“Dynamical Chaos near Corotation: Limits on cold radial migration”
After an initial epoch of assembly, spiral galaxies like the Milky Way evolve primarily under the influence of slow, internal processes. This secular evolution rearranges the orbital angular momentum and energy of the disk, thus altering its kinematics, morphology and chemical distribution. Dynamical resonances with spiral arms cause stars to migrate large radial distances from their birth radii. Most radial migration is associated with kinematic heating. However, transient spiral arms drive a particularly important process, called cold torquing, that can change the orbital sizes of a substantial fraction of disk stars over the lifetime of the disk without kinematically heating it. The relative importance of cold or heating radial migration significantly impacts how disks evolve. High resolution simulations of spiral galaxies, as well as large, high precision observational surveys of the Milky Way disk, stress a critical need to further develop a theoretical framework for interpretation of these results. In this talk, I will quickly demystify the physics that governs radial migration and cold torquing and present scaling relations that constrain its efficiency. I will then argue that in some limits cold torquing can, in fact, kinematically heat the disk. First steps have been taken, but there is an ongoing need to better understand the nature of transient spiral structure and the role cold torquing has played in the evolution of the Milky Way.