MAMBO 1.25 mm observations of 3CR quasars at z ~ 1.5: on the debate of the unified schemes

¹ Astronomisches Institut, Ruhr-Universität Bochum (AIRUB), Universitätsstr. 150 / NA7, 44780 Bochum, Germany e-mail: haas@astro.rub.de
² Radioastronomisches Institut, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
³ Instituto de Astronomía, Universidad Católica del Norte, Avenida Angamos 0610, Antofagasta, Chile

Received: 16 December 2004
Accepted: 2 September 2005

Abstract

In order to explore the nature of the 850 μm flux difference between powerful radio galaxies and steep radio-spectrum quasars at  reported by Willott et al. (2002), we have observed 9 sources from their sample of 11 quasars at 1.25 mm. For 7 sources the 1.25 mm 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 1.25 mm radiation. If we extrapolate a power-law synchrotron spectrum to shorter wavelengths, then for 6 of the 9 sources also the 850 μm 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.