Evolution of galactic discs: multiple patterns, radial migration, and disc outskirts

This paper aims to investigate the evolution of galactic discs in N-body tree-SPH simulations. The authors find that discs, initially truncated at three scale lengths, can triple their radial extent, solely driven by secular evolution. Both Type I and Type II observed disc surface brightness profiles can be explained by the findings. The authors suggest that the naturally occurring larger resonance widths at galactic radii beyond four scale-lengths may have profound consequences on the formation and location of breaks in disc density profiles, provided spirals are present at such large distances. The authors propose that observations of Type III surface brightness profiles, combined with an up-turn in the stellar velocity dispersions beyond the disc break, could be a signature of ongoing gas-accretion. The results of this study suggest that disc outskirts comprised of stars migrated from the inner disc would have relatively large radial velocity dispersions, and significant thickness when seen edge-on.