Eke, V., Baugh, C., Cole, S., Frenk, C., & Navarro, J. (2006). Galaxy groups in the 2dF Galaxy Redshift Survey: the number density of groups. Monthly Notices of the Royal Astronomical Society, 370, 1147-1158. https://doi.org/10.1111/j.1365-2966.2006.10568.x