Surface density of star formation compared to gas (cold molecular + neutral) density gas (K–S diagrams; Kennicutt 1998). This figure has been adapted from Fig. 2 in Daddi et al. (2010a). The coloured areas roughly enclose different galaxy types indicated with labels. The black solid line (‘disks sequence’) is a fit to local spirals and z ∼ 1.5 BzK selected galaxies (slope of 1.42). The upper dashed line is the same relation shifted up by 0.9 dex to fit local U/LIRGs and SMGs. The dot-dashed purple line corresponds to a star formation suppression of a factor of 10 relative to the disks sequence. The coloured symbols are different locations of 4C12.50 for the diversity of parameters used in our calculations. The triangles correspond to cases A and the circles correspond to cases B in Table 5. The black diamond comes from Lanz et al. 2016 (case C). The triangles represent the values obtained from recent high angular resolution ALMA CO(2–1) data.