X-ray luminosity at 2 keV as a function of the total integrated C IV line luminosity. Green squares highlight the sources used in the MCMC regression line analysis. Black circles describe a lower-redshift and lower-luminosity SDSS-XMM sample with a robust measurement of the integrated C IV line luminosity (Signorini et al., in prep.). The dotted line represents three times the intrinsic dispersion on the relation, ∼0.5 dex.