Correlated radio and optical asymmetries in powerful radio sources

We examine the spatial distributions of thermal emission-line gas and nonthermal radio-emitting plasma in powerful radio galaxies. At high redshifts and luminosities, the thermal gas is distributed very asymmetrically with respect to the galaxy nucleus. The one-sidedness of the emission line regions is clear evidence of an intrinsically asymmetric property of powerful radio sources. The radio sources are more asymmetric in their lobe spacings at high redshifts, but not at a highly significant level. The primary result of this investigation is that the extended optical line emission is brightest on the side of the closer of the two radio lobes in essentially all cases. This correlation appears to be largely independent of linear size, lobe flux density, redshift, and radio power. A preliminary investigation of lobe-dominated quasars reveals similar correlated radio and optical asymmetries. This demonstrates that the lobe distance asymmetries and the presence of thermal line-emitting gas are directly linked and provides the first direct evidence that environmental effects are responsible for the structural asymmetries of powerful radio sources. The implications for the classical light travel time determination of lobe advance speeds and the derived source ages are briefly discussed.