Radial Mixing in Galactic Disks: The Effects of Disk Structure and
  Satellite Bombardment
  We use a suite of numerical simulations to investigate the mechanisms and
effects of radial migration of stars in disk galaxies like the Milky Way (MW).
An isolated, collisionless stellar disk with a MW-like scale-height shows only
the radial "blurring" expected from epicyclic orbits. Reducing the disk
thickness or adding gas to the disk substantially increases the level of radial
migration, induced by interaction with transient spiral arms and/or a central
bar. We also examine collisionless disks subjected to gravitational
perturbations from a cosmologically motivated satellite accretion history. In
the perturbed disk that best reproduces the observed properties of the MW, 20%
of stars that end up in the solar annulus 7 kpc < R < 9 kpc started at R < 6
kpc, and 7% started at R > 10 kpc. This level of migration would add
considerable dispersion to the age-metallicity relation of solar neighborhood
stars. In the isolated disk models, the probability of migration traces the
disk's radial mass profile, but in perturbed disks migration occurs
preferentially at large radii, where the disk is more weakly bound. The orbital
dynamics of migrating particles are also different in isolated and perturbed
disks: satellite perturbations drive particles to lower angular momentum for a
given change in radius. Thus, satellite perturbations appear to be a distinct
mechanism for inducing radial migration, which can operate in concert with
migration induced by bars and spiral structure. We investigate correlations
between changes in radius and changes in orbital circularity or vertical
energy, identifying signatures that might be used to test models and
distinguish radial migration mechanisms in chemo-dynamical surveys of the MW
disk.
