An Intermediate-mass Black Hole Hidden behind Thick Obscuration
- Creators
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Boorman, Peter G.1
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Stern, Daniel2
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Assef, Roberto J.3
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Borkar, Abhijeet4
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Brightman, Murray1
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Buchner, Johannes5, 6
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Chen, Chien-Ting7, 8
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Earnshaw, Hannah P.1
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Harrison, Fiona A.1
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Matzeu, Gabriele A.9
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Pfeifle, Ryan W.10, 11
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Ricci, Claudio3, 12
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Svoboda, Jiří4
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Torres-Albà, Núria13, 14
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Zaw, Ingyin15
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1.
California Institute of Technology
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2.
Jet Propulsion Lab
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3.
Diego Portales University
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4.
Czech Academy of Sciences
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5.
Max Planck Institute for Extraterrestrial Physics
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6.
Excellence Cluster Universe
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7.
Universities Space Research Association
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8.
Marshall Space Flight Center
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9.
European Space Astronomy Centre
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10.
Goddard Space Flight Center
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11.
Oak Ridge Associated Universities
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12.
Peking University
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13.
Clemson University
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14.
University of Virginia
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15.
New York University Abu Dhabi
Abstract
Recent models suggest approximately half of all accreting supermassive black holes (SMBHs; MBH ≳ 105M⊙) are expected to undergo intense growth phases behind Compton-thick (NH > 1.5 × 1024 cm−2) veils of obscuring gas. However, despite being a viable source for the seeding of SMBHs, there are currently no examples known of a Compton-thick accreting intermediate-mass black hole (IMBH; MBH ∼ 102–105M⊙). We present a detailed X-ray spectral analysis of IC 750—the only active galactic nuclei (AGN) to date with a precise megamaser-based intermediate mass <105M⊙. We find the equivalent width of neutral 6.4 keV Fe Kα to be 1.9_(−1.0)^(+2.2) keV via phenomenological modeling of the coadded 177 ks Chandra spectrum. Such large equivalent widths are seldom produced by processes other than fluorescence from dense obscuration. We fit three physically motivated X-ray spectral models to infer a range of possible intrinsic 2–10 keV luminosity posteriors that encompass the systematic uncertainties associated with a choice of model. Despite a wide range of predicted intrinsic 2–10 keV luminosities between ∼ 1041 and 1043 erg s−1, all three models agree that IC 750 has a Compton-thick line-of-sight column density to >99% confidence. Compton-thick obscuration is well-documented to impinge substantial bias on the pursuit of SMBH AGN. Our results thus provide the first indication that Compton-thick obscuration should also be properly considered to uncover and understand the IMBH population in an unbiased manner.
Copyright and License
© 2024. The Author(s). Published by the American Astronomical Society.
Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Acknowledgement
We thank the anonymous referee for their constructive comments that helped to improve the manuscript. P.G.B. would also like to thank Megan Urry, Colin Burke, and Francesca Civano for their useful discussions.
The work of D.S. was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA.
R.J.A. was supported by FONDECYT grant number 1231718 and by the ANID BASAL project FB210003.
R.W.P. gratefully acknowledges support through an appointment to the NASA Postdoctoral Program at Goddard Space Flight Center, administered by ORAU through a contract with NASA.
C.R. acknowledges support from Fondecyt Regular grant 1230345, ANID BASAL project FB210003, and the China–Chile joint research fund.
N.T.A. acknowledges funding from NASA under contracts 80NSSC23K0484 and 80NSSC23K1611.
This research has made use of data obtained from the Chandra Data Archive and the Chandra Source Catalog, and software provided by the Chandra X-ray Center (CXC) in the application packages CIAO and Sherpa.
This research is based on observations made with the NASA/ESA Hubble Space Telescope obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program(s).
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.
This research has made use of NASA's Astrophysics Data System Bibliographic Services.
This paper employs a list of Chandra data sets obtained by the Chandra X-ray Observatory, contained in doi:10.25574/cdc.287.
Facilities
CXO - Chandra X-ray Observatory satellite, HST - Hubble Space Telescope satellite.
Software References
This paper made extensive use of matplotlib (J. D. Hunter 2007), pandas (W. McKinney 2010; pandas development team 2020), and astropy (Astropy Collaboration et al. 2013, 2018, 2022).
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Additional details
- Jet Propulsion Laboratory
- Fondo Nacional de Desarrollo Científico y Tecnológico
- 1231718
- Agencia Nacional de Investigación y Desarrollo
- FB210003
- National Aeronautics and Space Administration
- NASA Postdoctoral Program
- Fondo Nacional de Desarrollo Científico y Tecnológico
- 1230345
- Agencia Nacional de Investigación y Desarrollo
- FB210003
- Chinese Academy of Science South America Center for Astronomy
- National Aeronautics and Space Administration
- 80NSSC23K0484
- National Aeronautics and Space Administration
- 80NSSC23K1611
- National Aeronautics and Space Administration
- NAS 5-26555
- Accepted
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2024-09-23
- Available
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2024-11-06Published
- Caltech groups
- Astronomy Department, Division of Physics, Mathematics and Astronomy (PMA)
- Publication Status
- Published