SFHs of the first half of the IMPs. The top panel in each plot pair shows the SFH weighted by the stellar population’s luminosity at 4020 Å, whereas the bottom panel shows the mass-weighted SFH. Here, the black arrow marks the time where half of the galaxy’s mass was assembled, as indicated by the t_1/2 inset. The bar colours correspond to the stellar metallicity as indicated by the numbers above each plot pair, in units of Z_⊙.