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Growing supermassive black holes in the late stages of galaxy mergers are heavily obscured

Ricci, C. and Bauer, F. E. and Treister, E. and Schawinski, K. and Privon, G. C. and Blecha, L. and Arévalo, P. and Armus, L. and Harrison, F. A. and Ho, L. C. and Iwasawa, K. and Sanders, D. B. and Stern, D. (2017) Growing supermassive black holes in the late stages of galaxy mergers are heavily obscured. Monthly Notices of the Royal Astronomical Society, 468 . pp. 1273-1299. ISSN 0035-8711. doi:10.1093/mnras/stx173.

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Mergers of galaxies are thought to cause significant gas inflows to the inner parsecs, which can activate rapid accretion on to supermassive black holes (SMBHs), giving rise to active galactic nuclei (AGN). During a significant fraction of this process, SMBHs are predicted to be enshrouded by gas and dust. Studying 52 galactic nuclei in infrared-selected local luminous and ultraluminous infrared galaxies in different merger stages in the hard X-ray band, where radiation is less affected by absorption, we find that the amount of material around SMBHs increases during the last phases of the merger. We find that the fraction of Compton-thick (CT, NH ≥ 10^(24) cm^−2) AGN in late-merger galaxies is higher (fCT = 65+12 −13 per cent) than in local hard X-ray selected AGN (f CT = 27 ± 4 per cent), and that obscuration reaches its maximum when the nuclei of the two merging galaxies are at a projected distance of D12 ≃ 0.4–10.8 kpc (fCT = 77+13 −17 per cent). We also find that all AGN of our sample in late-merger galaxies have NH > 10^(23) cm^−2, which implies that the obscuring material covers 95+4 −8 per cent of the X-ray source. These observations show that the material is most effectively funnelled from the galactic scale to the inner tens of parsecs during the late stages of galaxy mergers, and that the close environment of SMBHs in advanced mergers is richer in gas and dust with respect to that of SMBHs in isolated galaxies, and cannot be explained by the classical AGN unification model in which the torus is responsible for the obscuration.

Item Type:Article
Related URLs:
URLURL TypeDescription
Ricci, C.0000-0001-5231-2645
Bauer, F. E.0000-0002-8686-8737
Treister, E.0000-0001-7568-6412
Schawinski, K.0000-0001-5464-0888
Privon, G. C.0000-0003-3474-1125
Blecha, L.0000-0002-2183-1087
Armus, L.0000-0003-3498-2973
Harrison, F. A.0000-0003-2992-8024
Ho, L. C.0000-0001-6947-5846
Iwasawa, K.0000-0002-4923-3281
Sanders, D. B.0000-0002-1233-9998
Stern, D.0000-0003-2686-9241
Additional Information:© 2017 The Authors. Accepted 2017 January 18. Received 2017 January 17; in original form 2016 December 2. We thank the referee for the careful reading of the manuscript and for the prompt report that helped us improve the quality of the paper. We thank the NuSTAR Cycle 1 TAC for the NuSTAR data on which this paper is based, Chin-Shin Chang, George Lansbury, Dave Alexander and Johannes Buchner for useful comments on the manuscript. 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 (Caltech, USA), and of the NASA/ IPAC Infrared Science Archive and NASA/IPAC Extragalactic Database (NED), which are operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. We acknowledge financial support from the CONICYT-Chile grants ‘EMBIGGEN’ Anillo ACT1101 (CR, FEB, ET), FONDECYT 1141218 (CR, FEB), FONDECYT 1160999 (ET), FONDECYT 3150361 (GP), Basal- CATA PFB–06/2007 (CR, FEB, ET), the NASA NuSTAR AO1 Award NNX15AV27G (FEB), the China-CONICYT fund (CR), the Swiss National Science Foundation (Grant PP00P2_138979/1 and PP00P2_166159, KS), the Chinese Academy of Science grant
Group:Space Radiation Laboratory, NuSTAR, Infrared Processing and Analysis Center (IPAC), Astronomy Department
Funding AgencyGrant Number
Swiss National Science Foundation (SNSF)PP00P2_138979/1
Swiss National Science Foundation (SNSF)PP00P2_166159
Chinese Academy of ScienceXDB09030102
National Natural Science Foundation of China11473002
Ministry of Science and Technology (China)2016YFA0400702
Ministerio de Economía, Industria y Competitividad (MINECO)AYA2013-47447-C3-2-P
Iniciativa Científica Milenio del Ministerio de Economía, Fomento y TurismoIC120009
Record Number:CaltechAUTHORS:20170525-121504076
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:77760
Deposited By: Joy Painter
Deposited On:25 May 2017 20:36
Last Modified:15 Nov 2021 17:33

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