Parsec-Scale Jet-Environment Interactions in AGN

TL;DR

This review discusses how radio jets in AGN evolve from parsec to hundreds of kiloparsecs, emphasizing the roles of jet-environment interactions and intermittent fueling, supported by VLBA observations and hydrodynamical simulations.

Contribution

It synthesizes current observational and simulation evidence to evaluate the impact of environment and fueling on AGN jet evolution, highlighting the dominance of intermittent accretion.

Findings

Dense environments can temporarily hinder jets but not stop them.

VLBA studies show collimated outflows in dense environments.

Intermittent accretion likely drives AGN jet evolution.

Abstract

Observations made with the VLBA have led to fundamental advances in our understanding of how radio jets in AGN evolve from parsec-scales out to distances exceeding several hundred kiloparsecs. In this review I discuss current models of young radio source evolution, as well as the observational evidence for a rapid change in jet properties on scales of ~1 kpc. A central topic of current debate is the relative importance of intermittent jet fueling versus jet-environment interactions in causing a drop-off in powerful radio sources at this critical evolutionary stage. Recent 3-D hydrodynamical jet simulations suggest that dense environments and cloud collisions can temporarily stifle, but not completely halt powerful relativistic jets. Several VLBA studies of jet-ISM interactions in both blazars and weak Seyfert jets have indicated that collimated outflows are indeed possible in dense environments. At present, the bulk of the evidence favors intermittent AGN accretion as the dominant factor in determining the evolutionary path of large numbers of AGN jets.