The cosmic spin of the most massive black holes

TL;DR

This paper models the relationship between black hole spin, accretion rates, and radio luminosity in active galactic nuclei, revealing evolving spin distributions over cosmic time.

Contribution

It introduces a model linking black hole spin and accretion to observed radio luminosity functions, explaining galaxy classifications and their evolution.

Findings

High-excitation galaxies have high accretion rates but low spins.

Low-excitation galaxies exhibit bimodal spin distributions.

Average black hole spin was lower at higher redshifts (~z=1).

Abstract

Under the assumption that jets in active galactic nuclei are powered by accretion and the spin of the central supermassive black hole, we are able to reproduce the radio luminosity functions of high- and low-excitation galaxies. High-excitation galaxies are explained as high-accretion rate but very low spin objects, while low-excitation galaxies have low accretion rates and bimodal spin distributions, with approximately half of the population having maximal spins. At higher redshifts (z~1), the prevalence of high accretion rate objects means the typical spin was lower, while in the present day Universe is dominated by low accretion rate objects, with bimodal spin distributions.