Jet Interaction and the Evolution of Compact Symmetric Radio Sources

Abstract

Readhead et al. have recently proposed that compact symmetric objects (CSOs) evolve into larger double sources many kiloparsecs in extent. They propose a detailed empirical model based on recent VLBI survey data that suggest a non-self-similar evolution with a constant hot-spot advance speed independent of the ambient density. The implications of this observational result are explored via numerical modeling. It is found that pure luminosity evolution with constant lobe advance speed is unlikely on the small scales of the CSOs if any ambient gas density gradients exist. However, the transition from CSO to larger double radio sources may involve a nearly constant advance speed into a medium of decreasing density as suggested by Readhead et al. This result can be reproduced by inclusion of additional physics in non-self-similar flows, namely the losses experienced by the outflowing jet as it interacts with its surroundings. The data of Readhead et al. provide observational evidence that this interaction is an important feature of radio source evolution.