DETECTION OF DUST IN THE MOST DISTANT KNOWN RADIO GALAXY

A search for millimetric continuum emission from eight optically selec ted, radio-quiet quasars and a radio galaxy with 3.7 < z < 4.3 has bee n undertaken using a highly sensitive seven-channel bolometer on the I RAM 30-m Millimetre Radio Telescope. Detections of a potentially dust- rich quasar, and of 8C 1435 + 635, the most distant known radio galaxy , are reported. An extrapolation of the steepening centimetric radio s pectrum of 8C 1435 + 635 accounts for less than 1 per cent of the obse rved 1.25-mm flux density, indicating that the emission is most likely from dust, although the present data cannot discriminate against sync hrotron emission. If the emission is thermal, then the derived dust ma ss lies in the range 2 x 10(9) > M(d) > 8 x 10(7) M. for 20 < T-d < 10 0 K, or M(d) similar to 1.6 x 10(8) M. for T-d = 60 K, similar to that derived for 4C 41.17, suggesting a molecular gas mass of between 4 x 10(10) and 9 x 10(11) M.. The quasar, PC 2047 + 0123 at z = 3.80, has no detectable centimetric emission and the 1.25-mm continuum detected here probably also originates from 1.5 x 10(8) M. of dust (again for T -d = 60 K). Upper limits have been obtained for four quasars, correspo nding to dust mass limits of about 3 sigma < 2 x 10(8) M.; less useful limits have been set for a further three quasars.