BASS. XLIX. Characterization of Highly Luminous and Obscured AGNs: Local X-Ray and [Ne V]λ3426 Emission in Comparison with the High-redshift Universe

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 ( ${\mathrm{log}}\,{L}_{{\rm{X}}}/{\rm{erg}}\,\,{{\rm{s}}}^{-1}\gt 44.6$ , 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 N _H , photon index Γ, intrinsic L _X , covering factor, and iron K α equivalent width. We find median line-of-sight ${\mathrm{log}}\,{N}_{{\rm{H}}}/{{\rm{cm}}}^{-2}=23.{5}_{-1.2}^{+0.5}$ and 2–10 keV rest-frame, de-absorbed ${\mathrm{log}}\,{L}_{{\rm{X}}}/{\rm{erg}}\,\,{{\rm{s}}}^{-1}=44.{7}_{-0.6}^{+0.8}$ , 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 ( λ _Edd ). Of these, six (50% ± 13%) lie in the N _H - λ _Edd “forbidden region” and exhibit a combined higher prevalence of N _H 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}_{-15}^{+5} \% $ exhibit variability in either 2–10 keV flux ( ${77}_{-15}^{+8} \% $ ) or line-of-sight N _H ( $3{3}_{-10}^{+15} \% $ ). For the 20/21 sources with available near-UV/optical spectroscopy, we detect [Ne v] λ 3426 in 17 ( $8{5}_{-11}^{+5}$ %), confirming its reliability to probe AGN emission even in heavily obscured systems. When renormalized to the same [O iii ] λ 5007 peak flux as z = 2−9 narrow-line AGNs identified with JWST, our sample exhibits significantly stronger [Ne v] λ 3426 emission, suggesting that high-redshift obscured AGNs may be intrinsically weaker in [Ne v] λ 3426 or that [Ne v] λ 3426 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] λ 3426 to reveal obscured AGNs and the need for future missions to expand X-ray studies into the high-redshift Universe.

Keywords

• Active galactic nuclei
• X-ray active galactic nuclei
• X-ray astronomy
• Active galaxies
• High-luminosity active galactic nuclei
• Galaxy evolution