McFacts III: Compact binary mergers from AGN disks over an entire synthetic universe

TL;DR

This paper models the contribution of AGN disks to the population of binary black hole mergers, predicting observable events and their galaxy host properties, and assessing the impact of AGN lifetime assumptions.

Contribution

It extends previous work by integrating galaxy properties and cosmological models to predict BBH merger populations from AGN disks across an entire universe.

Findings

AGN disks may explain massive BBH mergers like GW190521.

Most observable mergers originate in galaxies with supermassive black holes between 10^7 and 10^9.4 solar masses.

AGN lifetime of 0.5 to 2.5 Myr is needed if hierarchical mergers are significant.

Abstract

The Active Galactic Nuclei (AGN) channel for the formation of binary black hole (BBH) mergers has been previously studied as a potential formation channel for the merging compact binaries observed by the LIGO/Virgo/KAGRA (LVK) scientific collaboration. The first two papers in this series explored the McFACTS code for the evolution of black hole orbits in AGN accretion disks for individual galaxy models and described the characteristics of predicted BBH populations in realizations of those models (such as the correlation between mass ratio and aligned spin). In this work, we explore the impact of the properties of AGN host galaxies and assume an AGN lifetime and cosmological model for the density of AGN in a universe like our own. By sampling from an inferred population of AGN, we marginalize over galaxy mass to predict a population of BBH mergers observable by modern ground-based gravitational wave observatories. We find that for reasonable assumptions, AGN disk environments may account for massive BBH mergers such as GW190521 and GW190929_012149. We find that the majority of observable BBH mergers from our simulation are expected to originate in galaxies with a super-massive black hole between $10^{7}M_{\odot}$ and $10^{9.4}M_{\odot}$. We also find that if hierarchical mergers from AGN disks account for a substantial part of the LVK population, our current models require an AGN lifetime of 0.5 to 2.5 Myr.