Intrinsic radio spectra and structural asymmetry of powerful radio galaxies

Abstract

For a well-defined sample of 95 Fanaroff-Riley type II (FR II) radio galaxies selected from the 3CR complete sample, radio spectral indices of individual sources have been evaluated in their rest frames, after subtracting the known contribution of the radio core from the integrated emission. We find that, on average, the powerful radio galaxies that have a very steep spectrum at rest-frame frequencies near 1GHz show relatively small spectral curvature, compared with those that have a normal spectrum. Also, a new correlation is found, according to which radio spectra are more curved for sources with larger core-to-hotspot separation ratios (asymmetry parameter). These results provide potentially useful clues about the evolutionary pattern for double radio sources, which are briefly discussed.