A Search for Dark Matter Annihilation in Stellar Streams with the Fermi-LAT

TL;DR

This study uses nearly 15 years of Fermi-LAT gamma-ray data to search for dark matter annihilation signals in stellar streams, setting the first constraints on WIMP properties from these objects and demonstrating their potential for future dark matter research.

Contribution

The paper is the first to analyze stellar streams for dark matter signals using Fermi-LAT data, establishing initial constraints on WIMP annihilation cross-sections from these structures.

Findings

No gamma-ray emission detected from any streams.

Constraints are up to 10 times above the thermal relic cross-section.

Systematic uncertainties can vary constraints by orders of magnitude.

Abstract

Stellar streams are remnants of globular clusters or dwarf galaxies that have been tidally disrupted by the gravitational potential of their host galaxy. Streams originating from dwarfs can be particularly compelling targets for indirect dark matter (DM) searches, as dwarfs are believed to be highly DM-dominated systems. Although these streams are expected to lose most of their DM during the tidal stretching process, a significant amount may still remain in their core. If DM is composed of WIMPs, their annihilation within the streams' cores could produce a detectable gamma-ray signal. In this study, we analyze nearly 15 years of data from the Large Area Telescope aboard NASA's Fermi satellite (Fermi-LAT) to search for potential WIMP annihilation signals from the direction of 11 stellar streams selected using DM-motivated criteria. No gamma-ray emission is detected from any of the streams in our sample. In the absence of a signal, we place the first constraints on the WIMP parameter space based on these objects for two representative annihilation channels. Individual DM limits are first computed and then combined across all streams. The most reliable combined constraints, derived from a golden sample and using a benchmark description of their DM content, are $O(10)$ times above the thermal relic cross-section for the $bb$ and $\tau^+\tau^-$ annihilation channels. We also explore how these constraints vary under more conservative or optimistic yet realistic assumptions, finding variations of up to a few orders of magnitude. This large systematic uncertainty stems from key model limitations, which can and should be addressed in future observations and simulations to produce more robust DM limits from streams. Despite uncertainties, this study demonstrates the feasibility of using stellar streams for DM searches and highlights their significant potential to uncover the properties of DM particles.