Top: correlation of the fraction of [C II] emission from the ionized gas with the model parameters: the electron density (left panel) and the ionization parameter (right panel). Values of component #2 are plotted in case of mixed models. Spearman’s rank correlation coefficient and significance of its deviation from zero in parenthesis are indicated in the top-right corner. Bottom: distribution of ionization parameter values from the models with the observed galaxy metallicity. A horizontal line links the two U-values in the case of mixed models. In all panels, the data points are color coded by metallicity.