Procedure to use the model as a secondary distance indicator. Left: grid of constant M_* model curves linking V_c, e and the mean stellar surface density (brightness) within the effective radius, (axis are inverted). Each curve is computed using the fiducial model described in Sect. 3.3, using the EAGLE M_* − M₂₀₀ relation (see the left-hand panel of Fig. 2). Galaxy stellar masses may be interpolated using this grid for all galaxies, regardless of morphological type. All EAGLE galaxies are shown shaded in grey according to stellar mass; circles for early-types, spirals for late types, and squares for the rest. Right: galaxy stellar masses predicted from the location of simulated galaxies in the V_c, e − Σ_e plane on the left as a function of their true stellar mass. Is remarkable the excellent agreement and the rather small scatter around the median trend, shown by the magenta solid line (error bars indicate 25–75 percentile range). Results of the same fiducial model, applied to the TNG dataset are shown by the thick green line (data for individual TNG galaxies not shown, for clarity). The good agreement suggests that the location of a galaxy in the V_c, e − Σ_e plane can be effectively used as a powerful secondary distance indicator applicable to galaxies of all morphological types.