Double galaxies. II - Data analysis and a galaxian mass /M/L/ determination

Various aspects of a sample of 279 double galaxies over a wide range of separations are investigated. The distribution of spatial separations is determined from a previously derived true angular-separation distribution, projected linear separations, and radial-velocity differences are calculated, and the distributions of these are presented. A statistical method is developed for estimating an average galactic mass based on the orbital data for a given sample of binary galaxies. Average masses and M/L ratios are determined for galaxy pairs grouped according to projected separations. The variation of these two quantities as a function of pair separation is considered relative to the massive-halo hypothesis, and an alternative explanation for the functional dependence is proposed. Mass estimates based on the orbital parameters are then compared with an average mass derived from the global H I properties of the individual galaxies. It is found that the data apparently eliminate an extended massive-halo component.