Diagnostic diagrams used to provide our BPT classification (see Sect. 4.2). Top and middle panels: main-ELG [N II] and [S II] BPT diagrams. Galaxies are color-coded by their sSFR; here we show only 60 percent, randomly sampled, of each population to avoid saturation. We overplot the Kewley et al. (2001), Kauffmann et al. (2003a) and Kewley et al. (2006) demarcation lines (black solid, dot-dashed, and thick dotted lines, respectively) separating the SF, AGN, LINER, and Seyfert contributions (see Sect. 4.2). Ambiguous objects are represented as stars. Bottom: Seyfert, passive, and ambiguous components of the main-ELG sample represented in the WHAN diagram, together with the EW cuts we use to select them: the EW = 6 Å limit (dot-dashed line) separating Seyferts from LINERs, and the EW = 0.5 Å cut (Cid Fernandes et al. 2011; solid) to isolate passive ELGs from the rest.