Upper panel: model CO spectral line energy distributions (SLEDs) of the local spiral, ULIRG, submillimeter, and high-z star-forming galaxies. The thick solid line corresponds to a constant brightness temperature. Lower panel shows the mean model CO SLEDs of our galaxy samples. For direct comparison with Fig. 8 of Daddi et al. (2015), the CO(1–0) emission of all galaxies was set to I_CO = 0.2 Jy km s^-1.