The Radio-Optical Connection in AGN

Summary

Abstract

We review the evidence that ejected radio material plays a fundamental role in the formation and kinematics of the Narrow Line region and the extended emission line regions associated with radio jets in radio galaxies and QSO's. In Seyfert galaxies, the key observation is the existence of high-velocity (several hundred km s⁻¹ from the systemic velocity of the galaxy) emission line components which are found systematically closer to the nucleus that the radio emission peaks. We describe how this result can be explained with a high speed bowshock model. In radio galaxies, the strong shock created by the jet results in a surrounding hot cocoon of gas expanding away from the jet axis. These expanding cocoons are visible in the form of double velocity structure in high resolution optical spectra and have now been detected in 3C120, 3C 171, 3C405 and 3C265. The velocity separation between the components can be as high as several thousand km s⁻¹ We briefly discuss how these cocoons can be used to verify the relativisic beaming hypothesis in systems with strong one-sided jets.

Introduction

Extended emission line regions (EELR) closely aligned with the radio structure have been found in Seyferts [20] and radio galaxies at both low [3] and high redshift [10]. The physical conditions and kinematics of these EELR provide a probe of both the radiation field of the AGN and the role played by ejected material in exciting the emission [13].