Rotational velocities for the high- and low-extinction PNe are shown in blue and red, respectively. The black line shows the H I rotation velocity from Chemin et al. (2009). The co-rotation radius (black dotted line) and outer Lindblad resonance (OLR; black dashed line) of the M 31 bar are as found by the models of Blaña et al. (2018). The grey shaded region is possibly influenced by different dynamical heating events and is not discussed here.