Hybrid morphology radio sources and the Fanaroff-Riley dichotomy

Abstract

We highlight a group of peculiar double radio sources we christen HYMORS: HYbrid MOrphology Radio Sources. These HYMORS appear to have an FR I type radio lobe on one side of the active nucleus but an FR II type lobe on the opposite side. Such objects range in size from ~0.01 Mpc to ~1 Mpc. The mere existence of these hybrid sources causes severe difficulties for models which attribute the differences between FR I and FR II radio sources to some intrinsic property of the compact central engine, or the composition of the jet plasma. HYMORS support models for the FR dichotomy based upon the interaction of the jet plasma with the ambient medium, in that asymmetries in the external environment could more naturally produce the observed hybrid morphologies.