Radial mixing in the outer Milky Way disc caused by an orbiting satellite

Abstract

Using test particle simulations, we examine the structure of the outer Galactic disc as it is perturbed by a satellite in a tight eccentric orbit about the Galaxy. A satellite of mass a few times 109 M⊙ can heat the outer Galactic disc, excite spiral structure and a warp and induce streams in the velocity distribution. We examine particle eccentricity versus the change in mean radius between initial and current orbits. Correlations between these quantities are reduced after a few satellite pericentre passages. Stars born in the outer galaxy can be moved in radius from their birth positions and be placed in low eccentricity orbits inside their birth radii. We propose that mergers and perturbations from satellite galaxies and subhaloes can induce radial mixing in the stellar metallicity distribution.