Figures adapted from Marini et al. (2025a). Right panel: Completeness (black) and contamination (red) as a function of halo mass for Yang et al. (2005)’s Friends-Of-Friends (FoF) algorithm results applied to the MAGNETICUM mock optical catalog. The shaded region corresponds to the 95th binomial confidence interval. Left panel: Comparison of the halo mass estimated by the Yang et al. (2005) FoF algorithm as a function of the true input mass from MAGNETICUM. Masses are estimated from the total stellar luminosity proxy.