Identifying groups and clusters in the 2dFGRS

The way in which galaxy properties are influenced by environment is an important constraint on models of galaxy formation. Using the complete2dF Galaxy Redshift Survey (2dFGRS, see Colless et al., 2001),containing over 225,000 galaxy redshifts, we construct the largest and most uniform group catalogue to date. Here we present tests of our methodology, which is underpinned by mock 2dFGRS catalogues made from a combination of high resolution N-body simulations and the Cole et al. semi-analytic model of galaxy formation. Some basic characteristics of the 2dFGRS group catalogue are given. This revised version was published online in July 2006 with corrections to the Cover Date.