Left panel. Relation between size and stellar mass for all galaxies in the two simulations. Dots and diamonds are the median values in bins of halo mass, and the shaded areas indicate the 16% and 84% quantiles. Single dots are for individual galaxies, in bins containing fewer than ten galaxies. The vertical lines mark the minimum masses considered for the two simulations in the computation of the analytic fits. Middle panel. Relation between stellar mass, M_★, and halo mass, M₂₀₀, for all central galaxies in the two simulations. Symbols are as in the left panel. The vertical lines mark the lower halo mass limit of the samples extracted from the two simulations and employed in the computation of the R₁ − R₂₀₀ relation. Right panel. Same as the middle panel, but for the R₁ − M₂₀₀ relation.