BASS. XLIX. Characterization of Highly Luminous and Obscured AGNs: Local X-Ray and [Ne V]λ3426 Emission in Comparison with the High-redshift Universe
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Date
2025
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Abstract
We present a detailed analysis of the most luminous and obscured active galactic nuclei (AGNs) detected in the ultra-hard X-ray band (14–195 kev) by the Swift/Burst Alert Telescope. Our sample comprises 21 X-ray luminous (log LX/erg s > 44.6 1 , 2–10 keV) AGNs at z < 0.6, optically classified as Seyfert 1.9 and 2. Using NuSTAR, XMM-Newton, Suzaku, and Chandra data, we constrain AGN properties such as absorption column density NH, photon index Γ, intrinsic LX, covering factor, and iron Kα equivalent width. We find median line-ofsight / = + logNH cm 23.5 2 1.2 0.5 and 2–10 keV rest-frame, de-absorbed / = + log LX erg s 44.7 1 0.6 0.8, at the 5th and 95th percentiles. For sources with black hole mass estimates (12/20), we find a weak correlation between Γ and Eddington ratio (λEdd). Of these, six (50% ± 13%) lie in the NH-λEdd “forbidden region” and exhibit a combined higher prevalence of NH variability and outflow signatures, suggesting a transitional phase where AGN feedback may be clearing the obscuring material. For the 13/21 sources with multi-epoch X-ray spectroscopy, + 85 1 5 5% exhibit variability in either 2–10 keV flux (+ 77 1 8 5%) or line-of-sight NH (+ 33 1 1 0 5% ). For the 20/21 sources with available near-UV/optical spectroscopy, we detect [Ne v]λ3426 in 17 (+ 85 11 5 %), confirming its reliability to probe AGN emission even in heavily obscured systems. When renormalized to the same [O III]λ5007 peak flux as z = 2 −9 narrow-line AGNs identified with JWST, our sample exhibits significantly stronger [Ne v]λ3426 emission, suggesting that high-redshift obscured AGNs may be intrinsically weaker in [Ne v]λ3426 or that [Ne v]λ3426 is more challenging to detect in those environments. The sources presented in this work serve as a benchmark for high-redshift analogs, showing the potential of [Ne v]λ3426 to reveal obscured AGNs and the need for future missions to expand X-ray studies into the high-redshift Universe.
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Keywords
Active galactic nuclei, X-ray active galactic nuclei, X-ray astronomy, Active galaxies, High-luminosity active galactic nuclei, Galaxy evolution, High energy astrophysics, High-redshift galaxies, James Webb Space Telescope, Seyfert galaxies