Cosmic merger rates and population evolution of binary black hole mergers in AGN disks
Abstract
Active galactic nuclei (AGN) disks are promising sites for hierarchical binary black hole (BBH) mergers, which next-generation gravitational-wave detectors will probe out to high redshift. Predicting their contribution requires linking BBH evolution in AGN disks to the poorly constrained high-redshift evolution of active supermassive black holes (SMBHs). We introduce ARISE (AGN Rates and Intrinsic Stellar-BH Evolution), a framework that embeds semi-analytical models of BBH evolution in AGN disks into a cosmological description of the AGN number density, SMBH mass function, Eddington-ratio distribution, and nuclear metallicity. We consider a conservative AGN-abundance model anchored to observed luminosity functions, as well as Eddington-limited and super-Eddington scenarios based on the CAT cosmological model, compatible with JWST observations of high-redshift AGNs. The merger-rate density is set primarily by the disk viscosity parameter α: at z = 0.2, we find a rate of $12−−37$ Gpc−3 yr−1 for α= 0.01 and $0.5−−6$ Gpc−3 yr−1 for α= 0.1. The redshift evolution depends strongly on how SMBHs grow. The rate density peaks at z ≃ 1.8, $3.3$, and $3.9$ ($1.5$, $3.6$, and $3.9$) for α=0.01 ($0.1$) in the conservative, Eddington-limited, and super-Eddington models, respectively, and in the super-Eddington model it stays nearly flat out to z ≃ 10. For α= 0.1, AGN disks account for ∼ 2--40% of the LVK-inferred merger rate, consistent with current upper limits from GW--AGN associations. For α= 0.01, they match or exceed it. The Einstein Telescope (ET) should detect ∼ 105 (∼ 104) AGN-disk mergers per year for α= 0.01 ($0.1$). ET will test the AGN channel at redshifts where the AGN population models differ most strongly, providing independent constraints on the growth of early SMBHs.
Related
- Detectability of bulk viscosity effects on post-merger gravitational wave signals from binary neutron star mergers
- Simulation Study of Binary Mergers of Galaxy Clusters. I. Properties of Merger Shocks and Radio Emission
- A Possible High-redshift Origin for the Short GRB 061201: Implications of a Compact Binary Merger beyond Cosmic Noon
- The Impact of High-Mass Clusters on the Binary Black Hole Merger Rate over Cosmic Time
- Unifying spatial correlation with hierarchical population inference to constrain the AGN channel for binary black hole mergers
BibTeX
@misc{vaccaro2026cosmic,
title = {{Cosmic merger rates and population evolution of binary black hole mergers in AGN disks}},
author = {Maria Paola Vaccaro and Alessandro Trinca and Michela Mapelli and Lumen Boco and Raffaella Schneider and Rosa Valiante and Dominika Wylezalek},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.40787},
eprint = {2610.40787},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.40787},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Cosmic merger rates and population evolution of binary black hole mergers in AGN disks
AU - Maria Paola Vaccaro
AU - Alessandro Trinca
AU - Michela Mapelli
AU - Lumen Boco
AU - Raffaella Schneider
AU - Rosa Valiante
AU - Dominika Wylezalek
PY - 2026
DA - 2026/10/29
PB - arXiv
DO - 10.48550/arxiv.2610.40787
UR - https://arxiv.org/abs/2610.40787
AB - Active galactic nuclei (AGN) disks are promising sites for hierarchical binary black hole (BBH) mergers, which next-generation gravitational-wave detectors will probe out to high redshift. Predicting their contribution requires linking BBH evolution in AGN disks to the poorly constrained high-redshift evolution of active supermassive black holes (SMBHs). We introduce ARISE (AGN Rates and Intrinsic Stellar-BH Evolution), a framework that embeds semi-analytical models of BBH evolution in AGN disks into a cosmological description of the AGN number density, SMBH mass function, Eddington-ratio distribution, and nuclear metallicity. We consider a conservative AGN-abundance model anchored to observed luminosity functions, as well as Eddington-limited and super-Eddington scenarios based on the CAT cosmological model, compatible with JWST observations of high-redshift AGNs. The merger-rate density is set primarily by the disk viscosity parameter α: at z = 0.2, we find a rate of $12−−37$ Gpc^−3 yr^−1 for α= 0.01 and $0.5−−6$ Gpc^−3 yr^−1 for α= 0.1. The redshift evolution depends strongly on how SMBHs grow. The rate density peaks at z ≃ 1.8, $3.3$, and $3.9$ ($1.5$, $3.6$, and $3.9$) for α=0.01 ($0.1$) in the conservative, Eddington-limited, and super-Eddington models, respectively, and in the super-Eddington model it stays nearly flat out to z ≃ 10. For α= 0.1, AGN disks account for ∼ 2--40% of the LVK-inferred merger rate, consistent with current upper limits from GW--AGN associations. For α= 0.01, they match or exceed it. The Einstein Telescope (ET) should detect ∼ 10^5 (∼ 10^4) AGN-disk mergers per year for α= 0.01 ($0.1$). ET will test the AGN channel at redshifts where the AGN population models differ most strongly, providing independent constraints on the growth of early SMBHs.
ER -