Radio luminosity as a function of star formation rate for the sources in the FCOZGM sample. Objects are colour-coded according to whether they are classed as star forming in the MPA-JHU catalogue (classifications “STARBURST” or “STARFORMING”); some objects not classified as SFG in this way are clearly nevertheless on the radio to star formation rate relation for star-forming objects. All objects not so classified (including unclassified objects) are placed in the “non-SFG” sample. The line shows a plausible by-eye selection of a division between the two classes.