Published in The Astronomy and Astrophysics Review, Volume 24, Issue 1, article id.10, 59 pp, 2016.
https://arxiv.org/abs/1605.08773

For a PDF version of the article, click here.

RADIO AGN IN THE LOCAL UNIVERSE: UNIFICATION, TRIGGERING AND EVOLUTION

Clive Tadhunter


Abstract: Associated with one of the most important forms of active galactic nucleus (AGN) feedback, and showing a strong preference for giant elliptical host galaxies, radio AGN (L1.4 GHz > 1024 W Hz−1) are a key sub-class of the overall AGN population. Recently their study has benefitted dramatically from the availability of high-quality data covering the X-ray to far-IR wavelength range obtained with the current generation of ground- and space-based telescope facilities. Reflecting this progress, here I review our current state of understanding of the population of radio AGN at low and intermediate redshifts (z < 0.7), concentrating on their nuclear AGN and host galaxy properties, and covering three interlocking themes: the classification of radio AGN and its interpretation; the triggering and fuelling of the jet and AGN activity; and the evolution of the host galaxies. I show that much of the observed diversity in the AGN properties of radio AGN can be explained in terms of a combination of orientation/anisotropy, mass accretion rate, and variability effects. The detailed morphologies of the host galaxies are consistent with the triggering of strong line radio galaxies (SLRG) in galaxy mergers. However, the star formation properties and cool ISM contents suggest that the triggering mergers are relatively minor in terms of their gas masses in most cases, and would not lead to major growth of the supermassive black holes and stellar bulges; therefore, apart from a minority (< 20%) that show evidence for higher star formation rates and more massive cool ISM reservoirs, the SLRG represent late-time re-triggering of activity in mature giant elliptical galaxies. In contrast, the host and environmental properties of weak line radio galaxies (WLRG) with Fanaroff-Riley class I (FRI) radio morphologies are consistent with more gradual fuelling of the activity via gas accretion at low rates onto the supermassive black holes.


Keywords: Galaxies:active; Galaxies:jets; Galaxies:evolution


Table of Contents

INTRODUCTION

AGN AND JET PROPERTIES
AClassification
Orientation-based unification I: SLRG
Orientation-based unification II: WLRG
Accretion rates and modes
Variability
Relationship to lower luminosity radio AGN samples

THE HOST GALAXIES AND ENVIRONMENTS OF RADIO AGN
Overall morphologies, light profiles, kinematics and masses
Morphological peculiarities
Star formation
UV/optical diagnostics
Mid-IR diagnostics
Far-IR diagnostics
Star formation summary
Dust and gas contents
Large-scale environments
The triggering of radio AGN

CONCLUSIONS

OUTLOOK

REFERENCES

Next