Radio studies of complete samples of QSOs from the 4C and Parkes catalogs

The radio structures of more than 100 QSOs have been examined with 0.5'' resolution at 2695 and 8085 MHz. The results are combined with earlier data to provide structure information for the QSOs in observationally complete samples compiled from the 4C (178 MHz) and Parkes (2700 MHz) surveys by Wills and Lynds.About 70% of the Parkes sources, but fewer than 20% of the 4C sources, are smaller than 0.5''. This difference is related to the large population of flat-spectrum sources in the Parkes survey and is consistent with the incidence of flux density variability that is revealed when the new data are compared with observations made at Parkes. Comparison of the radio positions of the unresolved sources with optical positions of 0''.5 rms accuracy shows that the new radio positions have rms accuracy of about 0.4'' in R.A. and 0.75'' in decl.The largest angular sizes (LAS) of the sources are strongly correlated with radio spectra index and with redshift. The LAS--redshift correlation is in qualitative agreement with the hypothesis that QSO redshifts are cosmological in origin, and there is support for the presence of cosmological evolution of the linear sizes of QSOs. There is also a correlation between radio spectral index and redshift for the 4C QSOs with LAS>3'', which may represent a correlation between intrinsic radio luminosity and spectral index for the extended sources.The LAS distributions among QSOs in the complete 4C samples are compared with predictions based on data for 3CR QSOs, and it is found that the distributions are reproduced with cosmological number density evolution of the same amount as that indicated by Wills and Lynds's independent V/V/sub m/ tests of the same samples. The similarity of the 3CR and 4C LAS distributions sets limits to the amount of linear size evolution and, combined with the LAS--redshift results, suggests that there may be linear size evolution of the form (1+z)/sup -k/ with k<1--2