Abstract
Radio sources can have such high luminosities that they are detectable at great distances. They may therefore be important tracers of the structure and evolution of the early Universe. They apparently evolve in time; compared with the present epoch, strong radio sources are orders of magnitude more common at redshifts z greater than unity1,2. Direct measurements of the number of radio sources observed as a function of their flux places constraints on both their evolutionary behaviour and on the cosmological models. To extend the present source counts to lower flux limits, the Very Large Array (VLA) of the National Radio Astronomy Observatory was employed. Thirteen widely separated fields at high galactic latitude were mapped at the VLA at 6 cm. The fields are 12.8 arc min square, and the 5σ noise levels extend below 1 mJy. The resulting differential source counts were ΔN/ΔN0 (0.5 mJy <S < 3.0 mJy) = 0.0384 and ΔN/ΔN0 (3.0 mJy < S < 10.0 mJy) = 0.178. These results confirm the deviation at low flux levels from the uniform N = 60 S−1.5 Ω distribution.
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