Dust heating fractions in a slice through the mid-plane of the face-on view of our model (left panels). The direction of the AGN beam is aligned with the horizontal axis of the figure. The colour code is set on the histograms on the right. The histograms contain all dust cells (including the ones above and below the midplane). Top row corresponds to f_young, middle row to f_old, and bottom row to f_AGN. The white contour corresponds to the 0.5% level in f_AGN and highlights an asymmetry in the heating of dust in the disc.