It is shown that the fraction f(css) of compact steep spectrum (CSS) galaxies in a combined sample by Peacock and Wall (1981) and Wall and Peacock (1985) increases with a redshift greater than 0.2 according to the relation f(css) varies as (1 + Z) exp 2.1, with a cutoff for Z of less than 0.2. The fraction of CSS quasars remains fairly constant with redshift. It is concluded that for galaxies, the variation of f(css) with Z could give rise to the effect of linear size evolution in the angular diameter-redshift relation for an inhomogeneous sample, whereas for quasars nonrandom orientation can give rise to the same effect. The variation of f(css) with Z is explained in terms of the expansion into the interstellar medium of sources in an early stage of their development.
The Astrophysical Journal 01/1992; 386(2):452-454. DOI:10.1086/171030