Non-parametric velocity W80 estimator as a function of [O III] luminosity. Black and green/black symbols refer to the same X-ray/SDSS sources shown in Fig 8; grey circles and pink squares shows type 2 AGNs from Yuan et al. (2016) and Reyes et al. (2008). Large symbols represent median velocities in bins of luminosity for the X-ray/SDSS sample (red/yellow) and for all sources in the figure (blue/cyan); bars indicate semi-interquartile ranges. Yuan et al. and Reyes et al. luminosities have been recomputed consistently with the cosmological parameters shown in the Introduction.