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 hybrid simulation of a Milky-Way-like disk. Outward migration can occur when a star in a low eccentricity orbit lags a shortlived 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 that are longer lived. We nd that stars near such a peak can migrate over a signicant distance in galactocentric radius during the peak lifetime, providing that the peak is suciently dense. We propose that short lived density peaks, caused by interference between spiral density waves, can induce radial migration even when there are no spiral density waves that are strong near their corotation resonance. Using a Gaussian bar model for the potential perturbation associated with a narrow transient spiral feature, estimates of the migration rate, angular oset 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 eective 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.