A Gaia DR2 search for dwarf galaxies towards Fermi-LAT sources: implications for annihilating dark matter

TL;DR

This study used Gaia DR2 data and an advanced deconvolution technique to search for dwarf galaxies near Fermi-LAT sources, finding none and setting limits on their stellar mass, which challenges the dark matter annihilation hypothesis.

Contribution

First application of Gaia DR2 data with XD technique to search for dwarf galaxies near Fermi-LAT sources, providing new constraints on their stellar mass and dark matter origin.

Findings

No dwarf galaxy signatures found in the eight fields.

Detection limits suggest dwarf galaxies have stellar mass less than 10^4 solar masses.

Results challenge the hypothesis that Fermi-LAT sources are due to dark matter annihilation.

Abstract

We make a first attempt to find dwarf galaxies in eight \Fermi-LAT extended, unassociated, source fields using \Gaia\ DR2. We probe previously unexplored heliocentric distances of $d<20$~kpc with an extreme-deconvolution (XD) technique. We find no signature of a dwarf galaxy in any of these fields despite \Gaia's excellent astrometric accuracy. We estimate our detection limits by applying the XD method to mock data, obtaining a conservative limit on the stellar mass of $M_* < 10^4$~M$_{\sun}$ for $d < 20$\, kpc. Such a low stellar mass implies either a low-mass subhalo, or a massive stripped-down subhalo. We use an analytic model for stripped subhalos to argue that, given the sizes and fluxes of the \Fermi-LAT sources, we can reject the hypothesis that they owe to dark matter annihilation.