Redshift evolution of the C1 X-ray luminosity function. The calculation relies on the same assumptions as for the full survey volume luminosity function of Fig. 14, but the sample is split into three redshift bins containing approximately the same number counts of clusters. The dashed lines show, for the same redshift bins, the luminosity function expected in the WMAP9 cosmology from our scaling relation model (M_500,WL − T_{300 kpc} from XXL Paper IV and ). For better visualisation, the bottom panel shows the same information in the form of a residual plot with respect to the WMAP9 expectation at low redshift. A significant negative evolution is visible at z ≥ 0.43.