The surface density of gas, Σ_gas, versus the surface density of the star-formation rate, Σ_SFR (the “Schmidt–Kennicutt relation”; Kennicutt 1998b). We show the locations of three high-redshift radio galaxies: PKS 0529-549 (blue diamond; this work); 4C 41.17 (green circle), and MRC 0152-209 (magenta pentagon). The black squares denote the Galactic massive HCN clumps from Heiderman et al. (2010). The lines indicate the best-fit to the data presented in the respective works, including local star-forming galaxies and circum-nuclear starbursts (black; Kennicutt 1998b), gas-rich galaxies at z  ∼  1−3 (magenta; Genzel et al. 2010), and colour-selected star-forming galaxies at z  ∼  1.5 (green; Daddi et al. 2010). Solid and dashed lines refer to the best-fit for disk star-forming galaxies and mergers, respectively.