Same line ratios as in Fig. 3 plotted against Σ_star (left), ⟨I_CO⟩ (middle), and Σ_SFR (right) on a pixel-by-pixel basis (grey points). All panels have the same vertical and horizontal span in dex for an easier comparison. For each line ratio and galaxy, the colour squares and vertical bars represent the mean and the ±1σ standard deviation within bins of the x-axis parameter. The squares are white-filled where the mean value does not necessarily represent the whole galaxy (Sect. 6).