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A hard X-ray view of luminous and ultra-luminous infrared galaxies in GOALS – I. AGN obscuration along the merger sequence

Ricci, C. and Privon, G. C. and Pfeifle, R. W. and Armus, L. and Iwasawa, K. and Torres-Albà, N. and Satyapal, S. and Bauer, F. E. and Treister, E. and Ho, L. C. and Aalto, S. and Arévalo, P. and Barcos-Muñoz, L. and Charmandaris, V. and Díaz-Santos, T. and Evans, A. S. and Gao, T. and Inami, H. and Koss, M. J. and Lansbury, G. and Linden, S. T. and Medling, A. and Sanders, D. B. and Song, Y. and Stern, D. and U, V. and Ueda, Y. and Yamada, S. (2021) A hard X-ray view of luminous and ultra-luminous infrared galaxies in GOALS – I. AGN obscuration along the merger sequence. Monthly Notices of the Royal Astronomical Society, 506 (4). pp. 5935-5950. ISSN 0035-8711. doi:10.1093/mnras/stab2052.

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The merger of two or more galaxies can enhance the inflow of material from galactic scales into the close environments of active galactic nuclei (AGNs), obscuring and feeding the supermassive black hole (SMBH). Both recent simulations and observations of AGN in mergers have confirmed that mergers are related to strong nuclear obscuration. However, it is still unclear how AGN obscuration evolves in the last phases of the merger process. We study a sample of 60 luminous and ultra-luminous IR galaxies (U/LIRGs) from the GOALS sample observed by NuSTAR. We find that the fraction of AGNs that are Compton thick (CT; N_H ≥ 10²⁴cm⁻²⁠) peaks at 74⁺¹⁴₋₁₉ per cent at a late merger stage, prior to coalescence, when the nuclei have projected separations (d_(sep)) of 0.4–6 kpc. A similar peak is also observed in the median N_H[(1.6 ± 0.5) × 10²⁴ cm⁻²]. The vast majority (⁠85⁺⁷₋₉ per cent) of the AGNs in the final merger stages (d_(sep) ≲ 10 kpc) are heavily obscured (⁠N_H ≥ 10²³ cm⁻²⁠), and the median N_H of the accreting SMBHs in our sample is systematically higher than that of local hard X-ray-selected AGN, regardless of the merger stage. This implies that these objects have very obscured nuclear environments, with the N_H ≥ 10²³ cm⁻² gas almost completely covering the AGN in late mergers. CT AGNs tend to have systematically higher absorption-corrected X-ray luminosities than less obscured sources. This could either be due to an evolutionary effect, with more obscured sources accreting more rapidly because they have more gas available in their surroundings, or to a selection bias. The latter scenario would imply that we are still missing a large fraction of heavily obscured, lower luminosity (⁠L₂₋₁₀ ≲ 10⁴³ ergs⁻¹⁠) AGNs in U/LIRGs.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Ricci, C.0000-0001-5231-2645
Privon, G. C.0000-0003-3474-1125
Pfeifle, R. W.0000-0001-8640-8522
Armus, L.0000-0003-3498-2973
Iwasawa, K.0000-0002-4923-3281
Torres-Albà, N.0000-0003-3638-8943
Bauer, F. E.0000-0002-8686-8737
Treister, E.0000-0001-7568-6412
Arévalo, P.0000-0001-8503-9809
Barcos-Muñoz, L.0000-0003-0057-8892
Charmandaris, V.0000-0002-2688-1956
Díaz-Santos, T.0000-0003-0699-6083
Evans, A. S.0000-0003-2638-1334
Inami, H.0000-0003-4268-0393
Koss, M. J.0000-0002-7998-9581
Lansbury, G.0000-0002-5328-9827
Linden, S. T.0000-0002-1000-6081
Medling, A.0000-0001-7421-2944
Sanders, D. B.0000-0002-1233-9998
Stern, D.0000-0003-2686-9241
U, V.0000-0002-1912-0024
Ueda, Y.0000-0001-7821-6715
Yamada, S.0000-0002-2166-5605
Additional Information:© 2021 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2021 July 9. Received 2021 July 2; in original form 2021 May 20. Published: 19 July 2021. We thank the referee for their useful suggestions, which helped us in improving the quality of the manuscript. We thank Chin-Shin Chang for useful comments on the manuscript. LCH was supported by the National Key Research and Development Program of China (2016YFA0400702) and the National Science Foundation of China (11721303 and 11991052). CR acknowledges support from the Fondecyt Iniciacion grant 11190831. ET acknowledges support from CATA-Basal AFB-170002, FONDECYT Regular grant 1190818, ANID Anillo ACT172033, and Millennium Nucleus NCN19_058 (TITANs). FEB acknowledges support from ANID – Millennium Science Initiative Program – ICN12_009, CATA-Basal – AFB-170002, and FONDECYT Regular – 1190818 and 1200495. SA gratefully acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 789410). VU acknowledges funding support from NASA Astrophysics Data Analysis Program (ADAP) Grant 80NSSC20K0450. AMM acknowledges support from the National Science Foundation under grant number 2009416. KI acknowledges support by the Spanish MICINN under grant Proyecto/AEI/10.13039/501100011033 and ‘Unit of excellence María de Maeztu 2020-2023’ awarded to ICCUB (CEX2019-000918-M). PA acknowledges financial support from ANID Millennium Nucleus NCN19-058 (TITANS) and the Max Planck Society through a Partner Group. HI acknowledges support from JSPS KAKENHI Grant Number JP19K23462. 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. Data Availability: The data sets generated and/or analysed in this study are available from the corresponding author on reasonable request.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
National Key Research and Development Program of China2016YFA0400702
National Natural Science Foundation of China11721303
National Natural Science Foundation of China11991052
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)11190831
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1190818
Comisión Nacional de Investigación Científica y Tecnológica (CONICYT)ACT172033
Agencia Nacional de Investigación y Desarrollo (ANID)NCN19_058
Comisión Nacional de Investigación Científica y Tecnológica (CONICYT)ICN12_009
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1200495
European Research Council (ERC)789410
Ministerio de Ciencia e Innovación (MCINN)Proyecto/AEI/10.13039/501100011033
Centro de Excelencia Severo OchoaCEX2019-000918-M
Max Planck SocietyUNSPECIFIED
Japan Society for the Promotion of Science (JSPS)JP19K23462
Subject Keywords:galaxies: active – quasars: general – galaxies: Seyfert – infrared: galaxies –X-rays: general
Issue or Number:4
Record Number:CaltechAUTHORS:20211112-175932285
Persistent URL:
Official Citation:C Ricci, G C Privon, R W Pfeifle, L Armus, K Iwasawa, N Torres-Albà, S Satyapal, F E Bauer, E Treister, L C Ho, S Aalto, P Arévalo, L Barcos-Muñoz, V Charmandaris, T Diaz-Santos, A S Evans, T Gao, H Inami, M J Koss, G Lansbury, S T Linden, A Medling, D B Sanders, Y Song, D Stern, V U, Y Ueda, S Yamada, A hard X-ray view of luminous and ultra-luminous infrared galaxies in GOALS – I. AGN obscuration along the merger sequence, Monthly Notices of the Royal Astronomical Society, Volume 506, Issue 4, October 2021, Pages 5935–5950,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:111855
Deposited By: Tony Diaz
Deposited On:12 Nov 2021 21:27
Last Modified:12 Nov 2021 21:27

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