Stellar Migration in Galaxy Disks Using the Chirikov Diffusion Rate

We are reexamining the problem of stellar migration in disk galaxies from a diffusion perspective. We use for the first time the formulation of the diffusion rates introduced by Chirikov, applied to both energy, E, and angular momentum, Lz, in self-consistent N-body experiments. We limit our study to the evolution of stellar disks well after the formation of the bar, in a regime of adiabatic evolution. We show that distribution functions of Chirikov diffusion rates have similar shapes, regardless of the simulations, but different slopes for energy and angular momentum. Distribution functions of derived diffusion timescales, TD, also have the same form for all simulations, but are different for TD(E) and TD(Lz). Diffusion timescales are strongly dependent on Lz. TD(E) 1 Gyr in a Lz range roughly delimited by the set of stellar bar resonances (between the ultraharmonic resonance and the outer Lindblad resonance). Only particles with low Lz have TD(Lz) 10 Gyr, i.e., the simulation length. In terms of mass fraction, 35%–42% turn out to diffuse energy in a characteristic timescale shorter than 10 Gyr, i.e., simulations length, while 60%–64% undergo the diffusion of the angular momentum on the same timescale. Both the diffusion of Lz and E are important to grasp the full characterization of the radial migration process, and we show that depending on the spatial region considered, one or the other diffusion dominates.