A study of spectral ageing in the radio galaxy 3C 234 and its implications

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Abstract
Radio data from the VLA and 5-km telescope at five frequencies and at a resolution of 5.0×8.3 arcsec2 have been used to determine the variation of spectrum across 3C 234. The results are a good fit to the standard model in which relativistic electrons are accelerated in the hotspots and lose energy as they move out into the lobes. Electrons in the region surrounding the eastern hotspots are found to have suffered anomalously large energy losses – perhaps because of sudden adiabatic expansion. There is evidence for re-acceleration in the western lobe near to the central source, probably due to stochastic acceleration in fluid-dynamical turbulence. The dynamics of the radio-emitting plasma are investigated by means of the ageing analysis and inferred magnetic field directions. A model invoking bulk transport in the plasma due to backflow, and/or galactic motion with respect to the 3C 234 cluster, appears to be the most plausible. The age analysis, shape of the source and magnetic field configuration all suggest the existence of backflow in the eastern lobe which has been deflected by the presence of the host galaxy.

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