Fitting functions for the Σ_⋆(R_edge)−M_⋆ relation (grey points). The mean Σ_⋆(R_edge) is computed in steps of 0.1 dex over the plotted stellar mass range (cyan squares). The best fits (purple lines) are the two linear relations in Eqs. 3 and 4, split at 10^10.5 M_⊙ (vertical black dashed line). For contrast, we also show a single linear fit (pink dot-dashed line) and polynomial fit of degree two for the full sample (orange dashed line).