COMPACT SYMMETRICAL OBJECTS AND THE EVOLUTION OF POWERFUL EXTRAGALACTIC RADIO-SOURCES

Multifrequency radio observations of the compact symmetric objects 010 8+388, 0710+439 and 2352+495, and high-resolution VLA observations of the primary hot spot in Cygnus A, are used to investigate the dependen ce on external density of the size, pressure, advance speed, and flux density of the hot spots in powerful extragalactic radio sources. The relationships derived are applied over the whole range of scales obser ved in these objects. These relationships lead directly to a unifying evolutionary model for powerful radio sources, in which compact symmet ric objects evolve first into compact steep spectrum doubles, and then into large Fanaroff-Riley type II objects. We propose that this is th e primary evolutionary track for powerful extragalactic radio sources. The observations strongly suggest that these objects evolve substanti ally in luminosity, with little variation in expansion speed between 1 0 pc and 200 kpc.