Radio galaxies, quasars, and cosmology

This paper discusses the role of radio observations of galaxies and quasars in observational cosmology. Particular emphasis is given to the interpretation of radio-source counts, and it is concluded that when properly analyzed, the counts are not a function of wavelength, and that the claims for a large observed excess of weak sources have been greatly exaggerated. Evidence for a nonuniform spatial distribution of radio sources is inconclusive, and rests on (a) the significance of a small deficiency of relatively strong sources, (1)) the nature of the unidentified sources, and (c) whether or not quasar red shifts are in fact of cosmological origin. The rather pronounced change in number density observed between 5 and 10 sources , the apparent angular distribution, and the absence of any observed spectral index-flux density relation suggest that the data may not be cosmologically relevant. In particular, the radio-source counts do not provide evidence for cosmic evolution independent of the distribution of quasar red shifts. The dependence of observed angular size of radio sources on flux density and red shift is also examined, and it appears to reflect an apparent change in linear dimensions with red shift, rather than the effect of space curvature, and appears to be of little value in distinguishing between various world models. Finally, the apparent "super-light" motions of quasar components is discussed and it is concluded that the simplest explanation of the data suggests that the sources are nearer than indicated by their red shift, and that either the motions are non relativistic or there are no real motions at all and only variations in the intensity of one or more stationary components.