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NuSTAR Reveals Extreme Absorption in z < 0.5 Type 2 Quasars

Lansbury, G. B. and Gandhi, P. and Alexander, D. M. and Assef, R. J. and Aird, J. and Annuar, A. and Ballantyne, D. R. and Baloković, M. and Bauer, F. E. and Boggs, S. E. and Brandt, W. N. and Brightman, M. and Christensen, F. E. and Civano, F. and Comastri, A. and Craig, W. W. and Del Moro, A. and Grefenstette, B. W. and Hailey, C. J. and Harrison, F. A. and Hickox, R. C. and Koss, M. and LaMassa, S. M. and Luo, B. and Puccetti, S. and Stern, D. and Treister, E. and Vignali, C. and Zappacosta, L. and Zhang, W. W. (2015) NuSTAR Reveals Extreme Absorption in z < 0.5 Type 2 Quasars. Astrophysical Journal, 809 (2). Art. No. 115. ISSN 0004-637X.

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The intrinsic column density (N_H) distribution of quasars is poorly known. At the high obscuration end of the quasar population and for redshifts z < 1, the X-ray spectra can only be reliably characterized using broad-band measurements that extend to energies above 10 keV. Using the hard X-ray observatory NuSTAR, along with archival Chandra and XMM-Newton data, we study the broad-band X-ray spectra of nine optically selected (from the SDSS), candidate Compton-thick (N_H > 1.5 × 10^(24) cm^(−2)) type 2 quasars (CTQSO2s); five new NuSTAR observations are reported herein, and four have been previously published. The candidate CTQSO2s lie at z < 0.5, have observed [O III] luminosities in the range 8.4 < log(L_([O III])/L⊙) < 9.6, and show evidence for extreme, Compton-thick absorption when indirect absorption diagnostics are considered. Among the nine candidate CTQSO2s, five are detected by NuSTAR in the high-energy (8–24 keV) band: two are weakly detected at the ≈3σ confidence level and three are strongly detected with sufficient counts for spectral modeling (≳90 net source counts at 8–24 keV). For these NuSTAR-detected sources direct (i.e., X-ray spectral) constraints on the intrinsic active galactic nucleus properties are feasible, and we measure column densities ≈2.5–1600 times higher and intrinsic (unabsorbed) X-ray luminosities ≈10–70 times higher than pre-NuSTAR constraints from Chandra and XMM-Newton. Assuming the NuSTAR-detected type 2 quasars are representative of other Compton-thick candidates, we make a correction to the N_H distribution for optically selected type 2 quasars as measured by Chandra and XMM-Newton for 39 objects. With this approach, we predict a Compton-thick fraction of f_(CT) = 36^(+14)_(-12)%, although higher fractions (up to 76%) are possible if indirect absorption diagnostics are assumed to be reliable.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Lansbury, G. B.0000-0002-5328-9827
Gandhi, P.0000-0003-3105-2615
Alexander, D. M.0000-0002-5896-6313
Assef, R. J.0000-0002-9508-3667
Aird, J.0000-0003-1908-8463
Ballantyne, D. R.0000-0001-8128-6976
Bauer, F. E.0000-0002-8686-8737
Boggs, S. E.0000-0001-9567-4224
Brandt, W. N.0000-0002-0167-2453
Comastri, A.0000-0003-3451-9970
Harrison, F. A.0000-0003-2992-8024
Koss, M.0000-0002-7998-9581
Luo, B.0000-0002-9036-0063
Puccetti, S.0000-0002-2734-7835
Stern, D.0000-0003-2686-9241
Additional Information:© 2015 The American Astronomical Society. Received 2015 February 12; accepted 2015 June 12; published 2015 August 14. We thank the referee for a careful review, which has improved this work. We acknowledge financial support from: the Science and Technology Facilities Council (STFC) grants ST/K501979/1 (G.B.L.), ST/J003697/1 (P.G.), ST/I001573/1 (D.M.A. and A.D.M.); the Leverhulme Trust (D.M.A.); Gemini-CONICYT grant 32120009 (R.J.A.); the ERC Advanced Grant FEEDBACK at the University of Cambridge (J.A.); NSF AST award 1008067 (D.R.B.); the NASA Earth and Space Science Fellowship Program, grant NNX14AQ07H (M.B.); CONICYT-Chile grants Basal-CATA PFB-06/2007 (F.E.B.), FONDECYT 1141218 (F.E.B.), and "EMBIGGEN" Anillo ACT1101 (F.E.B.); the Ministry of Economy, Development, and Tourism's Millennium Science Initiative grant IC120009, awarded to The Millennium Institute of Astrophysics, MAS (F.E.B.); Caltech NuSTAR subcontract 44A-1092750 (W.N.B. and B.L.); NASA ADP grant NNX10AC99G (W.N.B. and B.L.); the Caltech Kingsley visitor program (A.C.); ASI/INAF grant I/037/12/0011/13 (A.C., S.P., C.V.); NASA ADAP award NNX12AE38G (R.C.H.); National Science Foundation grant 1211096 (R.C.H.); and Swiss National Science Foundation grant PP00P2_138979/1 (M.K.). We thank Andrew Ptak and Jianjun Jia for the useful correspondence. 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). Facilities: Chandra, IRAS, NuSTAR, Sloan, Spitzer, Swift, WISE, XMM-Newton.
Group:NuSTAR, Space Radiation Laboratory
Funding AgencyGrant Number
Science and Technology Facilities Council (STFC) ST/K501979/1
Science and Technology Facilities Council (STFC) ST/J003697/1
Science and Technology Facilities Council (STFC)ST/I001573/1
Leverhulme TrustUNSPECIFIED
Comisión Nacional de Investigación Científica y Tecnológica (CONICYT)32120009
European Research Council (ERC)FEEDBACK
NASA Earth and Space Science FellowshipNNX14AQ07H
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1141218
Comisión Nacional de Investigación Científica y Tecnológica (CONICYT)ACT1101
Iniciativa Científica Milenio del Ministerio de Economía, Fomento y TurismoIC120009
Caltech NuSTAR subcontract44A-1092750
Agenzia Spaziale Italiana (ASI)I/037/12/0011/13
Istituto Nazionale di Astrofisica (INAF)UNSPECIFIED
Swiss National Science Foundation (SNSF)PP00P2_138979/1
Caltech Kingsley Foundation FellowshipUNSPECIFIED
Subject Keywords:galaxies: active – X-rays: galaxies
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory2015-42
Record Number:CaltechAUTHORS:20150708-124636254
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:58811
Deposited By: Joy Painter
Deposited On:08 Jul 2015 22:07
Last Modified:21 Mar 2019 18:57

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