Motivations for a large self-interacting dark matter cross-section from Milky Way satellites

ABSTRACT We explore the properties of Milky Way (MW) subhaloes in self-interacting dark matter models for moderate cross-sections of 1–5 cm2 g−1 using high-resolution zoom-in N-body simulations. We include the gravitational potential of a baryonic disc and bulge matched to the MW, which is critical for getting accurate predictions. The predicted number and distribution of subhaloes within the host halo are similar for 1 and 5 cm2 g−1 models, and they agree with observations of MW satellite galaxies only if subhaloes with peak circular velocity over all time 7 km s−1 are able to form galaxies. We do not find distinctive signatures in the pericentre distribution of the subhaloes that could help distinguish the models. Using an analytical model to extend the simulation results, we are able to show that subhaloes in models with cross-sections between 1 and 5 cm2 g−1 are not dense enough to match the densest ultrafaint and classical dwarf spheroidal galaxies in the MW. This motivates exploring velocity-dependent cross-sections with values larger than 5 cm2 g−1 at the velocities relevant for the satellites such that core collapse would occur in some of the ultrafaint and classical dwarf spheroidals.