Stellar Migration by Short Lived Density Peaks Arising from Interference
  of Spiral Density Waves in an N-body Simulation
  We identify migrating stars in an N-body simulation of a Milky-Way-like disk.
Outward migration can occur when a star in a low eccentricity orbit lags a
short-lived local spiral arm density peak. We interpret short lived local
density peaks, that appear and fade on approximately an orbital period, as
arising from positive interference between spiral density wave patterns. Stars
near such a peak can migrate over a significant distance in galactocentric
radius during the peak lifetime, providing that the peak is sufficiently dense.
Using a Gaussian bar model for the potential perturbation associated with a
narrow transient spiral feature, estimates of the migration rate, angular
offset between particle and spiral feature, and maximum eccentricity for
migrators roughly agrees with the values measured in our simulation. When
multiple spiral density waves are present, local density peaks can appear and
disappear on timescales faster than the timescale estimated for growth and
decay of individual waves and the peak surface density can be larger than for
any individual wave. Consequently, migration induced by transient density peaks
may be more pervasive than that mediated by the growth and decay of individual
patterns and occurring at their corotation resonance. We discuss interpretation
of transient-like behavior in terms of interfering patterns, including
estimating a coherence time for features that appear due to constructive
interference, their effective angular rotation rates and the speed and
direction that a density maximum would move across a galaxy inducing a
localized and traveling burst of star formation.
