A model for the surface brightness of a turbulent, low Mach number jet. II - The global energy budget and radiative losses

Abstract

Detailed consideration is given to the energy balance in extragalactic radio sources, in particular the Fanaroff-Riley class I radio sources whose morphology is likely to be due to jets being stopped by entrainment of the surrounding medium. Two important features of the energy balance are the demonstration that, given the fractional composition of the plasma in relativistic electrons, the ratio of lobe luminosity to jet energy flux, κ, can be estimated from observational parameters and that in low Mach number sources the jet energy flux is dominated by the enthalpy flux. The parameter κ depends upon the ratio Ee/EL of relativistic electron energy to total lobe energy and it is likely that this is determined by the initial composition of plasma ejected from the core and the amount of entrained nonrelativistic material. Spectral index variations in jets of arbitrary velocity are also considered since this provides a means of determining whether a jet is dissipative over a given region or not. The theoretical results are applied to analyze further the class I source 3C 31.