An Iwasawa-Taniguchi Effect for Compton-thick Active Galactic Nuclei
Abstract
We present the first study of an Iwasawa–Taniguchi/'X-ray Baldwin' effect for Compton-thick active galactic nuclei (AGN). We report a statistically significant anticorrelation between the rest-frame equivalent width (EW) of the narrow core of the neutral Fe Kα fluorescence emission line, ubiquitously observed in the reflection spectra of obscured AGN, and the mid-infrared 12μm continuum luminosity (taken as a proxy for the bolometric AGN luminosity). Our sample consists of 72 Compton-thick AGN selected from pointed and deep-field observations covering a redshift range of z ∼ 0.0014−3.7. We employ a Monte Carlo-based fitting method, which returns a Spearman's Rank correlation coefficient of ρ = − 0.28 ± 0.12, significant to 98.7 per cent confidence. The best-fitting found is log(EW_(FeKα)) ∝ −0.08 ± 0.04log(L_(12μm)), which is consistent with multiple studies of the X-ray Baldwin effect for unobscured and mildly obscured AGN. This is an unexpected result, as the Fe Kα line is conventionally thought to originate from the same region as the underlying reflection continuum, which together constitute the reflection spectrum. We discuss the implications this could have if confirmed on larger samples, including a systematic underestimation of the line-of-sight X-ray obscuring column density and hence the intrinsic luminosities and growth rates for the most luminous AGN.
Additional Information
© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices) Accepted 2018 March 29. Received 2018 March 29; in original form 2017 September 28. We thank the anonymous referee for invaluable comments on the paper. P. B. and P. G. (grant reference ST/J003697/2) thank the STFC for support. In addition, the authors thank R. Gilli and C. Circosta for providing the 4 and 7 Msspectra of LESS J0033229.4-275619 used in Fig. 2. This work was supported in part by the Black Hole Initiative at Harvard University, which is funded by a grant from the John Templeton Foundation. M. B. acknowledges support from NASA Headquarters under the NASA Earth and Space Science Fellowship Program, grant NNX14AQ07H. We acknowledge financial support from FONDECYT 1141218 (C. R.), Basal-CATA PFB–06/2007 (C. R.), the China-CONICYT fund (C. R.). This work is partly sponsored by the Chinese Academy of Sciences (CAS), through a grant to the CAS South America Center for Astronomy (CASSACA) in Santiago, Chile. The scientific results reported in this article are based on observations made by the Chandra X-ray Observatory. This research has made use of data, software and/or web tools obtained from the High Energy Astrophysics Science Archive Research Center (HEASARC), a service of the Astrophysics Science Division at NASA/GSFC and of the Smithsonian Astrophysical Observatory's High Energy Astrophysics Division. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This work made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. We thank the NuSTAR Operations, Software and Calibration teams for support with the execution and analysis of these observations. This research has made use of the NuSTAR Data Analysis Software (NUSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA). This work is based [in part] on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. This work made use of the NUMPY (Van Der Walt, Colbert & Varoquaux 2011), MATPLOTLIB (Hunter 2007), SCIPY(Jones et al. 2001), PANDAS (McKinney2010), ASTROPY (Astropy Collaboration 2013) and ADJUSTTEXT12 Python packages. P. B. would also like to thank S. Hönig, C. Knigge, J. Matthews, M. Middleton, M. Smith, A. Beri, A. Hill, J. Buchner and others for vital scientific discussions into the data analysis and interpretations of the Compton-thick Iwasawa-Taniguchi effect.Attached Files
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Accepted Version - 1804.01100
Supplemental Material - sty861_supp.pdf
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Additional details
- Eprint ID
- 87283
- Resolver ID
- CaltechAUTHORS:20180620-160311395
- ST/J003697/2
- Science and Technology Facilities Council (STFC)
- John Templeton Foundation
- NNX14AQ07H
- NASA Earth and Space Science Fellowship
- 1141218
- Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)
- PFB–06/2007
- Basal-CATA
- China-CONICYT fund
- Comisión Nacional de Investigación Científica y Tecnológica (CONICYT)
- Chinese Academy of Sciences
- NASA/JPL/Caltech
- Created
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2018-06-21Created from EPrint's datestamp field
- Updated
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2021-11-15Created from EPrint's last_modified field
- Caltech groups
- Infrared Processing and Analysis Center (IPAC), NuSTAR, Astronomy Department