Indication of Gamma-Ray Emission from the Newly Discovered Dwarf Galaxy Reticulum II.
We present a search for γ-ray emission from the direction of the newly discovered dwarf galaxy Reticulum II. Using Fermi-LAT Collaboration data, we detect a signal that exceeds expected backgrounds between ∼2-10  GeV and is consistent with annihilation of dark matter for particle masses less than a few ×10^{2}  GeV. Modeling the background as a Poisson process based on Fermi-LAT diffuse models, and taking into account trial factors, we detect emission with p value less than 9.8×10^{-5} (>3.7σ). An alternative, model-independent treatment of the background reduces the significance, raising the p value to 9.7×10^{-3} (2.3σ). Even in this case, however, Reticulum II has the most significant γ-ray signal of any known dwarf galaxy. If Reticulum II has a dark-matter halo that is similar to those inferred for other nearby dwarfs, the signal is consistent with the s-wave relic abundance cross section for annihilation.
McWilliams Center for Cosmology, Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
Alex
A
Geringer-Sameth
McWilliams Center for Cosmology, Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
Matthew G
MG
Walker
Department of Physics, Brown University, Providence, Rhode Island 02912, USA.
Savvas M
SM
Koushiappas
Institute of Astronomy, University of Cambridge, Cambridge CB3 0HA, United Kingdom.
Sergey E
SE
Koposov
Institute of Astronomy, University of Cambridge, Cambridge CB3 0HA, United Kingdom.
Vasily
V
Belokurov
Institute of Astronomy, University of Cambridge, Cambridge CB3 0HA, United Kingdom.
Gabriel
G
Torrealba
Institute of Astronomy, University of Cambridge, Cambridge CB3 0HA, United Kingdom.
N Wyn
NW
Evans