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NuSTAR Observations of AGNs with Low Observed X-Ray to [O III] Luminosity Ratios: Heavily Obscured AGNs or Turned-off AGNs?

Saade, M. Lynne and Brightman, Murray and Stern, Daniel and Malkan, Matthew A. and García, Javier A. (2022) NuSTAR Observations of AGNs with Low Observed X-Ray to [O III] Luminosity Ratios: Heavily Obscured AGNs or Turned-off AGNs? Astrophysical Journal, 936 (2). Art. No. 162. ISSN 0004-637X. doi:10.3847/1538-4357/ac88cf.

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Type 2 active galactic nuclei (AGNs) show signatures of accretion onto a supermassive black hole through strong, high-ionization, narrow emission lines extended on scales of hundreds to thousands of parsecs, but they lack the broad emission lines from close in to the black hole that characterize type 1 AGNs. The lack of broad emission could indicate obscuration of the innermost nuclear regions, or could indicate that the black hole is no longer strongly accreting. Since high-energy X-rays can penetrate thick obscuring columns, they have the power to distinguish these two scenarios. We present high-energy NuSTAR observations of nine Seyfert 2 AGNs from the Infrared Astronomical Satellite 12 μm survey, supplemented with low-energy X-ray observations from Chandra, XMM-Newton, and Swift. The galaxies were selected to have anomalously low observed 2–10 keV luminosities compared to their [O III] optical luminosities, a traditional diagnostic of heavily obscured AGNs, reaching into the Compton-thick regime for the highest hydrogen column densities (N_H > 1.5 × 10²⁴ cm⁻²). Based on updated [O III] luminosities and intrinsic X-ray luminosities based on physical modeling of the hard X-ray spectra, we find that one galaxy was misclassified as type 2 (NGC 5005) and most of the remaining AGNs are obscured, including three confirmed as Compton thick (IC 3639, NGC 1386, and NGC 3982). One galaxy, NGC 3627, appears to have recently deactivated. Compared to the original sample that the nine AGNs were selected from, this is a rate of approximately 1%. We also find a new X-ray changing-look AGN in NGC 6890.

Item Type:Article
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URLURL TypeDescription
Saade, M. Lynne0000-0001-7163-7015
Brightman, Murray0000-0002-8147-2602
Stern, Daniel0000-0003-2686-9241
Malkan, Matthew A.0000-0001-6919-1237
García, Javier A.0000-0003-3828-2448
Additional Information:The scientific results reported in this article are based on data obtained from the Chandra Data Archive. This work is based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. We acknowledge the use of public data from the Swift data archive. This research has made use of data and/or software provided by the High Energy Astrophysics Science Archive Research Center (HEASARC), which is a service of the Astrophysics Science Division at NASA/GSFC and the High Energy Astrophysics Division of the Smithsonian Astrophysical Observatory. This work has made use of data obtained from the NuSTAR mission, a project led by Caltech, funded by NASA and managed by NASA/JPL. M.L.S. would like to thank Lisbeth D. Jensen for her help in digging through the data used in Malkan et al. (2017), and Donaji Esparza-Arredondo for showing her the fitting results for NGC 3627 from Esparza-Arredondo et al. (2020). J.A.G. acknowledges support from NASA grant 80NSSC21K1567 and from the Alexander von Humboldt Foundation.
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Alexander von Humboldt FoundationUNSPECIFIED
Issue or Number:2
Record Number:CaltechAUTHORS:20220919-280781900
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:117074
Deposited By: Melissa Ray
Deposited On:21 Sep 2022 22:20
Last Modified:21 Sep 2022 22:20

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