The Evolution of Radio Loud Active Galactic Nuclei as a Function of Black Hole Spin

TL;DR

This paper investigates how black hole spin evolution influences the radio loudness of active galactic nuclei, proposing a model where spin changes from retrograde to prograde over cosmic time, affecting jet power and spectral features.

Contribution

It introduces a model linking black hole spin evolution to radio-loudness, explaining spectral differences and the distribution of jet power across cosmic history.

Findings

Radio-loud quasars have retrograde spinning black holes.

Radio-quiet objects host prograde spinning black holes.

Jet power decreases due to fewer retrograde accretion systems at lower redshift.

Abstract

Recent work on the engines of active galactic nuclei jets suggests their power depends strongly and perhaps counter-intuitively on black hole spin. We explore the consequences of this on the radio-loud population of active galactic nuclei and find that the time evolution of the most powerful radio galaxies and radio-loud quasars fits into a picture in which black hole spin varies from retrograde to prograde with respect to the accreting material. Unlike the current view, according to which jet powers decrease in tandem with a global downsizing effect, we argue for a drop in jet power resulting directly from the paucity of retrograde accretion systems at lower redshift $z$ caused by a continuous history of accretion dating back to higher $z$. In addition, the model provides simple interpretations for the basic spectral features differentiating radio-loud and radio-quiet objects, such as the presence or absence of disk reflection, broadened iron lines and signatures of disk winds. We also briefly describe our models' interpretation of microquasar state transitions. We highlight our result that the most radio-loud and most radio-quiet objects both harbor highly spinning black holes but in retrograde and prograde configurations, respectively.