Search for gamma-ray emission from the nearby dwarf spheroidal galaxies with 9 years of Fermi-LAT data

TL;DR

This study searches for gamma-ray signals from nearby dwarf spheroidal galaxies using 9 years of Fermi-LAT data, finding weak excesses and a combined signal that could suggest dark matter annihilation.

Contribution

First comprehensive analysis of gamma-ray emission from 12 nearby dwarf galaxies with Fermi-LAT data, indicating potential dark matter signals.

Findings

Weak gamma-ray excesses in some dwarf galaxies.

Peak TS value of 13.5 for Reticulum II suggests possible dark matter annihilation.

Combined analysis yields >4σ significance for gamma-ray signal.

Abstract

In this work, we search for $\gamma$-ray emission from the directions of some nearby Milky Way dwarf spheroidal galaxies (dSphs) and candidates with the publicly-available Pass 8 data of Fermi-LAT. Our sample includes 12 sources with the distances $<50$ kpc. Very weak $\gamma$-ray excesses ($\sim 2\sigma$) are found in some dSphs/candidates, consistent with that reported in the previous literature. Intriguingly, the peak test statistic (TS) value of the weak emission from the direction of Reticulum II rises continually. If interpreted as dark matter (DM) annihilation, the peak TS value is 13.5 for the annihilation channel of $\chi\chi \rightarrow \tau^{+}\tau^{-}$ and the DM mass of $m_\chi \sim 16$ GeV. The combination of all these nearby sources yields a more significant (with local significance $> 4\sigma$) $\gamma$-ray signal.