CO line ratios as a function of galaxy properties: L_IR (top left), SFR (top middle), molecular gas depletion timescale due to star formation τ_dep ≡ M_mol/SFR (top right), molecular gas mass M_mol (computed by using the average α_CO derived in this work; bottom right), L_AGN (bottom middle), and AGN fraction (L_AGN/L_bol; bottom right). We show the binned values using darker colors, overplotted on the individual data points. Dashed lines indicate the best-fit relations obtained from a least squares regression analysis conducted for each transition line separately. The color coding refers to different line ratios, as indicated in the legend at the top-right corner of each plot.