BPT diagram of 26 blue (SF+LINER) and 31 red (SF+LINER) Lockman Hole galaxies with SDSS spectra available in the highest redshift bin. Arrows mark the limits for galaxies for which only three optical lines are measured above S/N > 2 (in the other galaxies all four lines have S/N > 2). The vertical and horizontal lines represent the conventional separation for LINERs (i.e. [O iii]/Hβ < 3 and [N ii]/Hα > 0.6) and Seyfert galaxies (i.e. [O iii]/Hβ > 3 and [N ii]/Hα > 0.6). In this work we adopt the demarcation by Kauffmann et al. (2003, dashed line) to separate star-forming galaxies from LINERs. The dotted line indicates the more stringent demarcation to identify AGN, proposed by Kewley et al. (2001). The radio subsample is marked by circles (31 sources). This figure excludes the inactive galaxies, see Sect. 5.2 for more detail.