Toomre diagram illustrating the six groups extracted from the HC, arranged in descending order of median metallicity, 〈[Fe/H]〉. The vertical dot-dashed line marks the Sun’s velocity at 232.8 km s⁻¹, as estimated by McMillan (2017). Concentric dashed circles represent constant total velocities of 50, 100, 150, and 200 km s⁻¹, centred around the Sun’s velocity in this diagram. Velocities are corrected for the solar motion using {U_⊙, V_⊙, W_⊙} = {8.6±0.9, 13.9±1.0, 7.1±1.0} km s⁻¹, following the values reported by McMillan (2017, Table 2). A consistent range on both axes is maintained to facilitate comparison across groups and highlight outliers, particularly those with lower metallicities. The colour scheme corresponds to that used in previous figures: stars with combined velocities exceeding 100 km s⁻¹ are designated as outliers and marked in magenta. Subplot labels indicate the number of disc stars and outliers for each group, with 〈[Fe/H]〉 and stellar ages, t_★, presented. The number of stars likely to belong to the disc as well as the number of outliers are shown in the top legend box.