A 22-GHZ VLBI SURVEY OF 140 COMPACT EXTRAGALACTIC RADIO-SOURCES

A sample of 140 compact, flat- or inverted-spectrum (alpha>-0.5, S(nu) similar to nu(alpha)) extragalactic radio sources with delta greater t han or equal to-40 degrees and total flux density S(nu)greater than or similar to 1 Jy has been observed with VLBI at 22 GHz on baselines of 4,400-10,800 km (3.3-8.0X10(8) lambda) spanning the Pacific Ocean. St ructural information on scales as small as similar to 150 mu as, in th e form of brightness temperatures or lower limits, has been derived fo r the 136 sources that were detected. Twenty-one sources show evidence of structure with brightness temperature in the source frame greater than 10(12) K. This survey was motivated by the needs of the Space VLB I missions VSOP and RadioAstron currently being prepared for launch. A mong the 84 sources detected on baselines longer than 7.0x10(8) lambda , 32 have fringe amplitudes greater than 1 Jy and 14 show evidence of structure with observed brightness temperature greater than 7.4X10(11) K, the 7 sigma detection threshold for a 1 Jy circular Gaussian sourc e on a 25,000 km baseline between VSOP and a single VLBA antenna at 22 GHz. The data obtained in this ''Pre-Launch Survey'' should prove use ful not only for these and future space VLBI missions, but also for st atistical studies of active galactic nuclei (AGN) and for planning mil limeter-VLBI experiments. Of particular interest is the prominence in the survey results of the 21 AGN that have been detected in gamma-rays by CGRO/EGRET [Thompson et al. ApJS, 101, 259 (1995)]. (C) 1996 Ameri can Astronomical Society.