Submillimetre photometry of typical high-redshift radio quasars

Abstract

We present submillimetre (SCUBA) photometry of a sample of eight high-redshift (2.5 < z < 3.5) radio quasars from two redshift surveys: the TEXOX-1000, or TOOT, survey; and the 7C Redshift Survey (7CRS). Unlike the powerful high-redshift radio sources observed previously in the submillimetre, these radio sources are typical of those dominating the radio luminosity density of the population. We detect just two of the TOOT/7CRS targets at 850 microns, and one of these detections is probably due to synchrotron emission rather than dust. The population represented by the other six objects is detected in a statistical sense with their average 850-micron flux density implying that they are similar to low-redshift, far-infrared-luminous quasars undergoing at most moderate (< 200 solar masses per year) starbursts. By considering all the SCUBA data available for radio sources, we conclude that positive correlations between rest-frame far-infrared luminosity, 151-MHz luminosity and redshift, although likely to be present, are hard to interpret because of subtle selection and classification biases, small number statistics and uncertainties concerning synchrotron contamination and K-correction. We argue that there is not yet any compelling evidence for significant differences in the submillimetre properties of radio-loud and radio-quiet quasars at high redshift.

arXiv comment11 pages, accepted for publication in MNRAS

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