BASS. LII. The Prevalence of Double-peaked Broad Lines at Low Accretion Rates among Hard X-Ray Selected Active Galactic Nuclei
Creators
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Ward, Charlotte1
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Koss, Michael J.2, 3
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Eracleous, Michael1
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Trakhtenbrot, Benny4
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Bauer, Franz E.5
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Caglar, Turgay6, 7
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Harrison, Fiona A.8
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Jana, Arghajit9
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Kakkad, Darshan10
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Magno, Macon6, 11
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Moral-Castro, Ignacio del12
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Mushotzky, Richard13
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Oh, Kyuseok14
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Peca, Alessandro2, 15
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Powell, Meredith C.16
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Ricci, Claudio9, 17
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Rojas, Alejandra18
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Smith, Krista Lynne6
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Stern, Daniel19
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Treister, Ezequiel5
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Urry, C. Megan15
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1.
Pennsylvania State University
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2.
Eureka Scientific
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3.
Space Science Institute
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Tel Aviv University
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5.
University of Tarapacá
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6.
Texas A&M University
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7.
Leiden University
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8.
California Institute of Technology
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9.
Diego Portales University
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University of Hertfordshire
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11.
Australia Telescope National Facility
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12.
Pontificia Universidad Católica de Chile
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13.
University of Maryland, College Park
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14.
Korea Astronomy and Space Science Institute
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15.
Yale University
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16.
Leibniz Institute for Astrophysics Potsdam
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17.
Peking University
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Federico Santa María Technical University
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Jet Propulsion Lab
Abstract
A fraction of active galactic nuclei (AGN) have double-peaked Hα, Hβ, and Mg II broad lines attributed to emission from rotating gas in the accretion disk. Using optical spectroscopy of a flux-limited sample of AGN selected via ultrahard X-rays from the BAT AGN Spectroscopic Survey (BASS), we systematically identify 71 double-peaked emitters (DPEs) among 343 broad-line AGN with redshifts 0.004 < z < 0.297 and X-ray luminosities of 40 < log L_(2-10) KeV (erg s−1) < 45.7, and provide their best-fit accretion disk parameters. We find that ∼21% of X-ray-selected broad-line AGN are DPEs, consistent with rates previously reported for z < 0.2 broad-line AGN selected for strong optical variability in the Zwicky Transient Facility. 11 of 71 DPEs (15%) exhibited a single-peaked Gaussian component to the broad line profile in addition to the double-peaked disk profile. In this sample, DPEs have intrinsically higher masses by ∼0.4 dex and lower Eddington ratios by ∼0.3 dex than other broad-line AGN, and have a preference for elliptical host galaxies, higher X-ray luminosities, and higher [O i] λ6302 to narrow Hα flux ratios than other broad-line AGN. We find that DPEs are not segregated from non-DPE broad-line AGN in the Lbol versus MBH relation or their X-ray to radio luminosity ratios, and do not show a preference for intermediate Seyfert types over Seyfert 1s. We do not find differences in a wide range of multiwavelength properties when comparing DPEs to non-DPE broad-line AGN, including optical and mid-IR variability levels, Wide-field Infrared Survey Explorer colors, αox, the column density of neutral obscuring material NH, and the rate of changing-look events. We discuss the two populations in the context of multicomponent disk-wind models of the AGN broad-line region and consider how unrecognized contributions of disk emission to the broad lines may introduce biases in “virial” supermassive black hole mass estimates, with consequences for the inferred MBH–M* relation.
Copyright and License
© 2025. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Acknowledgement
We would like to thank the anonymous referee for their helpful comments. We acknowledge support from NASA through ADAP award 80NSSC22K1126 (M.K.), ANID Fondecyt Regular grants 1230345 (CR),1241005, and 1250821 (F.E.B., E.T.), ANID BASAL project FB210003 (C.R., F.E.B., E.T.), Millennium Science Initiative—AIM23-0001 and ICN12_009 (F.E.B.), and the China-Chile joint research fund (CR). B.T. acknowledges support from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement number 950533). I.M.C. acknowledges support from ANID program FONDECYT Postdoctorado 3230653. K.O. acknowledges support from the Korea Astronomy and Space Science Institute under the R&D program (Project No. 2025-1-831-01), supervised by the Korea AeroSpace Administration, and the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (RS-2025-00553982). A.J. acknowledges support from the FONDECYT Postdoctoral fellowship 3230303.
This research has made use of the CIRADA cutout service,26 operated by the Canadian Initiative for Radio Astronomy Data Analysis (CIRADA). CIRADA is funded by a grant from the Canada Foundation for Innovation 2017 Innovation Fund (Project 35999), as well as by the Provinces of Ontario, British Columbia, Alberta, Manitoba, and Quebec, in collaboration with the National Research Council of Canada, the US National Radio Astronomy Observatory, and Australia’s Commonwealth Scientific and Industrial Research Organization.
This publication also makes use of data products from NEOWISE, which is a project of the Jet Propulsion Laboratory/California Institute of Technology, funded by the Planetary Science Division of the National Aeronautics and Space Administration.
This research has made use of the NASA/IPAC Infrared Science Archive, which is funded by the National Aeronautics and Space Administration and operated by the California Institute of Technology.
Software References
astropy (Astropy Collaboration et al. 2013, 2018, 2022), pPXF (M. Cappellari 2017), SciPy (P. Virtanen et al. 2020).
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Additional details
Additional titles
- Alternative title
- BASS LII: Clues from Twin Peaks -- Investigating the structure of the AGN broad-line region at low accretion rates with double-peaked emitters
Related works
- Is new version of
- Discussion Paper: arXiv:2507.05380 (arXiv)
Funding
- National Aeronautics and Space Administration
- 80NSSC22K1126
- Agencia Nacional de Investigación y Desarrollo
- 1230345
- Agencia Nacional de Investigación y Desarrollo
- 1241005
- Agencia Nacional de Investigación y Desarrollo
- 1250821
- Agencia Nacional de Investigación y Desarrollo
- FB210003
- Millennium Science Initiative
- AIM23-0001
- Millennium Science Initiative
- ICN12_009
- Chinese Academy of Science South America Center for Astronomy
- European Research Council
- 950533
- Fondo Nacional de Desarrollo Científico y Tecnológico
- 3230653
- Korea Astronomy and Space Science Institute
- 2025-1-831-01
- National Research Foundation of Korea
- Ministry of Science and ICT
- RS-2025-00553982
- Fondo Nacional de Desarrollo Científico y Tecnológico
- 3230303
Dates
- Accepted
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2025-07-28
- Available
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2025-09-19Published online