Variations of the linear sizes of extragalactic radio sources with radio luminosity and redshift

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Abstract
The variations with radio luminosity and redshift of the characteristic linear size of extragalactic radio sources are investigated in two ways: (1) by examining bright flux-density-limited samples in order to determine the dependence explicitly, and (2) by comparing angular size–flux density data from faint samples (which generally have no redshift information) with numerical predictions, using individual sources in bright samples to define the local population. These predictions, using multi-frequency space-density evolution models, divide the total population into flat- and steep-spectrum components, thereby allowing populations found at different frequencies to be related. These investigations suggest that the apparent local distribution of linear sizes is determined by instrumental and physical selection effects which result in a weak inverse correlation of linear size with radio luminosity. For populations at earlier cosmological epochs, these effects cause an apparent decrease in linear size with redshift, although not by enough to account for the observational results. These may thus point to a variation in the relative proportions of physically distinct types of source with redshift.

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