N-body studies of compact groups of galaxies dominated by dark matter

Systems consisting of a few galaxies embedded in a background cluster of smoothly distributed dark matter may evolve significantly over cosmological time-scales as the galaxies spiral to the centre. Virial and other mass estimates using the present galactic positions and velocities yield serious underestimates of the total system mass. N-body models of such systems confirm the qualitative predictions of simplified dynamical theories. However, the evolution in real systems is retarded by the response of the background to the galaxies; thus theories which assume a fixed background generally overestimate evolutionary effects. (author)