Black hole mass, M_BH, as a function of M_*. Different symbols correspond to different redshift bins, as indicated in the legend. The p-values obtained by applying a Spearman correlation analysis for the full redshift range (z < 1.9) as well as at low redshift (z < 0.7) and high redshift (0.7 < z < 1.9) are also shown. Measurements are colour-coded based on the N_H of each source.