On The Gamma-Ray Emission From Reticulum II and Other Dwarf Galaxies

TL;DR

This paper analyzes gamma-ray data from dwarf galaxies, confirming an excess from Reticulum II that could be linked to dark matter, and improves detection methods using multi-wavelength catalogs for better significance estimation.

Contribution

It provides a new analysis confirming gamma-ray excess from Reticulum II and introduces improved calibration techniques using multi-wavelength data.

Findings

Gamma-ray excess detected from Reticulum II with 3.2 sigma significance.

Spectral shape of the excess is compatible with Galactic Center signal.

Enhanced calibration method reduces false positives by avoiding unresolved sources.

Abstract

The recent discovery of ten new dwarf galaxy candidates by the Dark Energy Survey (DES) and the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) could increase the Fermi Gamma-Ray Space Telescope's sensitivity to annihilating dark matter particles, potentially enabling a definitive test of the dark matter interpretation of the long-standing Galactic Center gamma-ray excess. In this paper, we compare the previous analyses of Fermi data from the directions of the new dwarf candidates (including the relatively nearby Reticulum II) and perform our own analysis, with the goal of establishing the statistical significance of any gamma-ray signal from these sources. We confirm the presence of an excess from Reticulum II, with a spectral shape that is compatible with the Galactic Center signal. The significance of this emission is greater than that observed from 99.84% of randomly chosen high-latitude blank-sky locations, corresponding to a local detection significance of 3.2 sigma. We improve upon the standard blank-sky calibration approach through the use of multi-wavelength catalogs, which allow us to avoid regions that are likely to contain unresolved gamma-ray sources.