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On the interpretation of the observed angular-size-flux-density relation for extragalactic radio sources

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Abstract

The interpretation of the observed relation between median angular sizes (θ m) of extragalactic radio sources and flux density at 408 MHz has been examined. The predictedθ m-S relations based on well-observed strong sources in parent samples selected at 178 and 1400 MHz, and existing models of the evolving radio luminosity function can be made to fit the observed relation only by invoking cosmological evolution in linear sizes even for theq 0 = 0 universe. Predictions based on a parent sample at 2.7 GHz are shown to overestimate the contribution of steep-spectrum, compact (SSC) sources in low-frequency samples unless the downward curvature in the spectra of such sources is taken into account. When approximate corrections are made for this effect, predictions based on the 2.7 GHz parent sample cannot obviate the need for linear size evolution as claimed in the literature.

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Authors and Affiliations

  1. Tata Institute of Fundamental Research, Post Box No. 1234, 560012, Bangalore

    V. K. Kapahi

  2. Radio Astronomy Centre, Tata Institute of Fundamental Research, Post Box No. 8, 643001, Ootacamund

    V. K. Kulkarni

  3. Tata Institute of Fundamental Research, Post Box No. 1234, 560012, Bangalore

    C. R. Subrahmanya

Authors
  1. V. K. Kapahi
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  2. V. K. Kulkarni
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  3. C. R. Subrahmanya
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Kapahi, V.K., Kulkarni, V.K. & Subrahmanya, C.R. On the interpretation of the observed angular-size-flux-density relation for extragalactic radio sources. J Astrophys Astron 8, 33–50 (1987). https://doi.org/10.1007/BF02714250

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  • DOI: https://doi.org/10.1007/BF02714250

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