The evolution of dwarf galaxy satellites with different dark matter density profiles in the ErisMod simulations. I. The early infalls

Abstract

We present the first simulations of tidal stirring of dwarf galaxies in the Local Group carried out in a cosmological context. We use the ErisDARK simulation of a MW-sized galaxy to identify some of the most massive subhalos ($M_{vir} > 10^8 M_{\odot}$) that fall into the main host before $z=2$. Subhalos are replaced before infall with high-resolution models of dwarf galaxies comprising a faint stellar disk embedded in a dark matter halo. The set of models contains cuspy halos as well as halos with "cored" profiles (with asymptotic inner slope $\gamma = 0.6$). The simulations are then run to $z=0$ with as many as 54 million particles and resolution as small as $\sim 4$ pc using the N-Body code ChaNGa. The stellar components of all satellites are significantly affected by tidal stirring, losing stellar mass and undergoing a morphological transformation towards a pressure supported spheroidal system. However, while some remnants with cuspy halos maintain significant rotational flattening and disk-like features, all the shallow halo models achieve $v/\sigma < 0.5$ and round shapes typical of dSph satellites of the MW and M31. Mass loss is also enhanced in the latter, and remnants can reach luminosities and velocity dispersions as low as those of Ultra Faint Dwarfs (UFDs). We argue that cuspy progenitors must be the exception rather than the rule among satellites of the MW since all the MW and M31 satellites in the luminosity range of our remnants are dSphs, a result matched only in the simulation with "cored" models