Kavli Affiliate: Claudio Ricci
| First 5 Authors: , , , ,
| Summary:
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
Swift/BAT. Our sample comprises 21 X-ray luminous (log $L_X/rm
erg,s^-1>44.6$, 2-10 keV) AGNs at $z<0.6$, optically classified as Seyfert
1.9-2. Using NuSTAR, XMM-Newton, Suzaku, and Chandra, we constrain AGN
properties such as absorption column density $N_H$, photon index $Gamma$,
intrinsic $L_X$, covering factor, and iron K$alpha$ equivalent width. For
sources with black hole mass estimates (12/20), we find a weak correlation
between $Gamma$ and Eddington ratio ($lambda_Edd$). Of these, six
($50pm13%$) lie in the $N_H$-$lambda_Edd$ "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 spectra,
$82^+6_-16%$ exhibit variability in either 2-10 keV flux
($73^+9_-16%$) or line-of-sight $N_H$ ($33^+15_-10%$). For the 20/21
sources with available near-UV/optical spectroscopy, we detect
[NeV]$lambda$3426 in 17 ($85^+5_-11%$), confirming its reliability to
probe AGN emission even in heavily obscured systems. When normalized to the
same [OIII]$lambda$5007 peak flux as $z = 2$-$9$ narrow-line AGNs identified
with JWST, our sample exhibits significantly stronger [NeV]$lambda$3426
emission, suggesting that high-redshift obscured AGNs may be intrinsically
weaker in [NeV]$lambda$3426 or that [NeV]$lambda$3426 is more challenging to
detect in those environments. The sources presented here serve as a benchmark
for high-redshift analogs, showing the potential of [NeV]$lambda$3426 to
reveal obscured AGNs and the need for future missions to expand X-ray studies
into the high-redshift Universe.
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