Stellar mass vs. difference in log units of the velocity dispersion measured from spectra and calculated through the virial equation. Upper panel: difference before the correction of the stellar mass. Lower panel: indicates that once the mass is corrected for the contribution of DM the two quantities are in good agreement (see text). Black dots are normal ETGs, green dots the faint ETGs measured by Bettoni et al. (2016), blue dots are galaxy clusters.