log(L_bol)–z plane for the sources surviving the binning selection and the colour cut (see text for details). The final sample spans roughly 2.5 decades in bolometric luminosity and covers up to z ∼ 2.9. The data are randomly coloured if the bin contains more than 30 objects to make the binning clearer. The black diamonds mark the average z and log(L_bol) values. The legend reports the fraction of sources having data in the labelled band. Since the sample is based on the cross-match between the SDSS and the AllWISE catalogues, all objects have data in the bands covered by these surveys, while only a minority have a full coverage across the several wave bands.