Possible relationship between the radio and optical structures associated with the active galaxy Centaurus A

Abstract

A detailed comparison of the recent deep optical and radio photographs of the nearby radio galaxy Centaurus A (NGC 5128) is presented. This has provided evidence for dynamical interaction between the relativistic plasma and optically detected shell-type structures. Based on this, a new interpretation is suggested for the formation of multiple radio peaks observed in the two giant radio lobes of this active galaxy and also for their inversion symmetric morphology. Also proposed is a method for estimating magnetic field strength inside the radio lobes, based on dynamical considerations of the optical structures interacting with the radio components. The field, thus estimated for the northern inner radio lobe of Cen A, is nearly three times weaker than the value derived under the usual equipartition assumption. The marked bending of the Cen A jet towards this inner radio lobe could be interpreted in terms of what appears to be an encounter with a shell, provided the jet is light and moves with a bulk relativistic speed.