Representative mixing curves for all spaxels classified as “composite” based on their line ratios. The mixing curves are shown in the [N ii]/Hα versus [O iii]/Hβ diagnostic diagram. The observed emission-line ratios are colour-coded based on their de-projected distance from the nucleus. The distance ranges corresponding to the different colours are indicated in the plot. For clarity, only two representative mixing curves are shown. The anchor point for AGN ionisation is defined by log U = −1.1 for the best-fitting model given in Table 2. The two anchor points for photoionisation in H ii regions are defined by log U = −2.75 and log U = −3.5 for an oxygen abundance of 12 + log (O/H) = 9.24.