An invited review presented at IAU Symp. 171,
New Light on Galaxy Evolution,
Heidelberg, Germany, June 26-30, 1995.
The bridges and tails of interacting galaxies were elegantly explained when Toomre & Toomre (1972) showed that such features arise from tides acting on disk galaxies. Emboldened by this success, Toomre & Toomre proposed that certain twin-tailed fuzzballs without obvious interaction partners were in fact the merged relics of interacting pairs, and that such relics eventually become elliptical galaxies. Observations of twin-tailed systems found evidence for both their tidal origins and their elliptical destinies (e.g. Schweizer 1986), while self-consistent numerical simulations substantiated theoretical predictions of rapid orbital decay and the elliptical-like outcome of violent relaxation during merging (e.g. Barnes 1988, and references therein). But while our basic picture of merging seems solid, the precise role of this process in galaxy evolution is not so clear. Dynamical studies provide some insight into this issue; at present we can distinguish three levels of reliability in the numerical work: solid results, good bets, and hopeful guesses.
Retrograde 3:1 Merger. This sequence shows the parabolic encounter and subsequent merger of two disk galaxies with mass ratios of 3:1.
A compressed postscript copy of this paper is available. The text will be published in New Light on Galaxy Evolution, eds. R. Bender & R. Davies (Kuluwer).
Last modified: December 12, 1995