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Published December 1980 | Published
Journal Article Open

Models of the cosmological evolution of extragalactic radio sources – I. The 408-MHz source count


A simple numerical procedure for analysing the counts of extra-galactic radio sources is described. The scheme makes efficient use of the extensive data base which is now available for studying the spatial distribution of radio sources. The method is first applied to data at 408 MHz. We show that, if proper statistical testing is incorporated, the technique provides strong support for the qualitative conclusions of previous analyses: the comoving density of the more powerful radio sources with extended structure is now less than at earlier epochs by a factor of ≳ 10³. However, several evolution models proposed earlier are quantitatively unsatisfactory, and new models are derived which adequately describe the current data. These new models make contrasting predictions about redshift distributions amongst the faint radio sources (S₄₀₈ ≽ 10 mJy), and identification data at such levels can therefore provide powerful constraints upon the models. Our results are compared with results from recent investigations of the spatial distribution of steep-spectrum radio sources.

Additional Information

© 1980 Royal Astronomical Society. Provided by the NASA Astrophysics Data System. Received 1980 March 27; Published: 01 December 1980. We thank Peter Warner for help and advice on computing techniques. JVW gratefully acknowledges support of the Royal Society via a Jaffe Donation Research Fellowship held during the course of this work.

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