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NuSTAR and Keck observations of heavily obscured quasars selected by WISE

NuSTAR and Keck observations of heavily obscured quasars selected by WISE
NuSTAR and Keck observations of heavily obscured quasars selected by WISE

A primary aim of the Nuclear Spectroscopic Telescope Array (NuSTAR) mission is to find and characterize heavily obscured Active Galactic Nuclei (AGNs). Based on mid-infrared photometry from the Wide-Field Infrared Survey Explorer (WISE) and optical photometry from the Sloan Digital Sky Surveys, we have selected a large population of luminous obscured AGNs (i.e., "obscured quasars"). Here we report NuSTAR observations of four WISE-selected heavily obscured quasars for which we have optical spectroscopy from the Southern African Large Telescope and W. M. Keck Observatory. Optical diagnostics confirm that all four targets are AGNs. With NuSTAR hard X-ray observations, three of the four objects are undetected, while the fourth has a marginal detection. We confirm that these objects have observed hard X-ray (10-40 keV) luminosities at or below ∼1043 erg s-1. We compare X-ray and IR luminosities to obtain estimates of the hydrogen column densities (NH) based on the suppression of the hard X-ray emission.We estimate NH of these quasars to be at or larger than 1025 cm-2, confirming that WISE and optical selection can identify very heavily obscured quasars that may be missed in X-ray surveys, and they do not contribute significantly to the cosmic X-ray background. From the optical Balmer decrements, we found that our three extreme obscured targets lie in highly reddened host environments. This galactic extinction cannot adequately explain the more obscured AGNs, but it may imply a different scale of obscuration in the galaxy.

galaxies: active, galaxies: nuclei, X-rays: galaxies
0004-637X
Yan, Wei
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Hickox, Ryan C.
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Hainline, Kevin N.
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Stern, Daniel
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Lansbury, George
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Alexander, David M.
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Hviding, Raphael E.
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Assef, Roberto J.
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Ballantyne, David R.
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Dipompeo, Michael A.
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Lanz, Lauranne
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Carroll, Christopher M.
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Koss, Michael
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Lamperti, Isabella
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Civano, Francesca
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Moro, Agnese Del
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Gandhi, Poshak
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Myers, Adam D.
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Yan, Wei
f5fa4872-fd83-4511-8478-8616d520c77d
Hickox, Ryan C.
fa3d8d11-419b-4625-892f-7183fba98e8a
Hainline, Kevin N.
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Stern, Daniel
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Lansbury, George
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Alexander, David M.
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Hviding, Raphael E.
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Assef, Roberto J.
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Ballantyne, David R.
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Dipompeo, Michael A.
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Lanz, Lauranne
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Carroll, Christopher M.
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Koss, Michael
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Lamperti, Isabella
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Civano, Francesca
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Moro, Agnese Del
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Gandhi, Poshak
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Myers, Adam D.
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Yan, Wei, Hickox, Ryan C., Hainline, Kevin N., Stern, Daniel, Lansbury, George, Alexander, David M., Hviding, Raphael E., Assef, Roberto J., Ballantyne, David R., Dipompeo, Michael A., Lanz, Lauranne, Carroll, Christopher M., Koss, Michael, Lamperti, Isabella, Civano, Francesca, Moro, Agnese Del, Gandhi, Poshak and Myers, Adam D. (2019) NuSTAR and Keck observations of heavily obscured quasars selected by WISE. Astrophysical Journal, 870 (1), [33]. (doi:10.3847/1538-4357/aaeed4).

Record type: Article

Abstract

A primary aim of the Nuclear Spectroscopic Telescope Array (NuSTAR) mission is to find and characterize heavily obscured Active Galactic Nuclei (AGNs). Based on mid-infrared photometry from the Wide-Field Infrared Survey Explorer (WISE) and optical photometry from the Sloan Digital Sky Surveys, we have selected a large population of luminous obscured AGNs (i.e., "obscured quasars"). Here we report NuSTAR observations of four WISE-selected heavily obscured quasars for which we have optical spectroscopy from the Southern African Large Telescope and W. M. Keck Observatory. Optical diagnostics confirm that all four targets are AGNs. With NuSTAR hard X-ray observations, three of the four objects are undetected, while the fourth has a marginal detection. We confirm that these objects have observed hard X-ray (10-40 keV) luminosities at or below ∼1043 erg s-1. We compare X-ray and IR luminosities to obtain estimates of the hydrogen column densities (NH) based on the suppression of the hard X-ray emission.We estimate NH of these quasars to be at or larger than 1025 cm-2, confirming that WISE and optical selection can identify very heavily obscured quasars that may be missed in X-ray surveys, and they do not contribute significantly to the cosmic X-ray background. From the optical Balmer decrements, we found that our three extreme obscured targets lie in highly reddened host environments. This galactic extinction cannot adequately explain the more obscured AGNs, but it may imply a different scale of obscuration in the galaxy.

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NuSTAR and Keck Observations of Heavily Obscured Quasars Selected by WISE - Accepted Manuscript
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Accepted/In Press date: 2 November 2018
e-pub ahead of print date: 2 January 2019
Published date: January 2019
Keywords: galaxies: active, galaxies: nuclei, X-rays: galaxies

Identifiers

Local EPrints ID: 427945
URI: http://eprints.soton.ac.uk/id/eprint/427945
ISSN: 0004-637X
PURE UUID: 4985e02e-2cd8-49a4-bf6a-ff27a6b47665
ORCID for Poshak Gandhi: ORCID iD orcid.org/0000-0003-3105-2615

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Date deposited: 05 Feb 2019 17:30
Last modified: 09 Oct 2020 16:37

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Contributors

Author: Wei Yan
Author: Ryan C. Hickox
Author: Kevin N. Hainline
Author: Daniel Stern
Author: George Lansbury
Author: David M. Alexander
Author: Raphael E. Hviding
Author: Roberto J. Assef
Author: David R. Ballantyne
Author: Michael A. Dipompeo
Author: Lauranne Lanz
Author: Christopher M. Carroll
Author: Michael Koss
Author: Isabella Lamperti
Author: Francesca Civano
Author: Agnese Del Moro
Author: Poshak Gandhi ORCID iD
Author: Adam D. Myers

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