SUBMILLIMETER OBSERVATIONS OF RADIO-QUIET QUASARS AND A LUMINOUS SEYFERT-1 GALAXY INCLUDING THE 1ST DETECTIONS

We report submillimeter continuum observations of six radio-quiet active galactic nuclei selected for high IRAS flux, in order to test models for the infrared continuum by constraining the far-infrared/submillimeter cutoff slope. Slopes greater than the self-absorbed synchrotron cutoff alpha(cutoff) = 2.5 (f(nu) is-proportional-to nu(alpha)) argue against the synchrotron model and lend support to the dust model. (The synchrotron cutoff slope can be slightly sharper than 2.5 if concave electron energy distributions and extreme homogeneity are assumed.) We detected the luminous Seyfert 1 galaxy PG 1434 + 590 at 438 and 345 mum; combining these detections with the IRAS 100 mum flux gives a slope of 2.53 +/- 0.17. Using our observed submillimeter upper limits for the radio-quiet quasars, we were able to constrain the cutoff slopes such that alpha(cutoff) > 2.50 in two cases (data for three others do not provide significant slope constraints). We conclude that the dust model is favored, but that synchrotron emission cannot yet be ruled out conclusively. In a related program we also observed and detected the z = 2.546 gravitationally lensed quasar H 1413 + 117, the " cloverleaf," at 345, 438, and 761 mum. The slope between 438 and 761 mum (observed; 124-215 mum rest frame) in this object is found to be 2.95 +/- 0.69. We suggest that in H 1413 + 117 we may be seeing a highly luminous but otherwise rather normal far-infrared peak shifted well into the submillimeter region.