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A New Population of Compton-thick AGNs Identified Using the Spectral Curvature above 10 keV

Koss, Michael J. and Assef, R. and Baloković, M. and Stern, D. and Gandhi, P. and Lamperti, I. and Alexander, D. M. and Ballantyne, D. R. and Bauer, F. E. and Berney, S. and Brandt, W. N. and Comastri, A. and Gehrels, N. and Harrison, F. A. and Lansbury, G. and Markwardt, C. and Ricci, C. and Rivers, E. and Schawinski, K. and Trakhtenbrot, B. and Treister, E. and Urry, C. Megan (2016) A New Population of Compton-thick AGNs Identified Using the Spectral Curvature above 10 keV. Astrophysical Journal, 825 (2). Art. No. 85. ISSN 0004-637X.

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We present a new metric that uses the spectral curvature (SC) above 10 keV to identify Compton-thick active galactic nuclei (AGNs) in low-quality Swift/Burst Alert Telescope (BAT) X-ray data. Using NuSTAR, we observe nine high SC-selected AGNs. We find that high-sensitivity spectra show that the majority are Compton-thick (78% or 7/9) and the remaining two are nearly Compton-thick (N_H ≃ (5–8) × 10^(23) cm^(−2)). We find that the SC_(BAT) and SC_(NuSTAR) measurements are consistent, suggesting that this technique can be applied to future telescopes. We tested the SC method on well-known Compton-thick AGNs and found that it is much more effective than broadband ratios (e.g., 100% using SC versus 20% using 8–24 keV/3–8 keV). Our results suggest that using the >10 keV emission may be the only way to identify this population since only two sources show Compton-thick levels of excess in the Balmer decrement corrected [O iii] to observed X-ray emission ratio (F_([O III])/f^(obs)_(2-10 kev) > 1) and WISE colors do not identify most of them as AGNs. Based on this small sample, we find that a higher fraction of these AGNs are in the final merger stage (<10 kpc) than typical BAT AGNs. Additionally, these nine obscured AGNs have, on average, ≈4× higher accretion rates than other BAT-detected AGNs (〈λ_(Edd)〉= 0.068 ± 0.023 compared to 〈λ_(Edd)〉= 0.016 ± 0.004). The robustness of SC at identifying Compton-thick AGNs implies that a higher fraction of nearby AGNs may be Compton-thick (≈22%) and the sum of black hole growth in Compton-thick AGNs (Eddington ratio times population percentage) is nearly as large as mildly obscured and unobscured AGNs.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Koss, Michael J.0000-0002-7998-9581
Assef, R.0000-0002-9508-3667
Stern, D.0000-0003-2686-9241
Gandhi, P.0000-0003-3105-2615
Lamperti, I.0000-0003-3336-5498
Alexander, D. M.0000-0002-5896-6313
Ballantyne, D. R.0000-0001-8128-6976
Bauer, F. E.0000-0002-8686-8737
Brandt, W. N.0000-0002-0167-2453
Comastri, A.0000-0003-3451-9970
Harrison, F. A.0000-0003-2992-8024
Lansbury, G.0000-0002-5328-9827
Ricci, C.0000-0001-5231-2645
Urry, C. Megan0000-0002-0745-9792
Additional Information:© 2016 The American Astronomical Society. Received 2015 December 1; revised 2016 March 29; accepted 2016 April 18; published 2016 July 6. We acknowledge financial support from Ambizione fellowship grant PZ00P2_154799/1 (M.K.), the Swiss National Science Foundation (NSF) grant PP00P2 138979/1 (M.K. and K.S.), the Center of Excellence in Astrophysics and Associated Technologies (PFB 06), by the FONDECYT regular grant 1120061 and by the CONICYT Anillo project ACT1101 (E.T.), NASA Headquarters under the NASA Earth and Space Science Fellowship Program, grant NNX14AQ07H (M.B.), NSF award AST 1008067 (D.B.), Caltech NuSTAR subcontract 44A-1092750 and NASA ADP grant NNX10AC99G (W.N.B.), and the ASI/INAF grant I/037/12/0 011/13 and the Caltech Kingsley visitor program (A.C.). M.K. also acknowledges that support for this work was provided by the National Aeronautics and Space Administration through Chandra Award Number AR3-14010X issued by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the National Aeronautics Space Administration under contract NAS8-03060. 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. 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 research made use of the XRT Data Analysis Software (XRTDAS), archival data, software, and online services provided by the ASDC. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester. The scientific results reported in this article are based on data obtained from the Chandra Data Archive (Obs ID = 4078, 4868, 12290, 13895). This work is based on observations obtained with XMM-Newton (Obs ID = 0110930201, 0147760101, 0200430201), an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. Facilities: NuSTAR - The NuSTAR (Nuclear Spectroscopic Telescope Array) mission, Swift - , XMM - , Sloan - , CXO -
Group:Space Radiation Laboratory, NuSTAR
Funding AgencyGrant Number
Swiss National Science Foundation (SNSF)PZ00P2_154799/1
Swiss National Science Foundation (SNSF)PP00P2 138979/1
Center of Excellence in Astrophysics and Associated TechnologiesPFB 06
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1120061
Comisión Nacional de Investigación Científica y Tecnológica (CONICYT)ACT1101
NASA Earth and Space Science FellowshipNNX14AQ07H
NSFAST 1008067
Caltech NuSTAR subcontract44A-1092750
Agenzia Spaziale Italiana (ASI)I/037/12/0 011/13
Caltech Kingsley Visitor ProgramUNSPECIFIED
Subject Keywords:galaxies: active – galaxies: Seyfert – X-rays: galaxies
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory2016-45
Record Number:CaltechAUTHORS:20160729-140218146
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:69324
Deposited By: Tony Diaz
Deposited On:29 Jul 2016 21:33
Last Modified:21 Mar 2019 18:53

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