Dark matter subhalos and unidentified sources in the Fermi 3FGL source catalog

TL;DR

This study assesses the likelihood of detecting dark matter subhalos as gamma-ray sources with Fermi LAT, predicting at most about 10 such subhalos under optimistic WIMP assumptions, and constrains WIMP properties based on the 3FGL catalog.

Contribution

It provides updated predictions for dark matter subhalo detectability using the Via Lactea II simulation and derives new upper limits on WIMP annihilation cross-section from Fermi LAT data.

Findings

At most 10 subhalos predicted in 3FGL under optimistic assumptions

Predictions are lower than previous studies due to updated simulations

Constraints on WIMP annihilation cross-section are competitive with other indirect searches

Abstract

If dark matter consists of weakly interacting massive particles (WIMPs), dark matter subhalos in the Milky Way could be detectable as gamma-ray point sources due to WIMP annihilation. In this work, we perform an updated study of the detectability of dark matter subhalos as gamma-ray sources with the Fermi Large Area Telescope (Fermi LAT). We use the results of the Via Lactea II simulation, scaled to the Planck 2015 cosmological parameters, to predict the local dark matter subhalo distribution. Under optimistic assumptions for the WIMP parameters --- a 40 GeV particle annihilating to $b\bar{b}$ with a thermal cross-section, as required to explain the Galactic center GeV excess --- we predict that at most $\sim 10$ subhalos might be present in the third Fermi LAT source catalog (3FGL). This is a smaller number than has been predicted by prior studies, and we discuss the origin of this difference. We also compare our predictions for the detectability of subhalos with the number of subhalo candidate sources in 3FGL, and derive upper limits on the WIMP annihilation cross-section as a function of the particle mass. If a dark matter interpretation could be excluded for all 3FGL sources, our constraints would be competitive with those found by indirect searches using other targets, such as known Milky Way satellite galaxies.