The redshift–space two–point correlation function of galaxy groups in the CfA2 and SSRS2 surveys

We measure the two–point redshift–space correlation function of loose groups of galaxies, ξGG(s) , for the combined CfA2 and SSRS2 surveys. Our combined group catalog constitutes the largest homogeneous sample available (885 groups). We compare ξGG(s) with the correlation function of galaxies, ξgg(s) , in the same volume. We find that groups are significantly more clustered than galaxies: < ξGG/ξgg > =1.64± 0.16. A similar result holds when we analyze a volume–limited sample (distance limit 78 h Mpc) of 139 groups. For these groups, with median velocity dispersion σv ∼ 200 km s −1 and mean group separation d ∼ 16 h Mpc, we find that the correlation length is s0 = 8±1 h −1 Mpc, which is significantly smaller than that found for rich clusters. We conclude that clustering properties of loose groups of galaxies are intermediate between galaxies and rich clusters. Moreover, we find evidence that group clustering depends on physical properties of groups: correlation strengthens for increasing σv.