BPT emission line diagrams. Each point corresponds to a Voronoi bin, and is colour-coded as located in an H II region (pink) or in the DIG (green). The contours overplotted on the data correspond to iso-proportions of the density, with a probability mass ≤0.25, 0.5, 0.75 and 1. The data are compared to the extreme starburst line from Kewley et al. (2001, black dashed line), the fast shock models from Allen et al. (2008, black grid), and slow shock models from Rich et al. (2011, blue grid).