identify only systems where inter-galaxy separations are comparable with their physical size.

The line-of-sight velocity difference between galaxies in a gravitationally bound system is a measure of their relative peculiar velocity. The median radial velocity dispersion in HCG’s is only $\sim$ 200 km s$^{-1}$ (Hickson et al.  1992). We choose the value $V_{0}$ = 1000  km s$^{-1}$, which is large enough to include most physically associated galaxies in compact groups. This value of $V_{0}$ is, however, not so large that the resulting “groups” accidentally span voids in the galaxy distribution (Geller & Huchra 1989). This value is consonant with Hickson’s procedure of rejecting galaxies with velocities different from the median group velocity by $\geq$ 1000 km s$^{-1}$ (Hickson et al.  1992).

The parameter $D_{0}$ directly limits the physical extent of our compact groups. We use $D_{0}$ to match our sample to the HCG’s. As a measure of the spatial extent of HCG’s, we use the distribution of all projected separations, $\Delta D$, among Hickson group members. We compare the distribution to the distribution of all projected separations in compact group catalogs extracted from the CfAnorth catalog. We apply the friends-of-friends algorithm to construct catalogs of compact group candidates at several 