2006A&A...445..115H

In order to explore the nature of the 850µm flux difference between powerful radio galaxies and steep radio-spectrum quasars at z∼1.5 reported by Willott et al. (2002MNRAS.331..435W), we have observed 9 sources from their sample of 11 quasars at 1.25mm. For 7 sources the 1.25mm fluxes are much brighter than one would expect from a purely thermal dust model fitted to the submm data, providing evidence for the synchrotron nature of the observed 1.25mm radiation. If we extrapolate a power-law synchrotron spectrum to shorter wavelengths, then for 6 of the 9 sources also the 850µm fluxes are dominated by synchrotron radiation. We discuss how far the (sub)-millimetre data can be interpreted in accordance with the orientation-dependent unified schemes for powerful radio galaxies and quasars. In this case the results challenge the reported evidence for the receding torus model and for the evolutionary trend of a declining dust luminosity with increasing projected size of the radio lobes.