D4000n index and sSFR. Top and middle: sSFR from Chang et al. (2015) versus D4000n for the PSS-CSO and the ECS samples. Filled squares signify sSFR data from good model fits (FLAG = 1). The dashed line indicates the boundary between the SF sequence (above) and passive galaxies (below). The dotted line is a power-law approximation of the mean values from Brinchmann et al. (2004, their Fig. 11). The spectral types t_SED from the MBSED fit are colour coded as in Fig. 12. Bottom: Histogram distributions of the D4000n index for the PSS-CSO (blue) and ECS (green) galaxies with S/N > 3.