86 GHz VLBI survey of compact radio sources

We present results from 86 GHz VLBI1 observations of 28 compact radio sourc es made in April 1993. All but two of the observed objects are active galac tic nuclei. The remaining two objects are the galactic center Sgr A* and th e X-ray binary star Cygnus X-3. Of the observed sources, 26 have yielded fr inge detections. We present correlated flux densities, estimate the maximum observed brightness temperatures, and provide single Gaussian component mo del fits. Out of the 17 sources with good uv-coverages, 3 are without detec table structural details (0642+449, 0716+714, and Cygnus A), 3 have little closure phase information (4C67.05, 1823+568, and 1928+738), and the remain ing 11 have been imaged. We study the brightness temperatures, T-b, of the observed sources, and apply a basic population model with a single Value of the intrinsic brightness temperature, T-0, in order to reproduce the obser ved distribution of T-b Our data are consistent with a population of source s that have T-0 less than or equal to 5 x 10(10) K in the jets, and T-0 sim ilar to 1-4 x 10(11) K in the VLBI cores. The observed T-b are also correla ted with the apparent speeds measured in the jets. For comparison, we apply the same population scenario to a larger sample of 132 AGN observed with V LBI at 15 GHz, and show that the distribution of brightness temperatures fr om that sample is consistent with the intrinsic brightness temperature of T -0 = 5.3 x 10(11) K. The observed decrease of T-b along the jets can be rep roduced by adiabatic losses in relativistic shocks embedded in the jet.