Eddington ratio and accretion efficiency in AGN evolution

TL;DR

This study explores the evolution of Active Galactic Nuclei (AGN) by including low Eddington ratio objects, revealing multiple AGN populations and emphasizing the importance of variable accretion efficiency and black hole spin in their evolution.

Contribution

It introduces an evolution model incorporating low Eddington ratio AGN and demonstrates the existence of multiple evolving populations consistent with local black hole mass functions.

Findings

Three distinct AGN populations can evolve within a wider parameter range.

Black holes in the models are generally rapidly spinning.

Fixed accretion efficiency and Eddington ratio do not fully explain AGN evolution.

Abstract

The cosmological evolution of Active Galactic Nuclei (AGN) is important for understanding the mechanism of accretion onto supermassive black holes, and the related evolution of the host galaxy. In this work, we include objects with very low Eddington ratio (10^{-3} - 10^{-2}) in an evolution scenario, and compare the results with the observed local distribution of black holes. We test several possibilities for the AGN population, considering obscuration and dependence with luminosity, and investigate the role of the Eddington ratio and radiative accretion efficiency on the shape of the evolved mass function. We find that three distinct populations of AGN can evolve with a wider parameter range than is usually considered, and still be consistent with the local mass function. In general, the black holes in our solutions are spinning rapidly. Taking fixed values for accretion efficiency and Eddington ratio neither provides a full knowledge of the evolution mechanism nor is consistent with the existence of low Eddington ratio objects.