We present 1.1-mm observations for a sample of 16 powerful radio galaxies at 0.5 < z < 5.2 and a radio-quiet quasar at z = 6.3, obtained using the AzTEC bolometer array mounted on the Atacama Submillimetre Telescope Experiment (ASTE) or the James Clerk Maxwell Telescope (JCMT). This paper more than doubles the number of high-z radio galaxies imaged at millimetre/submillimetre wavelengths. We detect probable millimetre-wave counterparts for 11 of the active galaxies. The six active galaxies that do not have a probable millimetre counterpart in our images nevertheless have one or more likely associated millimetric source. Thus, we conclude that powerful (radio-loud) active galaxies at high-z are beacons for finding luminous millimetre/submillimetre galaxies at high-z. The flux densities of our AzTEC counterparts imply star formation rates ranging from <200 to ∼1300 M⊙ yr−1. In addition, we find that for the radio galaxies the 1.1-mm flux density is anticorrelated with the largest angular size of the radio source.
We also present new Spitzer imaging observations of several active galaxies in our sample. Combining these with archival data, we examine the mid-infrared colours of our sample. We find that radio galaxies for which we have detected a probable 1.1-mm counterpart have mid-infrared colours consistent with dusty starbursts, and are usually bluer than high-z Spitzer-selected active galaxies. In addition, we find arcs of 24-m sources extending across ∼200–500 kpc, apparently associated with three of the radio galaxies.