Groups of Galaxies in the Northern CfA Redshift Survey

Abstract

We use a friends-of-friends algorithm to identify loose groups from the northern CfA2 survey covering the region 8 h ^a 1950 ^17 h and 8.5°^^950^44.5°. There are 406 groups; 149 of these contains five or more members within the survey. Geometric simulations guide our choice of the selection parameters; Sp/p=80 is the limiting density contrast and V 0 =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~ l and the median blue log(^#/L) is 2.38 (2.20; 2.52). The mass-to-light ratio {^SIL) is in units of for an assumed Hubble constant, // 0 =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. © 1997 American Astronomical Society. [80004-6256(97)03702-3]