A search for millimetric continuum emission from eight optically-selected , radio-quiet quasars and a radiogalaxy with 3.7 < z < 4.3 , has been undertaken using a highly sensitive 7-channel bolometer on the IRAM 30-m Millimetre Radio Telescope .
Detections of a potentially dust-rich quasar , and of 8C1435+635 , the most distant known radiogalaxy , are reported .
An extrapolation of the steepening centimetric radio spectrum of 8C1435+635 accounts for less than one per cent of the observed 1.25-mm flux density , indicating that the emission is most likely from warm dust , although the present data can not discriminate against synchrotron emission .
If the emission is thermal , then the derived dust mass lies in the range , 2 \times 10 ^ { 9 } < M _ { d } < 8 \times 10 ^ { 7 } M _ { \odot } for 20 < T _ { d } < 100 K , or M _ { d } \sim 1.6 \times 10 ^ { 8 } M _ { \odot } for T _ { d } = 60 K , similar to that derived for 4C41.17 , suggesting a molecular gas mass of between 4 \times 10 ^ { 10 } and 9 \times 10 ^ { 11 } M _ { \odot } .
The quasar , PC2047+0123 at z = 3.80 , has no detectable centimetric emission and the 1.25-mm continuum detected here probably also originates from 1.5 \times 10 ^ { 8 } M _ { \odot } of dust ( again for T _ { d } = 60 K ) .
Upper limits have been obtained for four quasars , corresponding to dust mass limits of around 3 \sigma < 2 \times 10 ^ { 8 } M _ { \odot } ; less useful limits have been set for a further three quasars .