Left: oxygen abundance 12 + log(O/H) as a function of the radius (in units of R_e), colour-coded as a function of the stellar mass log(M_⋆/M_⊙), as reported in the legend. The shaded regions represent the upper and lower errors of the radial gradients, which were obtained by calculating the 16th and 84th of the distribution in each stellar mass bin taking into account the number of galaxies lying in the bin. Right: metallicity gradient estimated in the radial range 0.5−2 R_e from a linear fit of the corresponding radial profiles in different mass bins as a function of stellar mass (in red). The metallicity gradients estimated with M08 and PP04 calibrations are reported in green and blue, respectively, while those taken by Belfiore et al. (2017) are reported in lime green and cyan.