Distributions of the D_n(4000) for all galaxies (SF, composite, and AGN), following the format in Fig. 4. Vertical lines indicate the median values for all the galaxies in each sample, with the respective colour and line style according to the legend. Arrows indicate the median values when separating into young and old stellar populations (blue and red areas, respectively). The corresponding median values and standard deviations are presented in Table 6.