The impact of disc disruption on Milky Way satellite counts

TL;DR

This paper investigates how the disruption of satellite galaxies by the Milky Way's stellar disc affects estimates of the total satellite population, highlighting the importance of accounting for this disruption in models.

Contribution

It introduces an N-body simulation and toy model to quantify the impact of disc disruption on satellite counts and distributions, emphasizing the need to consider this effect in predictions.

Findings

High resilience to disc disruption leads to fewer, more concentrated satellites in massive subhaloes.

Low resilience results in more numerous, less concentrated satellites in less massive subhaloes.

Massive subhaloes are particularly vulnerable to disruption due to their radial orbits.

Abstract

Estimates for the total number of Milky Way (MW) satellites are often generated from a combination of the observed number of satellites in surveys, adjustments for the completeness of those surveys, and theoretical expectations from halo assembly modelling. One of the features of this modelling is disruption by the MW stellar disc. We examine the effect of degrees of disc disruption on inferred satellite counts, by means of an N-body simulation of a MW-mass halo plus a toy model for this disruption. We use a fictional all-sky survey to show that high resilience to disc disruption predicts small populations of satellites that are radially very concentrated around the central galaxy and are hosted by massive subhaloes, while low resilience predicts many more satellites with a less concentrated radial distribution and hosted within less massive subhaloes. We show that the most massive subhaloes are particularly susceptible to disruption due to their radial orbits, and in their putative absence galaxy formation must occur in lower mass haloes that have a shallower radial number density profile. We then demonstrate this phenomenon for a combination of the Pan-STARRS and DES surveys. It is therefore necessary to account for uncertainty in the disc disruption radius when making predictions for MW satellite distributions.