The use of radio observations to constrain the luminosity of an anisotropic radiation field in radio galaxies

Abstract

The properties of radio bridges may be used to constrain the luminosity of anisotropic radiation emitted by the AGN in radio galaxies, assuming that the emission axis of the radiation is close to that of the jet that powers the radio lobes. This constraint is derived and applied to a sample of powerful radio galaxies with redshifts of about 1. The total radiant luminosity of the AGN in these galaxies is constrained to be less than about (4h−1 sin α)×1046 erg s−1 for radiation that is emitted into two cones each with an opening angle that lies between about 5° sin α and 60° sin α, where α is the angle between the emission axis and the line of sight to the observer. Most likely, less than about one third of the total radiant luminosity is emitted in the ultraviolet, which implies the interesting bound that in these systems the ultraviolet luminosity is less than about Luv≲(h−1 sin α)×1046 erg s−1.