Top: similar to Fig. 1, but all the Σ_gas values were calculated by scaling the dust-based gas masses by a factor of 0.8 / 6.5 to make them consistent with a ULIRG α_CO conversion factor of 0.8 M_⊙ (K km s^-1 pc²)^-1. Bottom: similar to the top panel, but only the starburst SMGs’ Σ_gas values were calculated by using the aforementioned ULIRG α_CO factor, while a Galactic value was assumed for the MS objects. The plotting ranges of the two panels are different for legibility purposes.