The emergence of the X-ray luminosity/cluster richness relation for radio galaxies

TL;DR

This paper investigates the relationship between X-ray luminosity and cluster richness in radio galaxies, proposing a new framework that includes FR0 galaxies and challenges traditional merger-driven models.

Contribution

It introduces a novel interpretation of the X-ray luminosity/cluster richness relation, incorporating FR0 radio galaxies as transition states rather than initial or final phases.

Findings

X-ray luminosity correlates with environmental richness in radio galaxies.

FR0 galaxies are integrated into the evolutionary framework of radio galaxies.

The jet-disk connection underpins the observed luminosity and environment relation.

Abstract

The idea that mergers are more likely in dense groups or clusters coupled with the assumption that such events lead to cold gas flows onto black holes, suggests a direct relationship between the radiative efficiency of an active galactic nucleus and environmental richness. Observations, however, increasingly challenge this and other basic expectations. Mounting evidence, for example, shows an inverse trend between near-Eddington accreting objects and environmental richness. Broken down by radio galaxy subgroup, recent work has explored connections between low excitation radio galaxies with Fanaroff-Riley II jet morphology (FRII LERGs) and other radio galaxies. We make contact with that work by adding a discussion of the recently discovered FR0 radio galaxies and show how to fit them in a picture in which FRII LERGs are not initial nor final phases in the lifetime of a radio galaxy, but de facto transition states. We describe how to understand the observed X-ray luminosity/cluster richness relation as a fundamental correlation on the nature of the jet-disk connection.