Exponential Galaxy Disks from Stellar Scattering
  Stellar scattering off of orbiting or transient clumps is shown to lead to
the formation of exponential profiles in both surface density and velocity
dispersion in a two-dimensional non-self gravitating stellar disk with a fixed
halo potential. The exponential forms for both nearly-flat rotation curves and
near-solid body rotation curves. The exponential does not depend on initial
conditions, spiral arms, bars, viscosity, star formation, or strong shear.
After a rapid initial development, the exponential saturates to an
approximately fixed scale length. The inner exponential in a two-component
profile has a break radius comparable to the initial disk radius; the outer
exponential is primarily scattered stars.
