Luminosity function, sizes and FR dichotomy of radio-loud AGN

TL;DR

This paper presents an analytical model linking the luminosity, size evolution, and morphological classification of radio-loud AGN, successfully reproducing observed luminosity functions and size distributions, and connecting accretion modes to jet power.

Contribution

It introduces a unified model for FR I and FR II radio galaxy evolution, explaining the luminosity function break and size distribution based on morphological transitions.

Findings

The model reproduces the observed slopes and break luminosity of the RLF.

The rate of AGN with jet power Q scales as Q^{-1.6}.

The size distribution of FRII sources aligns with the model under certain luminosity drop conditions.

Abstract

The radio luminosity function (RLF) of radio galaxies and radio-loud quasars is often modelled as a broken power-law. The break luminosity is close to the dividing line between the two Fanaroff-Riley (FR) morphological classes for the large-scale radio structure of these objects. We use an analytical model for the luminosity and size evolution of FRII-type objects together with a simple prescription for FRI-type sources to construct the RLF. We postulate that all sources start out with an FRII-type morphology. Weaker jets subsequently disrupt within the quasi-constant density cores of their host galaxies and develop turbulent lobes of type FRI. With this model we recover the slopes of the power laws and the break luminosity of the RLF determined from observations. The rate at which AGN with jets of jet power $Q$ appear in the universe is found to be proportional to $Q^{-1.6}$. The model also roughly predicts the distribution of the radio lobe sizes for FRII-type objects, if the radio luminosity of the turbulent jets drops significantly at the point of disruption. We show that our model is consistent with recent ideas of two distinct accretion modes in jet-producing AGN, if radiative efficiency of the accretion process is correlated with jet power.