Predicted relation between the velocity dispersion σ and the stellar mass M_* for passive galaxies (see text). The color code represents the logarithm of the fraction of model galaxies with the considered σ for each bin of M_*. The shaded band shows the relation for early-type galaxies selected on the basis of morphological indicators after Hyde & Bernardi (2009). The dashed black and red lines show the average relation derived by Zahid et al. (2016) for passive SDSS galaxies and for the Smithsonian Hectospec Lensing Survey (SHELS) sample, selected on the basis of spectral properties (D_n4000 > 1.5, where D_n4000 is the flux ratio of two spectral windows adjacent to the 4000 Å break (see Balogh et al. 1999).