1.25-MM CONTINUUM OBSERVATIONS OF VERY-HIGH-REDSHIFT QSOS - IS THERE DUST AT Z=4.69

We report the results of 1.25-mm observations with the IRAM 30-m teles cope of five optically selected QSOs, and five radio-selected QSOs wit h high redshifts. Five of the QSOs have redshifts greater than 4. One of the radio-quiet, optically selected QSOs, BR1202 - 0725 (z = 4.69), was detected at > 3sigma. The observed flux of 10.5 +/- 1.5 mJY (lamb da(rest) = 220 mum) is similar to that of the high-luminosity IRAS sou rce F10214 + 4724 at z = 2.29 and, under the assumption that the detec ted emission is due to thermal emission from dust with a single temper ature (80 K), the inferred dust mass is approximately 4 x 10(8) M. (OM EGA0 = 1, H-0 = 50 km s-1 Mpc-1). If the FIR spectrum is similar to th at of F10214 + 4724, the FIR luminosity is approximately 10(14) L.. We discuss the detectability of thermal dust-like spectra and show that, for a dust spectrum with T(d) = 80 K, the detectability for constant mass increases almost linearly with redshift between redshifts of 1 an d 10. For the radio-loud QSOs the 1.25-mm observations indicate a stee pening of the radio continuum, from a median spectral index of + 0.3 b etween 20 and 6 cm to approximately -0.7 over the range 6 cm to 1.25 m m.