Numerical modelling of the lobes of radio galaxies in cluster environments - III. Powerful relativistic and nonrelativistic jets

TL;DR

This study uses relativistic and nonrelativistic simulations to analyze the formation and evolution of radio galaxy lobes in cluster environments, confirming analytical models and revealing magnetic field behaviors.

Contribution

It provides a comprehensive comparison of relativistic and nonrelativistic jet models, validating analytical predictions and exploring magnetic field amplification and orientation in radio lobes.

Findings

Radio lobe widths can be explained by very light jets.

Energy ratio in lobes and ambient gas is consistent across models.

Magnetic field amplification can reach up to twice the initial energy.

Abstract

We present results from two suites of simulations of powerful radio galaxies in poor cluster environments, with a focus on the formation and evolution of the radio lobes. One suite of models uses relativistic hydrodynamics and the other relativistic magnetohydrodynamics; both are set up to cover a range of jet powers and velocities. The dynamics of the lobes are shown to be in good agreement with analytical models and with previous numerical models, confirming in the relativistic regime that the observed widths of radio lobes may be explained if they are driven by very light jets. The ratio of energy stored in the radio lobes to that put into the intracluster gas is seen to be the same regardless of jet power, jet velocity or simulation type, suggesting that we have a robust understanding of the work done on the ambient gas by this type of radio source. For the most powerful jets we at times find magnetic field amplification by up to a factor of two in energy, but mostly the magnetic energy in the lobes is consistent with the magnetic energy injected. We confirm our earlier result that for jets with a toroidally injected magnetic field, the field in the lobes is predominantly aligned with the jet axis once the lobes are well developed, and that this leads to radio flux anisotropies of up to a factor of about two for mature sources. We reproduce the relationship between 151-MHz luminosity and jet power determined analytically in the literature.