BASS. XXIV. the BASS DR2 Spectroscopic Line Measurements and AGN Demographics

Kyuseok Oh*, Michael J. Koss, Yoshihiro Ueda, Daniel Stern, Claudio Ricci, Benny Trakhtenbrot, Meredith C. Powell, Jakob S. Den Brok, Isabella Lamperti, Richard Mushotzky, Federica Ricci, Rudolf E. Bär, Alejandra F. Rojas, Kohei Ichikawa, Rogério Riffel, Ezequiel Treister, Fiona Harrison, C. Megan Urry, Franz E. Bauer, Kevin Schawinski

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


We present the second catalog and data release of optical spectral line measurements and active galactic nucleus (AGN) demographics of the BAT AGN Spectroscopic Survey, which focuses on the Swift-BAT hard X-ray detected AGNs. We use spectra from dedicated campaigns and publicly available archives to investigate spectral properties of most of the AGNs listed in the 70 month Swift-BAT all-sky catalog; specifically, 743 of the 746 unbeamed and unlensed AGNs (99.6%). We find a good correspondence between the optical emission line widths and the hydrogen column density distributions using the X-ray spectra, with a clear dichotomy of AGN types for N H = 1022 cm-2. Based on optical emission-line diagnostics, we show that 48%-75% of BAT AGNs are classified as Seyfert, depending on the choice of emission lines used in the diagnostics. The fraction of objects with upper limits on line emission varies from 6% to 20%. Roughly 4% of the BAT AGNs have lines too weak to be placed on the most commonly used diagnostic diagram, [O iii]λ5007/Hβ versus [N ii]λ6584/Hα, despite the high signal-to-noise ratio of their spectra. This value increases to 35% in the [O iii]λ5007/[O ii]λ3727 diagram, owing to difficulties in line detection. Compared to optically selected narrow-line AGNs in the Sloan Digital Sky Survey, the BAT narrow-line AGNs have a higher rate of reddening/extinction, with Hα/Hβ > 5 (∼36%), indicating that hard X-ray selection more effectively detects obscured AGNs from the underlying AGN population. Finally, we present a subpopulation of AGNs that feature complex broad lines (34%, 250/743) or double-peaked narrow emission lines (2%, 17/743).

Original languageEnglish
Article number4
JournalAstrophysical Journal, Supplement Series
Issue number1
StatePublished - 1 Jul 2022


FundersFunder number
Eastman Kodak Corporation
Fondecyt Iniciacion11190831
Millennium Nucleus NCN19_058ICN12_009
Samuel Oschin Foundation
National Science FoundationAST-1715512
National Aeronautics and Space Administration20H01946, NNH16CT03C
Alfred P. Sloan Foundation
W. M. Keck Foundation
Office of Science
National Geographic Society
California Institute of Technology
Comunidad de Madrid2018-T1/TIC-11035
Japan Society for the Promotion of ScienceP17321
Fondo Nacional de Desarrollo Científico y Tecnológico3210157
Conselho Nacional de Desenvolvimento Científico e Tecnológico1190818, 1200495
National Research Foundation of KoreaNRF-2020R1C1C1005462
Israel Science Foundation1849/19
Science and Engineering Research Council
Agencia Nacional de Investigación y DesarrolloACT172033, CATA-Basal AFB-170002, FB210003


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