BPT diagrams. Comparison of the observed line ratios with the model predictions. The gray dots (filament values) and the stars (nucleus values) represent the data from Mcdonald et al. (2012). The size of the dots decreases with increasing distance of the corresponding object from the nuclei. The solid black line is the upper limit for HII regions by Kewley et al. (2001) and the dashed black line is the lower limit for AGNs by Kauffmann et al. (2003). The predicted cumulative line ratios from the models are overlaid. The gray lines correspond to a single value of metallicity and different values of turbulence (the velocity value is written on the left and reproduced with different colours); from left to right the velocity is constant and the metallicity increases (from 0.3 to 1 Z_⊙). The G_X is fixed to 100. Left column: cumulative emission of [O III]λ 5007 Å/Hβ vs. [N II]λ 6583 Å/Hα; central column: [O III]λ 5007 Å/Hβ vs. [S II]/Hα; right column: [O III]λ 5007 Å/Hβ vs. [O I]/Hα. Top row: cumulative emission at A_V = 0.001 mag; second row: cumulative emission at A_V = 0.1 mag; third row: cumulative emission at A_V = 1 mag; bottom row: cumulative emission at A_V = 5 mag.