Redshift dependence of the low-frequency turnover of quasars

Abstract

I have identified a sample of quasars whose spectra exhibit clearly defined maxima at low frequencies. The turnover frequencies are found to increase with redshift, but the equipartition angular sizes, deduced on the assumption of a synchrotron self-absorption model, decrease much faster than is predicted by any simple cosmological model. I show that this variation may be due to the steep density gradient of the gas in the nuclear regions of the parent galaxies and to the increase in number density or luminosity of the sources at earlier epochs.