Structure of Dark Matter Halos in Illustris: Effect of Baryons

Abstract

We study the effect of baryonic processes on the properties of dark matter (DM) halos in cosmological hydrodynamic simulations over a wide range of masses (M_200 = 110^11 - 310^14 M_sun). Our study is based on the Illustris simulations, a set of hydrodynamical (Illustris) and N-body (Illustris-Dark) cosmological simulations carried out using the moving-mesh code AREPO. We describe the effect of baryons on subhalo demographics, the shape of DM halos as well as their orbital structure, by understanding how halos in Illustris differ from their DM-only counterparts in Illustris-Dark. We find that the condensation of baryons has a large impact on DM properties, including halo mass, concentration, shape and abundance of subhalos. Finally, we examine the structure of DM halos by quantifying the types of orbits (e.g. box or tube orbits) that populate Illustris halos.