INTRINSIC RADIO SPECTRA AND STRUCTURAL ASYMMETRY OF POWERFUL RADIO GALAXIES

For a well-defined sample of 95 Fanaroff-Riley type II (FR II) radio g alaxies 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 integrat ed emission. We find that, on average, the powerful radio galaxies tha t have a very steep spectrum at rest-frame frequencies near 1 GHz 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 potenti ally useful clues about the evolutionary pattern for double radio sour ces, which are briefly discussed.