---
OA_place: repository
OA_type: green
_id: '19497'
abstract:
- lang: eng
  text: The stochastic gravitational wave (GW) background recently discovered by several
    pulsar timing array experiments is consistent with arising from a population of
    coalescing super-massive black hole binaries. The amplitude of the background
    is somewhat higher than expected in most previous population models or from the
    local mass density observations. Such binaries are expected to be produced in
    galaxy mergers, which are also thought to trigger bright quasar activity. Under
    the assumptions that (i) a fraction fbin∼1 of all quasars are associated with
    mergers, (ii) the typical quasar lifetime is tQ∼108 yr, and (iii) adopting Eddington
    ratios fEdd∼0.25 for the luminosity of quasars, we compute the GW background associated
    directly with the empirically measured quasar luminosity function. This approach
    bypasses the need to model the cosmological evolution of black holes or galaxy
    mergers from simulations or semi-analytical models. We find the amplitude matching
    the value measured by NANOGrav. Our results are consistent with most quasars being
    associated with black hole binaries and being the sources of the GW background,
    and imply a joint constraint on tQ, fEdd and the typical mass ratio q≡M2/M1. The
    signal in this case would be dominated by relatively distant ∼109M⊙ sources at
    z≈2−3, at the peak of quasar activity. Similarly to other models, our results
    remain in tension with the local super-massive black hole mass density.
acknowledgement: We thank Chengcheng Xin and Girish Kulkarni for useful discussions.
  ZH gratefully acknowledges the hospitality of Eötvös University during an extended
  sabbatical visit, where this work began. ZH acknowledges support from NSF Grant
  AST-2006176 and NASA Grants 80NSSC22K0822 and 80NSSC24K0440. ZF acknowledges support
  from the Hungarian National Research, Development and Innovation Office (NKFIH)
  through the Institutional Excellence Program No. TKP2021-NKTA-64.
article_number: '075007'
article_processing_charge: No
article_type: original
arxiv: 1
author:
- first_name: Ágnes
  full_name: Kis-Tóth, Ágnes
  last_name: Kis-Tóth
- first_name: Zoltán
  full_name: Haiman, Zoltán
  id: 7c006e8c-cc0d-11ee-8322-cb904ef76f36
  last_name: Haiman
  orcid: 0000-0003-3633-5403
- first_name: Zsolt
  full_name: Frei, Zsolt
  last_name: Frei
citation:
  ama: Kis-Tóth Á, Haiman Z, Frei Z. Can quasars, triggered by mergers, account for
    NANOGrav’s stochastic gravitational wave background? <i>Classical and Quantum
    Gravity</i>. 2025;42(7). doi:<a href="https://doi.org/10.1088/1361-6382/adbda6">10.1088/1361-6382/adbda6</a>
  apa: Kis-Tóth, Á., Haiman, Z., &#38; Frei, Z. (2025). Can quasars, triggered by
    mergers, account for NANOGrav’s stochastic gravitational wave background? <i>Classical
    and Quantum Gravity</i>. IOP Publishing. <a href="https://doi.org/10.1088/1361-6382/adbda6">https://doi.org/10.1088/1361-6382/adbda6</a>
  chicago: Kis-Tóth, Ágnes, Zoltán Haiman, and Zsolt Frei. “Can Quasars, Triggered
    by Mergers, Account for NANOGrav’s Stochastic Gravitational Wave Background?”
    <i>Classical and Quantum Gravity</i>. IOP Publishing, 2025. <a href="https://doi.org/10.1088/1361-6382/adbda6">https://doi.org/10.1088/1361-6382/adbda6</a>.
  ieee: Á. Kis-Tóth, Z. Haiman, and Z. Frei, “Can quasars, triggered by mergers, account
    for NANOGrav’s stochastic gravitational wave background?,” <i>Classical and Quantum
    Gravity</i>, vol. 42, no. 7. IOP Publishing, 2025.
  ista: Kis-Tóth Á, Haiman Z, Frei Z. 2025. Can quasars, triggered by mergers, account
    for NANOGrav’s stochastic gravitational wave background? Classical and Quantum
    Gravity. 42(7), 075007.
  mla: Kis-Tóth, Ágnes, et al. “Can Quasars, Triggered by Mergers, Account for NANOGrav’s
    Stochastic Gravitational Wave Background?” <i>Classical and Quantum Gravity</i>,
    vol. 42, no. 7, 075007, IOP Publishing, 2025, doi:<a href="https://doi.org/10.1088/1361-6382/adbda6">10.1088/1361-6382/adbda6</a>.
  short: Á. Kis-Tóth, Z. Haiman, Z. Frei, Classical and Quantum Gravity 42 (2025).
date_created: 2025-04-06T22:01:32Z
date_published: 2025-04-04T00:00:00Z
date_updated: 2025-09-30T11:30:11Z
day: '04'
department:
- _id: ZoHa
doi: 10.1088/1361-6382/adbda6
external_id:
  arxiv:
  - '2412.12726'
  isi:
  - '001448904700001'
intvolume: '        42'
isi: 1
issue: '7'
language:
- iso: eng
main_file_link:
- open_access: '1'
  url: https://doi.org/10.48550/arXiv.2412.12726
month: '04'
oa: 1
oa_version: Preprint
publication: Classical and Quantum Gravity
publication_identifier:
  eissn:
  - 1361-6382
  issn:
  - 0264-9381
publication_status: published
publisher: IOP Publishing
quality_controlled: '1'
scopus_import: '1'
status: public
title: Can quasars, triggered by mergers, account for NANOGrav’s stochastic gravitational
  wave background?
type: journal_article
user_id: 317138e5-6ab7-11ef-aa6d-ffef3953e345
volume: 42
year: '2025'
...