L_[C II/SFR ratio as a function of metallicity. Left panel: simulations compared with observed galaxies. Contours show where 90% (solid) and 50% (dashed) of the galaxies of the respective simulation lie. Right panel: the different ISM phases (DIG, atomic and molecular) in REF-L0100N1504. For the atomic phase, the L_[C II/SFR increases with decreasing metallicity. For the molecular phase, it also decreases with increasing metallicity but plateaus at ∼1 Z_⊙. For the DIG phase, it remains more or less constant.