Redshift evolution of the slope of the F_X − F_UV relation in narrow redshift bins (top panel). To perform the regression fit, X-ray and UV fluxes are normalised to 10⁻³¹ and 10⁻²⁷ erg s⁻¹ cm⁻² Hz⁻¹, respectively. The data points are plotted at the average redshift within the interval. Error bars represent the 1σ uncertainty on the mean in each bin. The solid and dashed grey lines are the mean and 1σ uncertainty range on the slope (γ). The red line marks γ = 0.6. The bottom panel shows the dispersion (δ, blue filled circles) along the best fit of the F_X − F_UV relation and the dispersion of the distance distribution (δ_DL ≃ 0.06, square symbols) in each bin. See Section 5.3 for details.