  Using numerical simulation, we study the response of a disk galaxy to a
merger involving a low-mass satellite companion. During a prograde satellite
accretion, the disk galaxy forms a strong bar in response to the perturbation
of the companion. After the accretion event is over, the bar buckles vertically
due to a bending instability, sending disk material well out of the disk plane.
The material forms into an X-shaped feature when seen edge-on, morphologically
similar to X-structures observed in several S0/Sa galaxies. The mechanism
described here unites previously suggested accretion and bar instability
hypotheses for forming X-structures into a self-consistent scenario for
merger-induced formation and evolution of S0 galaxies. To complement these
models, we also present observations of the peculiar S0 galaxy Hickson 87a. The
thick disk, isophotal warping, and strong X-structure described in the merger
model are all evident in Hickson 87a, suggesting this galaxy may be an
excellent example of such merger-induced galaxy evolution.
