An Angular Diameter-Redshift Test of Cosmological Models Using Observations of Weak Radio Sources

Recent observations with the Cambridge One-mile radio telescope provide angular diameter data for sources having a wide range of flux densities. These enable cosmological models to be tested by comparing the number of sources of large angular diameter at different flux densities. On the basis of different world models, and the known distribution of the physical sizes of 3C sources, the expected numbers of extended sources in the 5C surveys are calculated. Significantly more sources of large diameter are found to be present in the 5C samples than are predicted by simple models; this excess may be explained by incorporating cosmological evolution. It is concluded that evolutionary changes are associated with the population of large diameter radio sources, which generally have radio luminosities in the range $${10}^{24}\lt{P}_{178}\lt{10}^{26}\,\text{W}\,\text{Hz}^{-1}\,\text{sr}^{-1}$$, but that the changes are much less than those required for more powerful sources $$({P}_{178}\gt{10}^{26}\,\text{W}\,\text{Hz}^{-1}\,\text{sr}^{-1})$$ in order to satisfy the total source counts.