This talk has been cancelled, and will be postponed until the Spring semester due to it coinsiding with the Decadal Survey on Astronomy and Astrophysics 2020 webinar.
Dynamical resonances are central to the evolution of spiral galaxies after they have been assembled. These resonances rearrange orbital angular momentum and energy in the disk and by doing so evolve disk kinematics, chemical distributions, and morphology. Key to our understanding of this secular evolution is how transient spiral arms cause stars to migrate large radial distances from their birth radii. Most sorts of radial migration are associated with increased orbital eccentricities and thus kinematic heating of the disk. However, a particularly important type of radial migration, called churning or cold torquing, can change the sizes of stellar orbits in the disk without significantly altering their eccentricities. The relative importance of cold or heating radial migration significantly impacts how disks evolve. In this talk, I will demystify the physics that governs various forms of radial migration and discuss their observational signatures. I will then present scaling relations for the efficiency of cold torquing. Finally, I will argue that in some limits cold torquing can, in fact, kinematically heat the disk and why this is significant. First steps have been taken, but there is an ongoing need to further develop the theoretical framework for this and other resonant processes in spiral galaxies, in order to interpret data from high resolution simulations and large, high precision observational surveys of the Milky Way.
