On the injection spectrum of relativistic electrons in high-redshift radio galaxies

Abstract

We point out that the remarkable linearity of the ultra-steep radio spectra of high redshift radio galaxies reflects a previously reported general trend for powerful radio galaxies, according to which the spectral curvature is lesser for sources having steeper spectra (measured near rest-frame 1 GHz). We argue based on existing theoretical and observational evidence that it is premature to conclude that the particle acceleration mechanism in sources having straight, ultra-steep radio spectra gives rise to an ultra-steep injection spectrum of the radiating electrons. In empirical support to this we show that the estimated injection spectral indices, available for a representative sample of 35 compact steep spectrum (CSS) radio sources are not correlated with their rest-frame (intrinsic) rotation measures, which are known to be typically large, indicating a dense environment, as is also the case for high-$z$ radio galaxies.

5 pages, 1 figure; submitted on September 2, 2011; accepted for publication in Astrophysical Journal on October 17, 2011

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• Search and analysis of giant radio galaxies with associated nuclei (SAGAN) -- I : New sample and multi-wavelength studies
• Strong magnetic fields and large rotation measures in protogalaxies by supernova seeding
• High-resolution international LOFAR observations of 4C~43.15 -- Spectral ages and injection indices in a high-z radio galaxy
• A VLA-GMRT Look at 11 Powerful FR II Quasars
• A supernova scenario for magnetic fields and rotation measures in galaxies