Comparison of mission line ratio [N II]/Hα and velocity dispersion. Lower panel: Emission line ratio [N II]/Hα versus the velocity dispersion for individual spaxels. Points are colour-coded based on the function Q described in Equation (1), which combines [N II]/Hα and velocity dispersion. Black curves show shock models derived with MAPPINGS V (see text). Upper panel: Map colour-coded as in the lower panel, showing the region with high [N II]/Hα and high velocity dispersion.