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

TL;DR

This study searches for gamma-ray emissions from eight new dwarf spheroidal galaxy candidates discovered by DES using Fermi-LAT data, finding no significant signals but noting a weak excess near Tucana III that warrants further investigation.

Contribution

First search for gamma-ray emission from eight new DES dwarf galaxy candidates using Fermi-LAT data, providing constraints on dark matter annihilation and identifying a potential weak signal near Tucana III.

Findings

No significant gamma-ray signals detected from the eight candidates.

Constraints on dark matter annihilation are comparable to previous bounds for certain masses.

A weak gamma-ray excess observed near Tucana III suggests possible dark matter signal.

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 $\gamma-$ray emissions from the directions of these eight newly discovered dSph galaxy candidates. No statistically significant $\gamma-$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 $\chi\chi \rightarrow \tau^{+}\tau^{-}$ 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 $m_\chi>250$ 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 $\gamma-$ray signal and its peak test statistic (TS) value for the dark matter annihilation channel $\chi\chi\rightarrow \tau^{+}\tau^{-1}$ is $\approx 6.7$ at $m_\chi \sim 15$ 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.