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

We examine the properties of satellites found in high-resolution simulations of the Local Group (LG). We use constrained simulations designed to reproduce the main dynamical features that characterize the local neighbourhood, i.e. within tens of Mpc around the LG. Specifically, an 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 modelled 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(sub) > 2 x 10(8) h(-1)M(circle dot) subhaloes in hydrodynamic simulations are more radially concentrated than those in simulations without 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 than their dark matter counterparts.