Comparisons between the ¹²CO (J = 2−1) velocity-integrated luminosity (L_CO, left), IRAS 60 µm luminosity (L_{60 µm}, middle), and bolometric luminosity (L_bol) with the luminosity in the GALEX NUV and FUV bands (top and bottom panels, respectively). The colour-coding used for variability types is shown in the top left panel. Triangles are upper limits. The dashed line represents the best linear fit to the F₆₀-to-L_NUV data points (Pearson’s correlation coefficient r = −0.48). The trends in the rest of the variables represented have not been confirmed (Sect. 7.2).