Comparison of D_n4000 measurements of CIGALE with the input (data) values for the AGNs (top panel) and the galaxies in the reference catalogue (bottom panel). The index is not included as input (data) in the fitting process. In both cases, the algorithm successfully recovers the input value of the index. The dashed lines in the two panels present the best linear fits. In the case of AGNs, the fit is given by the following expression: D_n4000_CIGALE = 0.7903 × D_n4000_data + 0.3236. For the reference sample, a similar equation is found: D_n4000_CIGALE = 0.7567 × D_n4000_data + 0.3230. Solid black lines present the 1:1 relation.