A Simulation Study of Ultra-relativistic Jets -- II. Structures and Dynamics of FR-II Jets

TL;DR

This study uses advanced 3D relativistic hydrodynamic simulations to analyze the structures, dynamics, and energy dissipation mechanisms of FR-II radio galaxy jets, revealing how jet power influences morphology and turbulence.

Contribution

It introduces a high-order accurate RHD simulation code with realistic physics to systematically explore jet structures and energy dissipation in FR-II jets, highlighting the role of jet power.

Findings

Jet morphology depends mainly on jet power.

Higher power jets are faster and more elongated.

Energy dissipation varies with jet power and flow dynamics.

Abstract

We study the structures of ultra-relativistic jets injected into the intracluster medium (ICM) and the associated flow dynamics, such as shocks, velocity shear, and turbulence, through three-dimensional relativistic hydrodynamic (RHD) simulations. To that end, we have developed a high-order accurate RHD code, equipped with a weighted essentially non-oscillatory (WENO) scheme and a realistic equation of state (Seo et al. 2021, Paper I). Using the code, we explore a set of jet models with the parameters relevant to FR-II radio galaxies. We confirm that the overall jet morphology is primarily determined by the jet power, and the jet-to-background density and pressure ratios play secondary roles. Jets with higher powers propagate faster, resulting in more elongated structures, while those with lower powers produce more extended cocoons. Shear interfaces in the jet are dynamically unstable, and hence, chaotic structures with shocks and turbulence develop. We find that the fraction of the jet-injected energy dissipated through shocks and turbulence is greater in less powerful jets, although the actual amount of the dissipated energy is larger in more powerful jets. In lower power jets, the backflow is dominant in the energy dissipation owing to the broad cocoon filled with shocks and turbulence. In higher power jets, by contrast, both the backflow and jet spine flow are important for the energy dissipation. Our results imply that different mechanisms, such as diffusive shock acceleration, shear acceleration, and stochastic turbulent acceleration, may be involved in the production of ultra-high energy cosmic rays in FR-II radio galaxies.