CO(1–0) line luminosity as a function of the nebular visual extinction for the sample of local star-forming galaxies defined by the ALLSMOG survey and by the sub-sample of COLD GASS selected in Sect. 5. The left and right panels shows the A_V values obtained by using the attenuation curves proposed by Cardelli et al. (1989) and Calzetti et al. (2000), respectively. Further explanation relevant to the quantity plotted on the y-axis, the symbols and the regression analysis can be found in the caption of Fig. 8 and in the text (Sect. 7). Since the typical uncertainty on A_V is very large, of the order of ~ 0.5 mag, the fit was performed without accounting for the measurement error on x, in order to not bias the results (see discussion in Kelly 2007). For the same reason the plots do not show error-bars in the x direction.