The Effects of Radial Migration on the Outskirts of Disc Galaxies

Abstract

Since the discovery of radial migration a galaxy can no longer be considered to be a collection of annuli evolving in isolation. Previous works have considered the implications of migration on properties of disc galaxies, but most of these efforts concentrate on the Solar neighbourhood, where observational comparisons are at their best. Only a small number of studies have investigated the effect on the outer regions of galaxies. Using N-body+SPH simulations, I consider the effect of radial migration on the outskirts of disc galaxies. I demonstrate that when falling through a gas rich cluster environment, a galaxy can evolve from a type II profile to a type I profile with little increase in the radial velocity dispersions. Instead the cluster environment induces more spirals when compared to the same galaxy evolving in isolation, driving radial migration of stars into the outer disc and explaining the relative abundance of type I galaxies in cluster environments. I demonstrate that during the transformations of the profiles the galaxy evolves from a spiral to a lenticular galaxy and becomes redder. This significantly alters the position of the galaxy in the colour-mass plane, transitioning from the blue sequence to the green valley. Furthermore, these changes occur rapidly after the onset of ram pressure stripping. Finally I consider the effects of migration in disc galaxies with strong warps. I find that the warp remains isolated from the mixing effect of migration and thus forms a tight relation between age and metallicity. Stars forming in the warp settle into the disc, where they migrate across all radii, imprinting the warp AMR over the flattened, broadened disc AMR.