Schmidt–Kennicutt relations estimated from our model galaxies at both the galaxy scale and GMC scale. In the three panels the solid blue line indicates the Kennicutt (1998) relation. The grey shaded area is the distribution of a full sample of star-forming galaxies in the redshift range z = 1.5–2.1. Each coloured point indicates the position of an individual star-forming galaxy, uniformly selected within the galaxy-scale Σ_gas − Σ_SFR plan. The colour bar indicates the fragmented gas fraction in each representative galaxy. Left panel: the solid orange line is the best fit computed for our entire sample of star-forming galaxies within this redshift range. The dashed contour indicates measurements of nearby galaxies (Bigiel et al. 2008). The blue stars and points are from the starburst and normal disk galaxy samples from Kennicutt (1998), respectively. Central panel: the solid black line indicates the median trend of our star-forming galaxy sample. The dashed black lines indicate the 15% and 85% percentiles ranges of our model galaxies. We estimate an average scatter in the distribution of 0.46 dex. Right panel: distribution of galaxies in the Σ_gas − Σ_SFR estimated over the GMC-scale of star formation (see text for details). We show this estimate for the same galaxy sample used in the galaxy-scale Schmidt–Kennicutt relation in the two leftmost plots in this figure.