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Published online by Cambridge University Press: 14 August 2015
Observational evidence on the angular diameter-redshift relation using radio sources has, until recently, been confined to studies of the overall angular size. In this paper a different approach is described in which the very compact hot spots in radio sources are used as standard measuring rods. Such hot spots appear to be especially suitable for cosmological studies for the following reasons.
(a) Hot spots which contain one half or more of the total flux density are generally found only in the most powerful sources (P178 ≳ 1027 W Hz−1 sr−1).
(b) Hot spots appear to show a smaller dispersion in physical size than the overall source dimensions.