Correlated radio and optical asymmetries in powerful radio sources

Abstract

The spatial distribution of the thermal line-emitting gas associated with powerful radio galaxies is examined, and the structural asymmetries of classic double sources are studied. The relation between the distributions of the thermal and nonthermal plasmas is used to investigate the cause of the observed radio source asymmetries. It is shown that the lobe distance ratios are strongly correlated with the presence of thermal line-emitting gas and that the closer lobe always lies on the same side of the nucleus as the high surface brightness optical line emission. This is the first direct evidence for an environmental origin of the lobe distance asymmetries in a complete sample of sources. This radio/optical relationship is extremely robust and appears to be largely independent of the source parameters. This result also holds for very small Q-asymmetries, suggesting that kinematic effects play a small role in producing apparent source asymmetries.