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 $\ensuremath{\gamma}$-ray emissions from the directions of these eight newly discovered dSph galaxy candidates. No statistically significant $\ensuremath{\gamma}$-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 $\ensuremath{\chi}\ensuremath{\chi}\ensuremath{\rightarrow}{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ 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 ${m}_{\ensuremath{\chi}}>250\text{ }\text{ }\mathrm{GeV}$. In the direction of Tucana III (DES J2356-5935), one of the nearest dSph galaxy candidates that is $\ensuremath{\sim}25\text{ }\text{ }\mathrm{kpc}$ away, there is a weak $\ensuremath{\gamma}$-ray signal and its peak test statistic (TS) value for the dark matter annihilation channel $\ensuremath{\chi}\ensuremath{\chi}\ensuremath{\rightarrow}{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}1}$ is $\ensuremath{\approx}6.7$ at ${m}_{\ensuremath{\chi}}\ensuremath{\sim}15\text{ }\text{ }\mathrm{GeV}$. 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.