2003MNRAS.344L..74P

We present submillimetre (submm) continuum observations of a sample of some of the highest redshift quasars currently known, made with the Submillimetre Common-User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope (JCMT). 12 of the sample have redshifts z > 5 and two have z ≥ 6; the median redshift of the sample is 5.3. Two of the z > 5 objects are strong (6σ) detections, and are bright sources with S_850µm> 10 mJy. Another firm (5σ) detection is obtained for the z 5.7 quasar SDSS J1044-0125; SDSS J1306+0356, at z 6.0, is detected with a signal-to-noise ratio ~4. We have obtained sensitive (σ~ 1.5 mJy) upper limits for much of the remainder of the sample, including the z 6.3 quasar SDSS J1030+0524.

Submm spectral indices measured for two of the sources (α~ 3.3) are consistent with thermal reradiation from dust, rather than from synchrotron emission. Sensitive upper limits at 450 µm imply that the dust is cool, requiring large dust masses (10^8–9 M_☉) to account for the observed fluxes, suggesting substantial prior star formation - even at z 6, when the Universe was only 1.0 Gyr old.