Fermi-LAT observations of gamma-ray emission towards the outer halo of M31. The green dashed circle corresponds to a 300 kpc projected radius centered at M31, for an M31-MW distance of 785 kpc (i.e. the virial radius). Also shown is M31’s population of dwarf galaxies. M31 and M33 are shown with cyan triangles, and the other dwarfs are shown with small green circles. The bright emission along 0 degree latitude corresponds to the disk of the MW.