Left: Kennicutt-Schmidt diagram for the target SMGs. The individual data points are colour-coded with the distance from the Speagle et al. (2014) MS as shown in the colour-bar on the right. The green and red filled circles represent the mean values of the binned MS and starburst data, where the latter population is defined as lying above the MS by a factor of > 3. Each bin contains four SMGs, and the error bars represent the standard errors of the mean values (see Table A.2). The green and red dashed lines represent the least squares fits to the binned data sets, the blue dashed line shows the K98 relationship, and the magenta and cyan dashed lines show the D10b relations for disks and starbursts, respectively. For reference, the yellow solid line corresponds to a constant global SFE of 10% per 100 Myr, which corresponds to a gas depletion time of τ_dep = 1 Gyr. Right: binned averages from the left panel compared with selected literature studies. The black triangles and yellow squares show the spiral galaxy and starburst data from K98, respectively, the red plus signs show the z = 1.10−2.43 star-forming galaxy data from Tacconi et al. (2010), the blue circles show the z = 1.414−1.6 BzK-selected disk galaxies from Daddi et al. (2010a), and the magenta diamonds represent the z = 1.21−2.49 SMG data from Bothwell et al. (2010). The arrows pointing left indicate upper limits to Σ_gas. The dashed lines have the same meaning as in the left panel.