a: correlation between the [SIV]10.5 μm and [SIII]18.7 μm summed emission line luminosity, expressed in units of 10⁴¹ erg s⁻¹, and the SFR derived from the total IR luminosity (black dashed line) for a composite catalogue of SFGs (red star) and from the Hα luminosity (corrected for the IR luminosity) for LMGs (green triangles). The shaded green areas in the three plots indicate the 95% confidence interval. b: correlation between the [NeII]12.8 μm and [SIV]10.5 μm summed luminosities and the SFR derived from the total IR luminosity (black dashed line) for SFGs (red star) and from the Hα luminosity (corrected for the IR luminosity) for LMGs (green triangles). c: correlation between the [NeIII]15.6 μm and [SIII]18.7 μm summed emission lines and the SFR derived from the total IR luminosity (black dashed line) for SFG (red star) and from the Hα luminosity (corrected for the IR luminosity) for LMG (green triangles). In all three figures, the purple squares highlight the ULIRG population in the SFG sample.