Perspective of Galactic dark matter subhalo detection on Fermi from the EGRET observation

TL;DR

This paper assesses the potential for Fermi to detect dark matter subhaloes based on EGRET gamma-ray observations, predicting detection of dozens to hundreds of subhaloes, with uncertainties mainly from subhalo mass distribution.

Contribution

It provides a model-independent prediction of dark matter subhalo detectability by Fermi, accounting for uncertainties in subhalo mass functions and observational factors.

Findings

Fermi could detect 10-300 dark matter subhaloes in a 1-year survey.

Detection estimates are independent of dark matter particle physics assumptions.

Main uncertainty arises from the subhalo mass function (point-like vs diffuse-like).

Abstract

The perspective of the detectability of Galactic dark matter subhaloes on the Fermi satellite is investigated in this work. Under the assumptions that dark matter annihilation accounts for the "GeV excess" of the Galactic diffuse $\gamma$-rays discovered by EGRET and the $\gamma$-ray flux is dominated by the contribution from subhaloes of dark matter, we calculate the expected number of dark matter subhaloes that Fermi may detect. We show that Fermi may detect a few tens to several hundred subhaloes in 1-year all sky survey. Since EGRET observation is taken as a normalization, this prediction is independent of the particle physics property of dark matter. The uncertainties of the prediction are discussed in detail. We find that the major uncertainty comes from the mass function of subhaloes, i.e., whether the subhaloes are "point like" (high-mass rich) or "diffuse like" (low-mass rich). Other uncertainties like the background estimation and the observational errors will contribute a factor of $2\sim 3$.