Groups of Galaxies in the Northern CfA Redshift Survey

We use a friends-of-friends algorithm to identify loose groups from the northern CfA2 survey covering the region 8h≤α1950≤17h and 8.5°≤δ1950≤rr.5°. There are 406 groups; 149 of these contains five or more members within the survey. Geometric simulations guide our choice of the selection parameters; δp/p=80 is the limiting density contrast and V0 350 km s-1 is the fiducial velocity linking parameter. The geometric simulations are particularly important for evaluating the impact of large-scale structure (e.g., the Great Wall) on group selection. The physical parameters of this large sample are coincident with our earlier results 126 groups in Ramella et al. ApJ, 344, 522 (1989): the median velocity dispersion in 192 (156; 229) km s-1 and the median blue log(M/L) is 2.38 (2.20; 2.52). The mass-to-light ratio M/L) is in units of Msun/Lsunfor an assumed Hubble constant, H0=100 km/s/Mpc. The numbers in parentheses are 99% confidence limits. This group catalog provides a substantially larger sample for statistical studies than has been previously available. For example, it provides a more substantial sample for estimation of the distribution of group velocity dispersions and of the group-group correlation function.