Relationship between the distance from the L(Hα)_{24 μm} vs. L(Hα)_BD relation and different parameters characterising the physical properties of the target galaxies, determined as described in the text. Filled dots are for galaxies with a normal gas content (HI - def ≤ 0.4), empty symbols for gas-poor objects (HI - def > 0.4). Black symbols are for galaxies with σ [C(Hβ)] ≤ 0.1, red symbols for σ [C(Hβ)] > 0.1. ρ gives the Spearman correlation coefficient for each panel for the whole sample (black and red; 152 objects) or for galaxies with high signal-to-noise in the spectroscopic data (σ [C(Hβ)] ≤ 0.1; black; 69 objects).