5 × 15 bins of the age-matallicity map that is sampled in this study. Patch colours match the colours of the points in Figs. B.2, B.4, and B.5. The vertical arrows indicate the sequence of five colours used in the top panels of these figures, and the horizontal arrows indicate this sequence in their bottom panels. The horizontal colour scheme follows the halo MDF (the green line in Fig. 3), that is, the darkest colour is used for the bin where the MDF peaks (Z = 0.001). The age bins for constant metallicity are also set such that the age bins with increasingly realistic ages for halo stars have darker colours (i.e. darker colours for older stars). To avoid confusion, the age values in the vertical sequence are set to be slightly different from those in the horizontal sequence.