The consequences of minor mergers for disk galaxies

We perform self-consistent stellar dynamical simulations of satellite galaxy accretion by a large disk galaxy. Our fiducial model begins with a satellite in a prograde, circular orbit inclined 30;During the prograde satellite accretion, the disk forms a strong bar. After the accretion event is over, the bar buckles vertically, 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. This mechanism unites accretion and bar instability hypotheses for forming X structures into a self-consistent scenario for merger-induced formation and evolution of S0 galaxies. We also present observations of the peculiar S0 galaxy Hickson 87a. The thick disk, isophotal warping, and strong X structure of the merger model are all evident in Hickson 87a: this galaxy may be an excellent example of such merger-induced galaxy evolution.;The simulations are used to test the analytic model of Toth and Ostriker which, in its simplest form, is found not to work well. A generalization of their model, featuring mass loss from the satellite, an arbitrary rotation curve, and explicit inclination dependence, is a considerable improvement but still does not fit the outer disk. Possible future extensions are discussed.