Submillimetre observations of z > 6 quasars

We report on submillimetre (submm) observations of three high-redshift quasars (z > 6) made using the SCUBA camera on the James Clerk Maxwell Telescope (JCMT). Only one of the sample was detected (>10sigma significance) at 850 mum - SDSS J1148+5251 (z= 6.43). It was also detected at 450 mum (>3sigma significance), one of the few quasars at z > 4 for which this has been the case. In combination with existing millimetric data, the 850- and 450-mum detections allow us to place limits on the temperature of the submm-emitting dust. The dust temperature is of no trivial importance given the high redshift of the source, since a cold temperature would signify a large mass of dust to be synthesized in the little time available (as an extreme upper limit in only 0.9 Gyr since z=infinity). We find, however, that the combined millimetre and submm data for the source cannot simply be characterized using the single-temperature greybody fit that has been used at lower redshifts. We discuss the results of the observing and modelling, and speculate as to the origin of the deviations.