Comparison of the distributions of D_n4000 and H_δ (in Å) for galaxies in the reference catalogue and AGN, when excluding systems as quiescent systems based on D_n4000 and H_δ (see text for more details). Sources in the reference catalogue tend to have younger stellar population (smaller D_n4000) and are more likely to have undergone a recent star formation burst (higher H_δ), compared to AGN.