Fitts et al., available on arXiv

Abstract: We present a suite of FIRE-2 cosmological zoom-in simulations of isolated field dwarf galaxies, all with masses of M_halo ~ 10^10 Msun at z=0, across a range of dark matter models. For the first time, we compare how both self-interacting dark matter (SIDM) and/or warm dark matter (WDM) models affect the assembly histories as well as the central density structure in fully hydrodynamical simulations of dwarfs. Overall, the inclusion of self-interactions does little to affect the mass assembly of these halos (both dark matter and baryonic), while WDM models generally delay dark matter halo formation and reduce galaxies’ stellar masses at z=0. Dwarfs with smaller stellar half-mass radii (r_1/2<500 pc) have lower sigma_star/V_max ratios, reinforcing the idea that smaller dwarfs may reside in halos that are more massive than is naively expected. Surprisingly, the majority of dwarfs simulated with self-interactions (regardless of the warmth of the dark matter) actually experience contraction of their inner density profiles with the addition of baryons relative to the cores produced in dark-matter-only runs, though the simulated dwarfs are always less centrally dense than in LambdaCDM. Our V_1/2-r_1/2 relation is overall consistent with observations of Local Field dwarfs, though compact objects such as Tucana provide a unique challenge. Spatially-resolved rotation curves in the central regions (<400 pc) of small dwarfs could provide a way to distinguish between CDM, WDM, and SIDM: at the masses probed in this simulation suite, cored density profiles in dwarfs with small r_1/2 values can only originate from dark matter self-interactions.