vs. M_BH for the CDF-S ‘robust’ sample (filled circles) for the two different timescales discussed in the text. The solid lines show the linear fit to the data. Open diamonds show the best-fit model-predicted variance computed by taking into account the rest-frame T_rest, and Δt_min, rest of each source. The dashed lines mark the best fit to the model predictions (see Sect. 6 for details). The dotted curves represent the model trends for the sources at z = 0.5 (top one) and z = 2.0 (bottom one), which is the approximate redshift range of the CDF-S sample (see Fig. 2).