Shapes and density profiles of haloes in self-interacting dark matter cosmologies

We use cosmological simulation to test the differences of halo properties on the mass range that goes from Milky-Way-like to massive elliptical galaxies in CDM and SIDM models. We use two distinct SIDM models, one with constant cross-section (σ/m = 1 cm^2 /g) and one with a velocity-dependent cross-section. The simulation set is made of 6 runs in total, which simulate the same volume of 50 Mpc^3, in CDM and the two SIDM models; moreover, for each of those, a DM-only and a full-hydrodynamic version is available. In particular, we focus on the analysis of density profiles and halo shapes at z = 0. We split our sample into three mass bins to compare and average the features of haloes of comparable mass. From DM-only simulations we find: 1) both SIDM models produce a central core in density profiles regardless of the halo mass; 2) both SIDM models make DM haloes rounder than in CDM counterpart for each mass bin. From full-hydrodynamic simulations, we find that the inclusion of baryonic effects can modify these properties. Both for the density profiles and the halo shapes the baryon effects make the differences between the DM models less pronounced than in the DM-only case. Moreover, we find that the average final properties of the density profiles in full-hydrodynamic simulations depend on the considered mass bin: the most massive shows a cored profile in the SIDM runs, while the less massive one shows a cuspier profile than in CDM. For the intermediate-mass bin, we find no differences in the density profile between the models. Regarding the halo shapes, we find that the haloes in the SIDM models are more spherical than in the CDM counterpart also with the inclusion of the baryonic effects. However, while the differences between DM models in the density profiles are visible only at small radii (r < 10 kpc/h), we show that SIDM haloes remain more spherical than in CDM even in more external regions (r ∼ 60 − 100 kpc/h).