The Milliarcsecond Structure of a Complete Sample of Radio Sources. II. First-Epoch Maps at 5 GHz

We have conducted a VLBI survey of a complete, flux-density-limited sample of 65 extragalactic radio sources, selected at 5 GHz. We have made 5 GHz images with a resolution ~0.001" of 37 of the sources using the Mark II system, and VLBI images are available for a further five sources. We have classified the sources into a number of groups with similar characteristics, based on the VLBI maps of the sources, their large-scale structure, and their radio spectra. We have examined the radio polarization, variability, largest angular size, alignment of large-scale and small-scale structure, and optical identification of the sources in each of the classes. One class, compact double sources with steep high-frequency spectra, is distinguished from the other classes by all these criteria: they show low polarization, little variability, and no large-scale structure, and are identified with galaxies. The majority of sources, however, can be grouped into classes that show a regular progression of properties consistent with the increasing prominence of the jet in a "core-jet" structure. One-sided jetlike structures are found in all classes except the very compact sources and the compact S doubles. No two-sided jets are found. In cases where both a VLBI (parsec-scale) jet and a kiloparsec jet are seen, the VLBI jet is on the same side as, or is connected with, the kiloparsec jet. Large misalignments are common. Superluminal motion is common and has been found in many of the classes, with the notable exception of the compact double sources.