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

Author:

Oh KyuseokORCID,Koss Michael J.ORCID,Ueda YoshihiroORCID,Stern DanielORCID,Ricci ClaudioORCID,Trakhtenbrot BennyORCID,Powell Meredith C.ORCID,den Brok Jakob S.ORCID,Lamperti IsabellaORCID,Mushotzky RichardORCID,Ricci FedericaORCID,Bär Rudolf E.ORCID,Rojas Alejandra F.ORCID,Ichikawa KoheiORCID,Riffel RogérioORCID,Treister EzequielORCID,Harrison Fiona,Urry C. MeganORCID,Bauer Franz E.ORCID,Schawinski KevinORCID

Abstract

Abstract 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).

Funder

National Research Foundation of Korea

Publisher

American Astronomical Society

Subject

Space and Planetary Science,Astronomy and Astrophysics

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