ON THE PAIRWISE VELOCITY DISPERSION OF GALAXIES

Previous statistical results have shown that the pairwise velocity dis persion sigma(g)(r(p)) of galaxies at small separations (r(p) almost-e qual-to 1 h-1 Mpc) is about 300 km s-1. This value is significantly lo wer than the predictions of currently favoured models of structure for mation, unless a large pairwise velocity bias exists between galaxies and the underlying mass. Using various samples of galaxies (CfA, SSRS, IRAS, CfA slice, samples containing ellipticals or spirals), we show that the results of sigma(g)(r(p)) are sensitive to sampling effects, such as the inclusion of dominating clusters, and the correction of th e Virgocentric infall. The value of sigma(g)(r(p) = 1 h-1 Mpc) is as h igh as approximately 1000 km s-1 for the CfA slice including Coma, and as low as approximately 300 km s-1 for the spiral sample and for the CfA sample with a correction of the Virgocentric infall. The values of sigma(g) that we obtain are consistent with the high values predicted by currently favoured models of structure formation, which suggests t hat a high pairwise velocity bias between galaxies and mass is not req uired by present data.