On the interpretation of the observed angular-size-flux-density relation for extragalactic radio sources |
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Authors: | V K Kapahi V K Kulkarni C R Subrahmanya |
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Institution: | (1) Tata Institute of Fundamental Research, Post Box No. 1234, 560012 Bangalore;(2) Radio Astronomy Centre, Tata Institute of Fundamental Research, Post Box No. 8, 643001 Ootacamund;(3) Tata Institute of Fundamental Research, Post Box No. 1234, 560012 Bangalore |
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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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Keywords: | radio sources extragala ctic angular-size-flux-density relation cosmology radio sources evolution |
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