The zCOSMOS 20k Group Catalog - Knobel, C; Lilly, S; Iovino, A; Kovac, K; Bschorr, T; Presotto, V; Oesch, P; Kampczyk, P; Carollo, C; Contini, T; Kneib, J; Fevre, O; et al. (Astrophysical Journal, 2012)