Thick-disk evolution induced by the growth of an embedded thin disk
  We perform collisionless N-body simulations to investigate the evolution of
the structural and kinematical properties of simulated thick disks induced by
the growth of an embedded thin disk. The thick disks used in the present study
originate from cosmologically-common 5:1 encounters between initially-thin
primary disk galaxies and infalling satellites. The growing thin disks are
modeled as static gravitational potentials and we explore a variety of
growing-disk parameters that are likely to influence the response of thick
disks. We find that the final thick-disk properties depend strongly on the
total mass and radial scale-length of the growing thin disk, and much less
sensitively on its growth timescale and vertical scale-height as well as the
initial sense of thick-disk rotation. Overall, the growth of an embedded thin
disk can cause a substantial contraction in both the radial and vertical
direction, resulting in a significant decrease in the scale-lengths and
scale-heights of thick disks. Kinematically, a growing thin disk can induce a
notable increase in the mean rotation and velocity dispersions of thick-disk
stars. We conclude that the reformation of a thin disk via gas accretion may
play a significant role in setting the structure and kinematics of thick disks,
and thus it is an important ingredient in models of thick-disk formation.
