Radial distributions of [Fe/H] of stars formed at different epochs. Each panel corresponds to one epoch, as indicated in the lower right corner. The filled contours show the distributions of young stars (<100 Myr) formed at this epoch, with levels corresponding to 0.01 and 1% of the stellar population. These stars are then tracked to the following epochs, and their evolved distributions are shown in the subsequent panels with line contours, but always keeping the same color across all panels.