# A representative survey of the dynamics and energetics of FRII radio galaxies

## TL;DR

This study systematically analyzes the dynamics and energetics of FRII radio galaxies, revealing their over-pressured lobes, electron dominance, and strong shocks, and establishes a jet power--radio luminosity relation consistent with theoretical models.

## Contribution

It provides the first large-scale, systematic analysis of FRII radio galaxy energetics and dynamics, including environmental interactions and jet power relations.

## Key findings

- FRII lobes are electron-dominated and over-pressured
- At least half of the radio galaxies drive strong shocks
- Jet power correlates with radio luminosity as predicted by theory

## Abstract

We report the first large, systematic study of the dynamics and energetics of a representative sample of FRII radio galaxies with well-characterized group/cluster environments. We used X-ray inverse-Compton and radio synchrotron measurements to determine the internal radio-lobe conditions, and these were compared with external pressures acting on the lobes, determined from measurements of the thermal X-ray emission of the group/cluster. Consistent with previous work, we found that FRII radio lobes are typically electron-dominated by a small factor relative to equipartition, and are over-pressured relative to the external medium in their outer parts. These results suggest that there is typically no energetically significant proton population in the lobes of FRII radio galaxies (unlike for FRIs), and so for this population, inverse-Compton modelling provides an accurate way of measuring total energy content and estimating jet power. We estimated the distribution of Mach numbers for the population of expanding radio lobes, finding that at least half of the radio galaxies are currently driving strong shocks into their group/cluster environments. Finally, we determined a jet power--radio luminosity relation for FRII radio galaxies based on our estimates of lobe internal energy and Mach number. The slope and normalisation of this relation are consistent with theoretical expectations, given the departure from equipartition and environmental distribution for our sample.