Studies of a sample of 6C radio galaxies at a redshift of 1 -: I.: Deep multifrequency radio observations

Deep radio observations at 5 and 8GHz are presented of a complete sample of 11 radio galaxies with redshifts 0.85 < z < 1.5, selected from the 6C sample of Eales. The radio data, taken using the Very Large Array in A, B and C array configurations, provide a best angular resolution of 0.25 arcsec and reach an rms noise level of the order of 20 mu Jy. Radio spectral index, radio polarization, and rotation measure maps are also presented for each source, and the radio data are compared with K-band infrared images of the fields of these sources, Radio core candidates are detected in eight of the 11 sources. Nine of the 11 sources display deviations from 'standard double radio source' morphologies, with multiple hotspots in one or both lobes, or a hotspot withdrawn from the leading edge of the radio emission. At 8 GHz, the sources are typically polarized at the 5 to 15 per cent level. The mean rotation measures of the individual lobes are, in all but one case, less than 50 rad m(-2), but strong asymmetries between the two lobes and steep gradients within some lobes indicate that the Faraday rotation does not have a Milky Way origin; rather, the distant 6C radio sources lie in a relatively dense clumpy environment. The sources are compared with the more radio powerful 3CR radio galaxies in the same redshift range, and with lour-redshift radio galaxies. The ratio of core to extended radio flux is found to be almost independent of the linear size of a radio source and only weakly inversely correlated with the total radio source power. This latter result indicates that the high radio luminosity of the most powerful radio sources must originate in a powerful active nucleus, in contrast to the suggestion of some authors that such sources are so luminous only because confinement by a dense surrounding environment boosts the lobe fluxes. Environmental effects must play a secondary role.