Nearby groups of galaxies. I. The NGC 1023 group

New H I radial velocities of galaxies have been acquired in a large region around NGC 023. Hierarchical clustering techniques have been developed as a means to describe the clustering properties of galaxies. The most satisfactory method merges entities sequentially on the basis of a maximization of the gravitational force. Plotted as a function of the luminous density, the hierarchy provides a direct estimate of the mass-to-light ratio that is required if any given level is to be gravitationally bound. The hierarchy can be used as a guide toward the delineation of groups that have physical significance. Arguments based on crossing times and 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. It is argued that the superposed galaxy UGC 2080=IC 239 is, in fact, located in the background. The mass derived by a dynamical anaylsis is consistent, within the uncertainties, with the sum of the masses associated with the disks of the individual galaxies. The derived virial--mass-to-light ratio is 19(+28, -14) M/sub sun//L/sub sun/ (H0=75 km s-1 Mcp-1). However, this mass might be underesimated since, according to the gravitational clustering theory, the group is near its maximum extent today and one expects most of the binding energy to be in the form of potential energy. A means of establishign a lower limit for the cosmological dentisy parameter is discussed There are two small groups each roughly 5 Mpc from the NGC 1023 group, and their integrity has not been jeopardized by the tidal shear created by the NGC 1023 group since, at least, the epoch zapprox.3