The outer stellar halos of galaxies: how radial merger mass deposition, shells, and streams depend on infall-orbit configurations

Abstract

Galaxy mergers are a fundamental part of galaxy evolution. To study the resulting mass distributions of different kinds of galaxy mergers, we present a simulation suite of 36 high-resolution isolated merger simulations, exploring a wide range of parameter space in terms of mass ratios (mu = 1:5, 1:10, 1:50, 1:100) and orbital parameters. We find that mini mergers deposit a higher fraction of their mass in the outer halo compared to minor mergers, while their contribution to the central mass distribution is highly dependent on the orbital impact parameter: for larger pericentric distances we find that the centre of the host galaxy is almost not contaminated by merger particles. We also find that the median of the resulting radial mass distribution for mini mergers differs significantly from the predictions of simple theoretical tidal-force models. Furthermore, we find that mini mergers can increase the size of the host disc significantly without changing the global shape of the galaxy, if the impact occurs in the disc plane, thus providing a possible explanation for extended low-surface brightness disks reported in observations. Finally, we find clear evidence that streams are a strong indication of nearly circular infall of a satellite (with large angular momentum), whereas the appearance of shells clearly points to (nearly) radial satellite infall.