A General Discussion of the Distribution of Brightness of Extragalactic Radio Sources

The paper contains a description and discussion of the brightness distribution of extragalactic radio sources based mainly on recent observations at the California Institute of Technology. The paper con- centrates on displaying general properties of radio sources rather than a discussion of individual sources. In § II the angular scale and the morphological types of radio structures are discussed. Approximately one-third of the sources are true doubles composed of two similar components. Other common structure types are complex sources, core-halo sources, and double sources whose components have unequal diameters. However, many of these sources still show a double-type symmetry. Sources with simple structures are rare. In § III a method is outlined for analyzing the structure of a large sample of sources by using the visibility function. The section gives the distributions of angular size, percentage and size of fine struc- ture, "symmetry," and "compactness" of radio sources determined by use of this method. A comparison of the radio structure with optical structure, radio luminosity, and radio diameter suggests that the gross radio structure depends only on the radio luminosity. Furthermore, as a component recedes from a galaxy, its diameter expands at a velocity proportional to the recessional velocity. This type of component evolution defines a "cone of ejection" from the galaxy with an opening of ~-~25° for the more luminous sources and ~j5O0 for the weaker sources. In § IV the spatial properties of the radio structure and the galaxy are discussed. For double sources the galaxy lies close to the midpoint of the two components, perhaps a bit closer to the stronger com- ponent. For the doubles with unequal diameters, the galaxy is definitely situated closer to, sometimes coincident with, the smaller-diameter component. It is suggested that some of these sources are similar to 3C 83.1 (NGC 1265). The galaxy is coincident with the core component of core-halo sources. Variable radio galaxies tend to have a core-halo structure, and it is suggested that the halo and the core are the same age since halo-type components are not observed alone. Most complex sources are probably genet- ically related to the simpler sources