Beamed Radiation in Radio Galaxies

Abstract

This paper focuses on two aspects of the Physics of Radio Galaxies in which it has been proposed that relativistic beaming of radiation is necessary to account for the observations. Physical arguments are presented which show that it is quite plausible that the jets in FRI radio galaxies are relativistic on the parsec scale and decelerate to subrelativistic flow on the kiloparsec scale. On the other hand it is shown that beaming of the optical continuum from the core of Centaurus~A is not necessary to account for the excitation of the emission line filaments in the ISM of this galaxy. Models involving autoionizing shocks produced by the interaction between a low Mach number jet and dense clouds along its path are capable of explaining the morphology of the filaments and the simultaneous high excitation and low excitation lines in their spectra.