We report observations of a sample of high redshift sources (1.8<z<4.7), mainly radio-quiet quasars, at 350 microns using the SHARC bolometer camera at the Caltech Submillimeter Observatory. Nine sources were detected (>4-sigma) and upper limits were obtained for 11 with 350 micron flux density limits (3-sigma) in the range 30-125mJy. Combining published results at other far-infrared and millimeter wavelengths with the present data, we are able to estimate the temperature of the dust, finding relatively low values, averaging 50K. From the spectral energy distribution, we derive dust masses of a few 10^8 M_sun and luminosities of 4-33x10^{12} L_sun (uncorrected for any magnification) implying substantial star formation activity. Thus both the temperature and dust masses are not very different from those of local ultraluminous infrared galaxies. For this redshift range, the 350 micron observations trace the 60-100 micron rest frame emission and are thus directly comparable with IRAS studies of low redshift galaxies.
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