A simulation-based analytic model of radio galaxies

TL;DR

This paper presents a semi-analytical model for the evolution of powerful radio galaxies, incorporating insights from numerical simulations to predict their dynamics, spectral evolution, and remnant fractions across different environments and redshifts.

Contribution

It introduces a novel simulation-based analytic model that accounts for non-self-similar growth and environmental effects, improving predictions of radio galaxy evolution and remnant populations.

Findings

The model accurately reproduces observed radio source properties.

Remnant fractions are low at high redshift due to inverse-Compton losses.

Source lifetime distribution influences remnant detection in surveys.

Abstract

I derive and discuss a simple semi-analytical model of the evolution of powerful radio galaxies which is not based on assumptions of self-similar growth, but rather implements some insights about the dynamics and energetics of these systems derived from numerical simulations, and can be applied to arbitrary pressure/density profiles of the host environment. The model can qualitatively and quantitatively reproduce the source dynamics and synchrotron light curves derived from numerical modelling. Approximate corrections for radiative and adiabatic losses allow it to predict the evolution of radio spectral index and of inverse-Compton emission both for active sources and for `remnant' sources after the jet has turned off. Code to implement the model is publicly available. Using a standard model with a light relativistic (electron-positron) jet, sub-equipartition magnetic fields, and a range of realistic group/cluster environments, I simulate populations of sources and show that the model can reproduce the range of properties of powerful radio sources as well as observed trends in the relationship between jet power and radio luminosity, and predicts their dependence on redshift and environment. I show that the distribution of source lifetimes has a significant effect on both the source length distribution and the fraction of remnant sources expected in observations, and so can in principle be constrained by observations. The remnant fraction is expected to be low even at low redshift and low observing frequency due to the rapid luminosity evolution of remnants, and to tend rapidly to zero at high redshift due to inverse-Compton losses.