Nearby groups of galaxies. I. The NGC 1023 group.

With regard to new H I radial velocities of galaxies which have been acquired in a large region around NGC 1023, a hierarchical clustering technique is developed which merges entities sequentially on the basis of a maximization of the gravitational force. The hierarchy provides a direct estimate of the mass-to-light ratio that is required if any given level is to be gravitationally bound. Arguments based on crossing times and the application of the virial theorem lead to the identification of a group of 13 galaxies in the region around NGC 1023 which is almost certainly bound, and it is suggested that the superposed galaxy UGC 2080 = IC 239 is located in the background. The derived virial-mass-to-light ratio is found to be 19 (plus 28, minus 14) solar masses/solar luminosities. Reasons related to the gravitational clustering theory for a possible underestimate of this mass are discussed, along with a means of establishing a lower limit for the cosmological density parameter.