A 22 GHz VLBI Survey of 140 Compact Extragalactic Radio Sources

Abstract

A sample of 140 compact, flat- or inverted-spectrum (α &gt; - 0.5, S<SUB>nu</SUB> ~ ν<SUP>alpha</SUP>^) extragalactic radio sources with δ &gt; - 40^deg^ and total flux density S<SUB>nu</SUB>_ &gt;~ 1 Jy has been observed with VLBI at 22 GHz on baselines of 4,400-10,800 km (3.3 - 8.0 x 10^8<SUP>lambda</SUP>) spanning the Pacific Ocean. Structural information on scales as small as ~150 µas, in the form of brightness temperatures or lower limits, has been derived for 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 VLBI missions VSOP and RadioAstron currently being prepared for launch. Among the 84 sources detected on baselines longer than 7.0 x 10^8^ λ, 32 have fringe amplitudes greater than 1 Jy and 14 show evidence of structure with observed brightness temperature greater than 7.4 x 10^11^ K, the 7σ detection threshold for a 1 Jy circular Gaussian source 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 useful not only for these and future space VLBI missions, but also for statistical studies of active galactic nuclei (AGN) and for planning millimeter-VLBI experiments. Of particular interest is the prominence in the survey results of the 21 AGN that have been detected in γ-rays by CGRO/EGRET [Thompson et al. ApJS, 101, 259 (1995)].