Simulations of merging galaxies

A series is presented of N-body simulations of the merging of pairs of galaxies. A galaxy is represented by a spherical, centrally condensed cluster of 250 softened particles, and is put into a bound or parabolic orbit with either a single point mass or a second 'galaxy'. Tidal effects cause rapid merging whenever two 'galaxies' overlap significantly at closest approach, and the final coalesced object has a higher central concentration and a more extensive envelope than did its progenitors. Radial population gradients are severely weakened by the merging process. It seems that mergers can produce objects similar to observed elliptical galaxies with fairly flat rotation curves and low peak rotation velocities, but they cannot easily explain the outer halos of cD galaxies. Mergers will be exceedingly common if all galaxies have dark isothermal halos. One of the models is used to test the standard dynamical friction formula: theory and experiment agree quite well. (author)