The evolution of substructure III: the outskirts of clusters
  We present an investigation of satellite galaxies in the outskirts of galaxy clusters taken from a series of high-resolution N-body simulations. We focus on the so-called "backsplash population", i.e. satellite galaxies that once were inside the virial radius of the host but now reside beyond it. We find that this population is significant in number and needs to be appreciated when interpreting the various galaxy morphology environmental relationships and decoupling the degeneracy between nature and nurture. Specifically, we find that approximately half of the galaxies with current clustercentric distance in the interval 1-2 virial radii of the host are backsplash galaxies which once penetrated deep into the cluster potential, with 90% of these entering to within 50% of the virial radius. These galaxies have undergone significant tidal disruption, loosing on average 40% of their mass. This results in a mass function for the backsplash population different to those galaxies infalling for the first time. We further show that these two populations are kinematically distinct and should be observable within existent spectroscopic surveys. 
Stuart P.D. Gill, Alexander Knebe, Brad K. Gibson (Swinburne   University)