Ratio of [Cii] and FIR luminosity as a function of FIR luminosity (left), FIR color (middle) and FIR surface brightness (right panel). Red lines indicate the fits to our sample (Eqs. (12) and (13)), and black lines results of Díaz-Santos et al. (2013). The two slightly outlying points marked with an overlayed asterisk in the right panel were not used for the fit that is shown in red. Suitable [Cii] data are available for the 182 galaxies that are plotted here.