Effect of choosing different lower observational limit for L _CII. Top left: time evolution of the observational surface for the four different L _CII lower limits considered. Top right: the Σ_SFR − Σ_CII relation. Bottom left: the [C II]/FIR ratio vs. Σ_FIR. Bottom right: the [C II]/FIR ratio vs. Σ_SFR. In all panels, the blue color is for L _CII > 0 L _⊙, orange for L _CII > 0.1 L _⊙, green for L _CII > 0.5 L _⊙ (the one we consider in the main text), and red for L _CII > 1 L _⊙. As can be seen, the observational limit does not affect the trends and the overall results presented.