Average radial profiles of CO surface brightness and H₂ surface density. The x-axis is plotted in log scale. The solid lines represent the median values per radial bin, averaged across the galaxy sample shown in each panel. The shaded regions encompass the 16th and 84th percentiles of the values per radial bin. Each column shows a different redshift slice, as labelled at the top, whereas each row is for a different stellar mass bin, as indicated in the left of each row. Given the volume of SIMBA25, the highest mass bin contains the fewest galaxies. Only three CO transitions are shown, for clarity (legend at right).