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Paper: Radio SEDs of High-redshift Radio Galaxies
Volume: 380, At the Edge of the Universe: Latest Results from the Deepest Astronomical Surveys
Page: 213
Authors: Klamer, I.J.; Ekers, R.D.; Hunstead, R.W.
Abstract: The correlation between the redshift of a radio galaxy and the steepness of its observed radio spectral index has proven to be the most efficient way to find the most massive galaxies at high redshift. Since the vast majority of high-redshift radio galaxies are found by exploiting this correlation, it is critical that its origin is understood. The conventional interpretation for the redshift-radio spectral correlation is based on the k-correction of a curved spectral energy distribution that steepens toward higher frequencies. However, we have found that high-redshift, steep spectrum radio galaxies are very well characterised by power laws, and therefore the k-correction interpretation of the z−α correlation is incorrect. Here, we suggest instead that evolution in the density of the IGM could be driving this correlation. Since massive, steep-spectrum radio galaxies in the local universe usually reside at the centres of rich galaxy clusters, we argue that a natural interpretation for the correlation is that radio galaxies at high redshift are located in environments with densities similar to nearby rich clusters.
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