Search for Gamma-Ray Emission from DES Dwarf Spheroidal Galaxy Candidates with Fermi-LAT Data (1503.02632v3)

Abstract: Due to their proximity, high dark-matter content, and apparent absence of non-thermal processes, Milky Way dwarf spheroidal satellite galaxies (dSphs) are excellent targets for the indirect detection of dark matter. Recently, eight new dSph candidates were discovered using the first year of data from the Dark Energy Survey (DES). We searched for gamma-ray emission coincident with the positions of these new objects in six years of Fermi Large Area Telescope data. We found no significant excesses of gamma-ray emission. Under the assumption that the DES candidates are dSphs with dark matter halo properties similar to the known dSphs, we computed individual and combined limits on the velocity-averaged dark matter annihilation cross section for these new targets. If the estimated dark-matter content of these dSph candidates is confirmed, they will constrain the annihilation cross section to lie below the thermal relic cross section for dark matter particles with masses < 20 GeV annihilating via the b-bbar or tau+tau- channels.

• The paper presents a search for gamma-ray emissions in eight DES dwarf spheroidal candidates using six years of Fermi-LAT data.
• It employs maximum-likelihood methods to set robust upper limits on dark matter annihilation cross-sections for bb and τ⁺τ⁻ channels.
• The null detection refines indirect dark matter search strategies by constraining annihilation cross-sections below thermal relic values for particles under 20 GeV.

Analysis of Gamma-Ray Emissions from Dwarf Spheroidal Galaxy Candidates

The paper presents a comprehensive analysis of gamma-ray emissions associated with newly discovered dwarf spheroidal (dSph) galaxy candidates from the Dark Energy Survey (DES), utilizing six years of data from the Fermi Large Area Telescope (LAT). The primary motivation for the paper is to enhance indirect dark matter (DM) detection strategies by analyzing dSph galaxies, which are optimal targets due to their proximity, high DM content, and minimal non-thermal activities.

Research Overview

The paper involved searching for gamma-ray emissions coincident with the positions of eight newly identified DES dSph candidates. These candidates were subjected to an analysis leveraging six years of data from the Fermi-LAT, yet no gamma-ray excess was observed in association with these objects.

Methodology

The research deployed maximum-likelihood techniques to estimate limits on the velocity-averaged DM annihilation cross-section, assuming halo properties akin to established dSphs. By analyzing a targeted region of interest (ROI) using LAT data and focusing on the annihilation channels involving heavy particles like bb and $\tau^+ \tau^-$, the paper reports no significant gamma-ray emissions reflective of DM annihilation.

Strong Numerical Results

The paper provides robust upper limits on the cross-section for annihilation to bb and $\tau^+ \tau^-$ channels. Significantly, these limits constrain the annihilation cross-section values to be lower than the thermal relic cross-section for DM particles less than 20 GeV under certain assumptions.

Implications and Speculation

Theoretical implications emphasize the need for further spectroscopic and kinematic studies. Practically, these findings imply no detectable gamma-ray emissions from the examined dSph candidates within current sensitivity limits, which could refine target selection in subsequent DM indirect detection efforts.

The lack of detected gamma-ray emission could suggest either a non-DM nature for the observed excesses or potentially lower-than-anticipated J-factors assuming the DM halo profiles of known dSphs. Future studies may benefit from enhanced sensitivity and additional candidates from other surveys, potentially leading to the detection of DM signals.

Concluding Thoughts

The investigation did not result in the detection of significant gamma-ray emissions from the DES dSph candidates, which maintains the ambiguity surrounding their DM halo properties. As indirect searches advance, findings such as these play a critical role in refining detection methodologies and understanding the characteristics of DM-dominated regions in our universe. The integration of new dSph candidates into indirect searches using Fermi-LAT enhances the prospect of detecting DM signals alongside continued methodological improvements in observational practices.