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A Growth-rate Indicator for Compton-thick Active Galactic Nuclei

Brightman, M. and Masini, A. and Ballantyne, D. R. and Baloković, M. and Brandt, W. N. and Chen, C.-T. J. and Comastri, A. and Farrah, D. and Gandhi, P. and Harrison, F. A. and Ricci, C. and Stern, D. and Walton, D. J. (2016) A Growth-rate Indicator for Compton-thick Active Galactic Nuclei. Astrophysical Journal, 826 (1). Art. No. 93. ISSN 0004-637X. doi:10.3847/0004-637X/826/1/93.

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Due to their heavily obscured central engines, the growth rate of Compton-thick (CT) active galactic nuclei (AGNs) is difficult to measure. A statistically significant correlation between the Eddington ratio, λ_(Edd), and the X-ray power-law index, Γ, observed in unobscured AGNs offers an estimate of their growth rate from X-ray spectroscopy (albeit with large scatter). However, since X-rays undergo reprocessing by Compton scattering and photoelectric absorption when the line of sight to the central engine is heavily obscured, the recovery of the intrinsic Γ is challenging. Here we study a sample of local, predominantly CT megamaser AGNs, where the black hole mass, and thus Eddington luminosity, are well known. We compile results of the X-ray spectral fitting of these sources with sensitive high-energy (E > 10 keV) NuSTAR data, where X-ray torus models, which take into account the reprocessing effects have been used to recover the intrinsic Γ values and X-ray luminosities, L_X. With a simple bolometric correction to L_X to calculate λ_(Edd), we find a statistically significant correlation between Γ and λ_(Edd) (p = 0.007). A linear fit to the data yields Γ = (0.41 ± 0.18)log_10 λ_(Edd) + (2.38 ± 0.20), which is statistically consistent with results for unobscured AGNs. This result implies that torus modeling successfully recovers the intrinsic AGN parameters. Since the megamasers have low-mass black holes (M_(BH) ≈ 10^6–10^7 M_⊙) and are highly inclined, our results extend the Γ–λ Edd relationship to lower masses and argue against strong orientation effects in the corona, in support of AGN unification. Finally this result supports the use of Γ as a growth-rate indicator for accreting black holes, even for CT AGNs.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Brightman, M.0000-0002-8147-2602
Masini, A.0000-0002-7100-9366
Ballantyne, D. R.0000-0001-8128-6976
Baloković, M.0000-0003-0476-6647
Brandt, W. N.0000-0002-0167-2453
Chen, C.-T. J.0000-0002-4945-5079
Comastri, A.0000-0003-3451-9970
Farrah, D.0000-0003-1748-2010
Gandhi, P.0000-0003-3105-2615
Harrison, F. A.0000-0003-2992-8024
Ricci, C.0000-0001-5231-2645
Stern, D.0000-0003-2686-9241
Walton, D. J.0000-0001-5819-3552
Additional Information:© 2016 The American Astronomical Society. Received 2016 March 31; revised 2016 May 18; accepted 2016 June 11; published 2016 July 25. This work was supported under NASA Contract No. NNG08FD60C, and 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. Furthermore, 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. A.M. and A.C. acknowledge support from the ASI/INAF grant I/037/12/0-011/13. P.G. acknowledges funding from STFC (ST/J003697/2). M.B. acknowledges support from NASA Headquarters under the NASA Earth and Space Science Fellowship Program, grant NNX14AQ07H. Facility: NuSTAR - The NuSTAR (Nuclear Spectroscopic Telescope Array) mission.
Group:NuSTAR, Space Radiation Laboratory
Funding AgencyGrant Number
Agenzia Spaziale Italiana (ASI)I/037/12/0-011/13
Science and Technology Facilities Council (STFC)ST/J003697/2
NASA Earth and Space Science FellowshipNNX14AQ07H
Istituto Nazionale di Astrofisica (INAF)UNSPECIFIED
Subject Keywords:black hole physics; galaxies: general; galaxies: nuclei; galaxies: Seyfert; masers
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory2016-41
Issue or Number:1
Record Number:CaltechAUTHORS:20160802-065750850
Persistent URL:
Official Citation:M. Brightman et al 2016 ApJ 826 93
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:69370
Deposited By: Ruth Sustaita
Deposited On:02 Aug 2016 23:44
Last Modified:11 Nov 2021 04:13

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