Velocity anisotropy area (A_β) and area difference (ΔA_β) for the N2M model. Panels a and b show the velocity anisotropy for the two populations (red upper triangles, PO1P, and downwards blue triangles, PO2P) in the N2M model at 4 Gyr and 12 Gyr, respectively. The hatched regions represent the respective anisotropy area for each population from the best-fit velocity dispersion and anisotropy parameterisation (see main text). Panel c shows the evolution of the anisotropy areas for the two populations over time; as the 2P becomes less radially anisotropic, the 1P becomes tangentially anisotropic and keeps a constant difference with the 2P, as shown in panel d, where we show the evolution of the anisotropy area difference. The vertical lines in panels c and d represent the times for which we show the velocity anisotropy profiles in panels a and b.