The relativistic formula for the observed angular sizes of cosmological objects is shown to be expressible as a power law function of (1 + redshift), providing a better framework for the interpretation of angular diameter-redshift diagrams for extragalactic radio sources. In the case of an assumed homogeneous Friedman world model, it is shown that the variation of angular diameter as the inverse of redshift in extended radio sources is consistent with the angular diameter-redshift relation for rigid rods, as modified by source linear size evolution, and perhaps luminosity-linear size correlation, but not by the latter alone. These results are shown to be consistent with a linear size evolution law of the form: l varies as the inverse of (1 + redshift) to the inverse of (1 + redshift-squared), over the density parameter range zero-0.2.
The Astrophysical Journal 08/1982; 260(1):37-43. DOI:10.1086/160230