The abundance of satellite galaxies in the inner region of $\Lambda$CDM Milky Way sized haloes

TL;DR

This study combines high-resolution simulations and semi-analytical models to investigate the discrepancy between predicted and observed satellite galaxies in the Milky Way's inner region, revealing the impact of the stellar disk on satellite survivability.

Contribution

It introduces a combined simulation and modeling approach to explain the observed satellite galaxy count by including the effects of the Milky Way's stellar disk.

Findings

Model predicts about 20 inner satellites per halo, more than observed.

Including a stellar disk disrupts 40% of satellites, reducing the count to match observations.

The presence of the stellar disk is crucial in explaining satellite survivability.

Abstract

The concordance $\Lambda$CDM cosmology predicts tens of satellite galaxies distributed in the inner region ($<40\ \lkpc$) of the Milky Way (MW), yet at most $12$ were discovered at present day, including 3 discovered very recently by Dark Energy Survey (DES) and 5 from other surveys (e.g. PanSTARRS, MagLiteS). We use $5$ ultra-high resolution simulations of MW sized dark matter haloes from the $\aqua$ project, combined with $\galf$ semi-analytical galaxy formation model, to investigate properties of the model satellite galaxy population inside $40\ \lkpc$ of MW sized haloes. On average, in each halo this model predicts about $20$ inner satellite galaxies, among them $5$ are comparable to the classic satellites in the luminosity, these are in stark contrast to the corresponding numbers in observations. We further investigate the survivability of these model inner satellites in the presence of a central stellar disk with a set of ideal simulations. These are done by re-evolving a quarter (30) of the whole $\aqua$ inner satellite galaxies (121) by including a static disk potential in addition to the MW halo. Our finding is that the additional disk completely disrupt 40 percents of these satellites and results in $14$ satellite galaxies within the $40\ \lkpc$ of each $\aqua$ at the end, in reasonably well agreement with observations.