Searching for Dark Matter Annihilation in the Smith High-Velocity Cloud

TL;DR

This study uses gamma-ray data to search for dark matter annihilation signals in the Smith Cloud, setting limits on dark matter properties and comparing its potential as a target to dwarf galaxies.

Contribution

It demonstrates that the Smith Cloud can be a competitive target for dark matter searches and provides new constraints on dark matter annihilation cross sections.

Findings

No gamma-ray excess detected from the Smith Cloud.

Limits exclude the canonical thermal relic cross section for dark matter masses below 30 GeV.

Constraints depend on assumptions about the dark matter density profile.

Abstract

Recent observations suggest that some high-velocity clouds may be confined by massive dark matter halos. In particular, the proximity and proposed dark matter content of the Smith Cloud make it a tempting target for the indirect detection of dark matter annihilation. We argue that the Smith Cloud may be a better target than some Milky Way dwarf spheroidal satellite galaxies and use gamma-ray observations from the Fermi Large Area Telescope to search for a dark matter annihilation signal. No significant gamma-ray excess is found coincident with the Smith Cloud, and we set strong limits on the dark matter annihilation cross section assuming a spatially-extended dark matter profile consistent with dynamical modeling of the Smith Cloud. Notably, these limits exclude the canonical thermal relic cross section ($\sim 3\times10^{-26}{\rm cm}^{3}{\rm s}^{-1}$) for dark matter masses $\lesssim 30$ GeV annihilating via the $b \bar b$ or $\tau^{+}\tau^{-}$ channels for certain assumptions of the dark matter density profile; however, uncertainties in the dark matter content of the Smith Cloud may significantly weaken these constraints.