E − L_z space of in situ (first column), satellite (second column), and total (third column) star particles in the simulation, colour-coded at each point with the mean metallicity, when the analysis is restricted to a solar-like volume. The first row shows the E − L_z space in the case of an initial vertical metallicity gradient only. Likewise, the second row shows it, but in the case of an additional initial radial metallicity gradient. The scales of the colour bars are different depending on which galaxy is considered, in order to make their specific metallicity patterns emerge in a more evident way. We recall that in these plots stars on prograde orbits (which rotate as the disc) have negative L_z, while stars on retrograde orbits have positive L_z.