Predicted [C ii] (upper panel) and [O iii] (lower panel) luminosities (L) as a function of the incident flux (G) exciting the line, inferred by using the model presented in V16, in which the colour shading is done according to M_gas, as encoded in the colourbar. In each panel we plot with a horizontal green line the luminosity inferred from our observations of the [C ii] clump and of the [O iii] clump-I. The horizontal dashed green lines show the upper limits at the location of the Y-band image of BDF-3299. Additionally, we show the flux G expected from BDF-3299 at the location of the [C ii] and [O iii] clumps and also the estimated average G within the galaxy BDF-3299. See the text for details.