groups
  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.
