Black hole mergers of AGN origin in LIGO/Virgo's O1-O3a observing periods

TL;DR

This paper investigates the origin of black hole mergers detected by LIGO/Virgo, finding that a significant fraction likely originate from AGN disks, with implications for understanding their mass and spin distributions.

Contribution

It demonstrates that about 25% of observed mergers are better explained by an AGN-disk origin model and estimates the merger rate consistent with theoretical predictions.

Findings

Approximately 25% of events favor an AGN origin over other models.

Estimated AGN merger rate is about 2.8±1.8 Gpc⁻³yr⁻¹.

AGN models can explain high-mass black hole mergers in the pair-instability gap.

Abstract

The origin of the black hole mergers detected by LIGO and Virgo remains an open question. While the unusual mass and spin of a few events constrain their possible astrophysical formation mechanisms, it is difficult to classify the bulk of the observed mergers. Here we consider the distribution of masses and spins in LIGO/Virgo's first and second observing catalogs, and find that for a significant fraction (25%) of these detected events, an AGN-disk origin model is preferred over a parametric mass-spin model fit to the full GWTC-2 merger sample (Bayes factor $\mathcal{B}>10$). We use this to estimate the black hole merger rate in AGNs to be about $2.8\pm 1.8$\, Gpc$^{-3}$yr$^{-1}$, comparable to theoretical expectations. We find that AGNs can explain the rate and mass distribution of the observed events with primary black hole mass in the pair-instability mass gap ($M\gtrsim50$\, M$_\odot$).