Dark Matter Annihilation in Substructures Revised

TL;DR

This paper assesses the detectability of dark matter annihilation signals in Milky Way substructures with upcoming gamma-ray satellites, highlighting how assumptions on substructure distribution affect detection prospects and constraining micro-clump scenarios.

Contribution

It provides revised estimates for dark matter substructure detection prospects, considering extreme assumptions and realistic constraints from gamma-ray background data.

Findings

Detection prospects vary from zero to hundreds of sources depending on particle physics parameters.

Only a few large mass substructures are detectable under typical dark matter models.

Micro-clump detection scenarios are strongly constrained by existing gamma-ray background measurements.

Abstract

Upcoming $\gamma$-ray satellites will search for Dark Matter annihilations in Milky Way substructures (or 'clumps'). The prospects for detecting these objects strongly depend on the assumptions made on the distribution of Dark Matter in substructures, and on the distribution of substructures in the Milky Way halo. By adopting simplified, yet rather extreme, prescriptions for these quantities, we compute the number of sources that can be detected with upcoming experiments such as GLAST, and show that, for the most optimistic particle physics setup ($m_\chi=40$ GeV and annihilation cross section $\sigma v = 3 \times 10^{-26}$ cm$^3$ s$^{-1}$), the result ranges from zero to $\sim$ hundred sources, all with mass above $10^{5}M\odot$. However, for a fiducial DM candidate with mass $m_\chi=100$ GeV and $\sigma v = 10^{-26}$ cm$^3$ s$^{-1}$, at most a handful of large mass substructures can be detected at $5 \sigma$, with a 1-year exposure time, by a GLAST-like experiment. Scenarios where micro-clumps (i.e. clumps with mass as small as $10^{-6}M\odot$) can be detected are severely constrained by the diffuse $\gamma$-ray background detected by EGRET.