Forty-one extragalactic objects including radio quiet quasars, radio loud quasars, and blazars (BL Lac objects and OVV quasars) have been observed at a wavelength of one millimeter. The measured 1mm flux densities agree with direct extensions of the radio continua of blazars and radio loud quasars. Furthermore, for the blazars, the 1mm flux density is correlated with an extrapolation of the power law infrared continuum. This result is supportive of a model in which the radio through optical continuum of blazars is beamed synchrotron radiation from a relativistic jet.
No radio quiet quasar was detected at a wavelength of 1mm to a limiting flux density of 1 Jy. The steep inverted radio continua characteristic of synchrotron self-absorption and free-free absorption models for radio quiet quasars are incompatible with the 1mm flux density upper limits. The "quiet" radio continuum from a relativistic jet oriented away from the observer's line of sight is consistent with the 1mm observations. A Comptonization model for quasar infrared emission, in which low frequency photons are upscattered by a thermal plasma will be in accord With the 1mm and infrared data provided the frequencies of the soft photons are in the range 1012 to 1013 Hz.
Repeated measurements have established that the 1mm flux densities of 3C273, BL Lac, 3C84, OJ 287, and 3C345 are variable on the time scale of a few months. Emission outbursts of blazars occur simultaneously and have similar amplitude at wavelengths of 1mm and 2cm. This result cannot be accounted for in the canonical expanding source model of radio variability; injection-type models, in which emission variability is governed by a change in the number of radiating electrons are preferred.
Three of the quasars undetected at a wavelength of 1mm have high redshift and anomalously low Lα/Hα emission line ratios. The 1mm flux density upper limits are used to constrain the temperature of a hypothetical dust shell with optical depth sufficient to account for the emission line ratio discrepancy.
The development of the composite germanium bolometer and lead light cone used for the 1mm quasar observations is described in the Appendix.
