Radial migration in numerical simulations of Milky Way-sized galaxies
  We show that in N-body simulations of isolated spiral discs, spiral arms
appear to transient, recurring features that co-rotate with the stellar disc
stars at all radii. As a consequence, stars around the spiral arm continually
feel a tangential force from the spiral and gain/lose angular momentum at all
radii where spiral structure exists, without gaining significant amounts of
random energy. We demonstrate that the ubiquitous radial migration in these
simulations can be seen as outward (inward) systematic streaming motions along
the trailing (leading) side of the spiral arms. We characterise these spiral
induced peculiar motions and compare with those of the Milky Way obtained from
APOGEE red clump data. We find that transient, co-rotating spiral arms are
consistent with the data, in contrast with density wave-like spirals which are
qualitatively inconsistent. In addition, we show that, in our simulations,
radial migration does not change the radial metallicity gradient significantly,
and broadens the metallicity distribution function at all radii.
