Search for gamma-ray emission from eight dwarf spheroidal galaxy candidates discovered in Year Two of Dark Energy Survey with Fermi-LAT data

Abstract

Very recently the Dark Energy Survey (DES) Collaboration has released their second group of Dwarf spheroidal (dSph) galaxy candidates. With the publicly-available Pass 8 data of Fermi-LAT we search for $γ-$ray emissions from the directions of these eight newly discovered dSph galaxy candidates. No statistically significant $γ-$ray signal has been found in the combined analysis of these sources. With the empirically estimated J-factors of these sources, the constraint on the annihilation channel of $χχ\rightarrow τ^{+}τ^{-}$ is comparable to the bound set by the joint analysis of fifteen previously known dSphs with kinematically constrained J-factors for the dark matter mass $m_χ>250$ GeV. In the direction of Tucana III (DES J2356-5935), one of the nearest dSph galaxy candidates that is $\sim 25$ kpc away, there is a weak $γ-$ray signal and its peak test statistic (TS) value for the dark matter annihilation channel $χχ\rightarrow τ^{+}τ^{-1}$ is $\approx 6.7$ at $m_χ\sim 15$ GeV. The significance of the possible signal likely increases with time. More data is highly needed to pin down the physical origin of such a GeV excess.

To appear in Phys. Rev. D, Fig.4 has been updated and main conclusions are unchanged