Prospective Dark Matter Annihilation Signals From the Sagittarius Dwarf Spheroidal

TL;DR

This study uses high-resolution hydrodynamic simulations to estimate the dark matter annihilation signal from the Sagittarius Dwarf Spheroidal galaxy, revealing lower J-factors than previous estimates and questioning its utility in indirect detection.

Contribution

It introduces a novel simulation-based approach incorporating tidal disruption effects to more accurately estimate the J-factor for Sgr, challenging prior overestimations.

Findings

The simulated J-factor for Sgr is significantly lower than previous estimates.

Most past studies overestimated the dark matter density of Sgr on small scales.

Gamma-ray emissions from Sgr are likely of astrophysical origin, not dark matter annihilation.

Abstract

The Sagittarius Dwarf Spheroidal galaxy (Sgr) is investigated as a target for DM annihilation searches utilising J-factor distributions calculated directly from a high-resolution hydrodynamic simulation of the infall and tidal disruption of Sgr around the Milky Way. In contrast to past studies, the simulation incorporates DM, stellar and gaseous components for both the Milky Way and the Sgr progenitor galaxy. The simulated distributions account for significant tidal disruption affecting the DM density profile. Our estimate of the J-factor value for Sgr, $J_{\text{Sgr}}=1.48\times 10^{10}$ M$_\odot^2$ kpc$^{-5}$ ($6.46\times10^{16}\ \text{GeV}\ \text{cm}^{-5}$), is significantly lower than found in prior studies. This value, while formally a lower limit, is likely close to the true J-factor value for Sgr. It implies a DM cross-section incompatibly large in comparison with existing constraints would be required to attribute recently observed $\gamma$-ray emission from Sgr to DM annihilation. We also calculate a J-factor value using a NFW profile fitted to the simulated DM density distribution to facilitate comparison with past studies. This NFW J-factor value supports the conclusion that most past studies have overestimated the dark matter density of Sgr on small scales. This, together with the fact that the Sgr has recently been shown to emit $\gamma$-rays of astrophysical origin, complicate the use of Sgr in indirect DM detection searches.