Radial Migration in Disk Galaxies I: Transient Spiral Structure and
  Dynamics
  We seek to understand the origin of radial migration in spiral galaxies by
analyzing in detail the structure and evolution of an idealized, isolated
galactic disk. To understand the redistribution of stars, we characterize the
time-evolution of properties of spirals that spontaneously form in the disk.
Our models unambiguously show that in such disks, single spirals are unlikely,
but that a number of transient patterns may coexist in the disk. However, we
also show that while spirals are transient in amplitude, at any given time the
disk favors patterns of certain pattern speeds. Using several runs with
different numerical parameters we show that the properties of spirals that
occur spontaneously in the disk do not sensitively depend on resolution. The
existence of multiple transient patterns has large implications for the orbits
of stars in the disk, and we therefore examine the resonant scattering
mechanisms that profoundly alter angular momenta of individual stars. We
confirm that the corotation scattering mechanism described by Sellwood & Binney
(2002) is responsible for the largest angular momentum changes in our
simulations.
