Shock models on the BPT diagrams. Only points with detected [OI] emission are plotted. The blue (resp. red) points lie in (resp. out of) the star formation locus on the [OI]/Hα BPT diagram. The purple dashed line is the ionization model prediction from MAPPINGS V, using a metallicity Z = 0.5 Z_⊙ and log(P/k) = 5.2. The ionization parameter goes from log U = −2 to log U = −3.5, as indicated in the third diagram. The two grids come from the MAPPINGS III model for fast shock, as described in the text, and are drawn for shock only and shock + precursor.