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abstract
N-body simulations of galaxy pairs on parabolic orbits are conducted in order to quantify the effect of dynamical friction. The effect of varying the extent and mass of the dark matter halos and the distance of closest approach are explored. More massive simulated galaxies achieve a larger maximum distance after the first encounter despite the increased dynamical friction caused by the more extended dark matter halos. Projected separation and radial velocity histograms are generated by ``observing'' the simulation results at various times and from various orientations. These histograms are compared with observations of galaxy pairs (Charlton \& Salpeter 1991, ApJ, 375, 517; Chengalur, Salpeter, \& Terzian 1993, ApJ, 419, 30) in order to place constraints on the various parameters. Dark matter halos that extend at least 25 times farther than the luminous galaxy are necessary to match the observed histograms. It is difficult to reconcile the small radial velocity differences that have been observed (median of $\sim$ 30 km/s, Chengalur et al. 1993) with the simulations when we sample all parts of the orbits equally. This suggests that dynamical friction is not sufficient to produce small velocity differences, and that it is likely that many pairs have just recently reached ``turnabout'' from the Hubble flow.
