Subhalos switching host halo affiliation in the Local Group and a possible origin of the Milky Way's satellites

Abstract

In the currently most probable model of the formation of structure in the universe, clumps of dark matter, called halos, form from local concentrations of matter in the early universe and merge to form larger structures, such as galaxy-sized or galaxy cluster-sized halos. Inside these halos, galaxies can form. Smaller halos that have entered a larger halo are called subhalos and can host satellite galaxies. The nearby spiral galaxy Andromeda (M31) could have been the result of a major merger in the past. We see the M31's stellar disk edge-on. This disk determines the plain of the possible major merger and material could have been liberated by this merger and ejected toward the Milky Way (MW). Many satellite galaxies of the MW lie in one single plane through the center of our galaxy, which could be explained by the in fall of a group of satellites (possibly originating from M31). We have used the Cosmogrid cosmological Λ cold dark matter computer simulation to find 47 instances of pairs of halos that resemble the Local Group (LG; consisting of the MW's and M31's halos and their environment) and searched for subhalos contained in either the MW or M31 at the present time (the latest simulation output) that have been a subhalo of the other halo at an earlier time. We call such a subhalo a renegade. It is found that most (27 out of all 47) LG-like pairs do not exhibit a single renegade and those that do contain a renegade population that accounts for up to 7.25 % of the total subhalo population. Renegade subhalos have on average a higher velocity than other subhalos, but the distribution in mass for renegades and all subhalos do not differ much. Due to this higher velocity, most renegades are not bound to the halo they are contained in.