# Monte-Carlo simulations of black hole mergers in AGN disks: Low $\chi_{\rm eff}$ mergers and predictions for LIGO

## TL;DR

This study uses Monte-Carlo simulations to explore black hole mergers in AGN disks, predicting low effective spin parameters and specific mass distributions, with implications for LIGO observations and AGN disk properties.

## Contribution

It provides new insights into the spin and mass distributions of black hole mergers in AGN disks, highlighting the role of migration traps and constraints from LIGO non-detections.

## Key findings

- $ ilde{
m ext{eff}}$ centered around 0.0
- Mass ratios $ ilde{q} ext{~} 0.5-0.7$
- Maximum merger mass $ ext{~} 100-200 M_{
m ext{sun}}$

## Abstract

Accretion disks around supermassive black holes are promising sites for stellar mass black hole mergers detectable with LIGO. Here we present the results of Monte-Carlo simulations of black hole mergers within 1-d AGN disk models. For the spin distribution in the disk bulk, key findings are: (1) The distribution of $\chi_{\rm eff}$ is naturally centered around $\tilde{\chi}_{\rm eff} \approx 0.0$, (2) the width of the $\chi_{\rm eff}$ distribution is narrow for low natal spins. For the mass distribution in the disk bulk, key findings are: (3) mass ratios $\tilde{q} \sim 0.5-0.7$, (4) the maximum merger mass in the bulk is $\sim 100-200M_{\odot}$, (5) $\sim 1\%$ of bulk mergers involve BH $>50M_{\odot}$ with (6) $\simeq 80\%$ of bulk mergers are pairs of 1st generation BH. Additionally, mergers at a migration trap grow an IMBH with typical merger mass ratios $\tilde{q}\sim 0.1$. Ongoing LIGO non-detections of black holes $>10^{2}M_{\odot}$ puts strong limits on the presence of migration traps in AGN disks (and therefore AGN disk density and structure) as well as median AGN disk lifetime. The highest merger rate occurs for this channel if AGN disks are relatively short-lived ($\leq 1$Myr) so multiple AGN episodes can happen per Galactic nucleus in a Hubble time.