Baryons Shaping Dark Matter Haloes

New Paper: Baryons Shaping Dark Matter Haloes. Cataldi et al. 2021




Abstract

In the last decade, it has been well-established that baryonic processes play a crucial role in the evolution of dark matter (DM) haloes. Nevertheless, the details of this intricate coevolution are still not fully understood. In this work we aim at investigating the effects of baryons on the DM haloes structure, focusing on the correlation between the presence and importance of stellar discs and the halo shapes. We study the properties of a subsample of DM haloes from Fenix and EAGLE cosmological simulations, hosting well-resolved galaxies. We inspect the central regions of haloes, comparing the hydrodynamic runs and their dark matter only (DMo) counterparts. Our results indicate that baryons have a significant impact on the shape of the inner halo, mainly within ~20 percent of the virial radius. As reported before haloes found to be more spherical when hosting baryons. While the impact of baryons depends on the mass of the haloes, we also find a trend with morphology which suggests that the way baryons are assembled is also relevant in agreement with previous works. Our findings also indicate that disc galaxies preferentially form in haloes whose DMo counterparts were originally more spherical and with stronger velocity anisotropy. The presence of baryons alter the orbital structure of the DM particles of the haloes, which show a decrease in the DM velocity anisotropy, towards more tangentially biased DM orbits. This relative decrease is weaker in the case of disc-dominated galaxies. Our results point out to a cosmological connection between the final morphology of galaxies and the intrinsic properties of their DM haloes, which gets reinforced by the growth of the discs.