The shapes of Milky-Way-mass galaxies with Self-Interacting Dark Matter

The cold dark matter plus dark energy (ΛCDM) cosmological model has been successful at reproducing the large-scale structure of the Universe. However, on length scales smaller than ~1 Mpc and halo masses smaller than ~10¹¹ M_⊙, this framework is challenged by observations that halos are less centrally dense than predicted. One way to reconcile these observations with theoretical predictions, without affecting the large-scale structure, is to consider self-interacting dark matter (SIDM) models. In order to incorporate the effects of both baryonic and SIDM interactions, we use the Feedback in Realistic Environments (FIRE-2) suite of Milky-Way-mass galaxies on a cosmological background and compare the shapes of the main dark matter halo predicted by SIDM simulations (at interaction cross-sections σ/m of 1 and 10 cm² g^-1) with CDM simulations using the same initial conditions.