Asymmetry of jets, lobe length and spectral index in quasars

ABSTRACT The less depolarized lobe of a radio source is generally the lobe containing the jet(Laing-Garrington correlation) but the less depolarized lobe is also generally thatwith the flatter radio spectrum (Liu-Pooley correlation). Both effects are strong; takentogether they would imply a correlation between jet side and lobe spectral index,i.e. between an orientation-dependent feature and one which is intrinsic. We test thisprediction using detailed spectral imaging of a sample of quasars with well-defined jetsand investigate whether the result can be reconciled with the standard interpretationof one-sided jets in terms of relativistic aberration. Our central finding is that thespectrum of high surface brightness regions is indeed flatter on the jet side, but thatthe spectrum of low surface brightness regions is flatter on the side with the longerlobe. We discuss possible causes for these correlations and favour explanations interms of relativistic bulk motion in the high surface brightness regions and differentialsynchrotron ageing in the extended lobe material.Key words: galaxies: jets – quasars: general – radio continuum: general