Relation between SFR and D_n(4000) for our sample of star-forming galaxies. Blue, green, red, cyan, magenta, and yellow solid lines represent the running median for bins of 2000 objects in six O/H bins. Black dash-dotted lines show the fit to the running median for bins of 1000 objects in six log(M_⋆/M_⊙), bins, from low stellar mass (8.5, lower part of the figure) to high stellar mass (11.5, higher part of the figure).