Distribution of the SFE per free fall time of the gas in the disc (r<40 ckpc) of simulation Au6_MOL, at 2, 6, 10, and 13.8 Gyr. The first row shows the distribution separated by metallicity ranges (the colour lines show the ranges while the black lines show the full distribution), and the second row shows the distribution separated by density ranges (ρ_th in the legend is the density threshold for SF). The blue arrows indicate the median of the total distribution (black line), while the red arrows indicate the median of the distribution for gas that has been transformed into stars (this distribution is not shown).