Constrained simulations of the Local Group: on the radial distribution of substructures

TL;DR

This study uses constrained high-resolution simulations of the Local Group to analyze how baryonic physics influences the radial distribution and density of satellite subhaloes, revealing that gas physics leads to more concentrated and denser substructures.

Contribution

It provides the first detailed comparison of satellite subhalo properties in constrained Local Group simulations with and without baryonic physics, highlighting the impact of gas dynamics on subhalo distribution.

Findings

Hydrodynamic subhaloes are more radially concentrated than dark matter-only ones.

Baryons increase subhalo central density, reducing tidal mass loss.

Enhanced density leads to more effective dynamical friction, drawing subhaloes inward.

Abstract

We examine the properties of satellites found in high resolution simulations of the local group. We use constrained simulations designed to reproduce the main dynamical features that characterize the local neighborhood, i.e. within tens of Mpc around the Local Group (LG). Specifically, a LG-like object is found located within the 'correct' dynamical environment and consisting of three main objects which are associated with the Milky Way, M31 and M33. By running two simulations of this LG from identical initial conditions - one with and one without baryons modeled hydrodynamically - we can quantify the effect of gas physics on the $z=0$ population of subhaloes in an environment similar to our own. We find that above a certain mass cut, $M_{\rm sub} > 2\times10^{8}h^{-1} M_{\odot}$ subhaloes in hydrodynamic simulations are more radially concentrated than those in simulations with out gas. This is caused by the collapse of baryons into stars that typically sit in the central regions of subhaloes, making them denser. The increased central density of such a subhalo, results in less mass loss due to tidal stripping than the same subhalo simulated with only dark matter. The increased mass in hydrodynamic subhaloes with respect to dark matter ones, causes dynamical friction to be more effective, dragging the subhalo towards the centre of the host. This results in these subhaloes being effectively more radially concentrated then their dark matter counterparts.