And In The Darkness Unbind Them: High-Resolution Simulations of Dark Matter Subhalo Disruption in a Milky Way-like Tidal Field

Abstract

We compare the results of high-resolution simulations of individual dark matter subhalos evolving in external tidal fields with and without baryonic bulge and disk components, where the average dark matter particle mass is three orders of magnitude smaller than cosmological zoom-in simulations of galaxy formation. The Via Lactea II simulation is used to setup our initial conditions and provides a basis for our simulations of subhalos in a dark matter-only tidal field, while an observationally motivated model for the Milky Way is used for the tidal field that is comprised of a dark matter halo, a stellar disk, and a stellar bulge. Our simulations indicate that including stellar components in the tidal field results in the number of subhalos in Milky Way-like galaxies being only $65\%$ of what is predicted by $Λ$ Cold Dark Matter ($Λ$CDM). For subhalos with small pericentres $(r_p \lesssim 25$ kpc), the subhalo abundance is reduced further to $40\%$, with the surviving subhalos being less dense and having a tangentially-anisotropic orbital distribution. Conversely, subhalos with larger pericentres are minimally affected by the inclusion of a stellar component in the tidal field, with the total number of outer subhalos $\approx 75\%$ of the $Λ$CDM prediction. The densities of outer subhalos are comparable to predictions from $Λ$CDM, with the subhalos having an isotropic distribution of orbits. These ratios are higher than those found in previous studies that include the effects baryonic matter, which are affected by spurious disruption caused by low resolution.