High-resolution simulations of dark matter subhalo disruption in a Milky-Way-like tidal field

Abstract

ABSTRACT We compare the results of high-resolution simulations of individual dark matter subhaloes evolving in external tidal fields with and without baryonic bulge and disc 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 subhaloes 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 disc, and a stellar bulge. Our simulations indicate that including stellar components in the tidal field results in the number of subhaloes in Milky-Way-like galaxies being only $65{{\ \rm per\ cent}}$ of what is predicted by Λ cold dark matter (ΛCDM). For subhaloes with small pericentres (rp ≲ 25 kpc), the subhalo abundance is reduced further to $40{{\ \rm per\ cent}}$, with the surviving subhaloes being less dense and having a tangentially anisotropic orbital distribution. Conversely, subhaloes with larger pericentres are minimally affected by the inclusion of a stellar component in the tidal field, with the total number of outer subhaloes $\approx 75{{\ \rm per\ cent}}$ of the ΛCDM prediction. The densities of outer subhaloes are comparable to predictions from ΛCDM, with the subhaloes 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.