SatGen -- II. Assessing the impact of a disc potential on subhalo populations

TL;DR

This study uses a semi-analytical model to assess how galactic discs influence dark matter subhalo populations, finding that disc mass slightly reduces subhalo abundance mainly near the galaxy center, with minimal impact on overall counts.

Contribution

The paper introduces the SatGen semi-analytical model to accurately evaluate disc effects on subhalo demographics, overcoming limitations of numerical simulations.

Findings

Subhalo abundance is mainly affected by disc mass, not other properties.

Within the virial radius, subhalo counts decrease by less than 10% due to the disc.

Within 50 kpc, subhalo counts are reduced by approximately 30%.

Abstract

The demographics of dark matter substructure depend sensitively on the nature of dark matter. Optimally leveraging this probe requires accurate theoretical predictions regarding the abundance of subhaloes. These predictions are hampered by artificial disruption in numerical simulations, by large halo-to-halo variance, and by the fact that the results depend on the baryonic physics of galaxy formation. In particular, numerical simulations have shown that the formation of a central disc can drastically reduce the abundance of substructure compared to a dark matter-only simulation, which has been attributed to enhanced destruction of substructure due to disc shocking. We examine the impact of discs on substructure using the semi-analytical subhalo model SatGen, which accurately models the tidal evolution of substructure free of the numerical disruption that still hampers $N$-body simulations. Using a sample of 10,000 merger trees of Milky Way-like haloes, we study the demographics of subhaloes that are evolved under a range of composite halo-disc potentials with unprecedented statistical power. We find that the overall subhalo abundance is relatively insensitive to properties of the disc aside from its total mass. For a disc that contains $5\%$ of $M_\mathrm{vir}$, the mean subhalo abundance within $r_\mathrm{vir}$ is suppressed by ${\lesssim}10\%$ relative to the no-disc case, a difference that is dwarfed by halo-to-halo variance. For the same disc mass, the abundance of subhaloes within 50 kpc is reduced by ${\sim}30\%$. We argue that the disc mainly drives excess mass loss for subhaloes with small pericentric radii and that the impact of disc shocking is negligible.