Measuring the properties of active galactic nuclei disks with gravitational waves

TL;DR

This paper develops a phenomenological model for the spin distribution of merging black holes in active galactic nuclei, aiming to distinguish AGN-origin mergers from other channels using gravitational wave data.

Contribution

It introduces a new model for black hole spins in AGN disks, linking model parameters to AGN disk properties and assessing how to differentiate AGN mergers from other sources.

Findings

The model captures unique spin features of AGN mergers.

Future gravitational wave observations can identify AGN as merger sites.

Parameters relate to AGN disk age and density.

Abstract

Active galactic nuclei (AGN) are promising environments for the assembly of merging binary black hole (BBH) systems. Interest in AGNs as nurseries for merging BBH is rising following the detection of gravitational waves from a BBH system from the purported pair-instability mass gap, most notably, GW190521. Active galactic nuclei have also been invoked to explain the formation of the high-mass-ratio system, GW190814. We draw on simulations of BBH systems in AGN to propose a phenomenological model for the distribution of black hole spins of merging binaries in AGN disks. The model incorporates distinct features that make the AGN channel potentially distinguishable from other channels, such as assembly in the field and in globular clusters. The model parameters can be mapped heuristically to the age and density of AGN disks. We estimate the extent to which different populations of mergers in AGNs can be distinguished. If most merging black holes are assembled in AGNs, future gravitational-wave observations may provide insights into the dynamics of AGN disks.