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NuSTAR and Keck Observations of Heavily Obscured Quasars Selected by WISE

Yan, Wei and Hickox, Ryan C. and Hainline, Kevin N. and Stern, Daniel and Lansbury, George and Alexander, David M. and Hviding, Raphael E. and Assef, Roberto J. and Ballantyne, David R. and DiPompeo, Michael A. and Lanz, Lauranne and Carroll, Christopher M. and Koss, Michael and Lamperti, Isabella and Civano, Francesca and Del Moro, Agnese and Gandhi, Poshak and Myers, Adam D. (2019) NuSTAR and Keck Observations of Heavily Obscured Quasars Selected by WISE. Astrophysical Journal, 870 (1). Art. No. 33. ISSN 1538-4357. doi:10.3847/1538-4357/aaeed4.

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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 ~10^(43) erg s^(−1). We compare X-ray and IR luminosities to obtain estimates of the hydrogen column densities (N_H) based on the suppression of the hard X-ray emission. We estimate N_H of these quasars to be at or larger than 10^(25) 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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Yan, Wei0000-0001-9519-1812
Hickox, Ryan C.0000-0003-1468-9526
Hainline, Kevin N.0000-0003-4565-8239
Stern, Daniel0000-0003-2686-9241
Lansbury, George0000-0002-5328-9827
Alexander, David M.0000-0002-5896-6313
Hviding, Raphael E.0000-0002-4684-9005
Assef, Roberto J.0000-0002-9508-3667
Ballantyne, David R.0000-0001-8128-6976
DiPompeo, Michael A.0000-0001-6788-1701
Lanz, Lauranne0000-0002-3249-8224
Carroll, Christopher M.0000-0003-3574-2963
Koss, Michael0000-0002-7998-9581
Lamperti, Isabella0000-0003-3336-5498
Civano, Francesca0000-0002-2115-1137
Gandhi, Poshak0000-0003-3105-2615
Additional Information:© 2019 The American Astronomical Society. Received 2018 March 7; revised 2018 October 30; accepted 2018 November 2; published 2019 January 2. 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). The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Some of the observations reported in this paper were obtained with the Southern African Large Telescope (SALT). R.C.H. acknowledges support from NASA grant NNX15AP24G and National Science Foundation CAREER Award number 1554584. R.J.A. was supported by FONDECYT grant number 1151408.
Subject Keywords:galaxies: active – galaxies: nuclei – X-rays: galaxies
Issue or Number:1
Record Number:CaltechAUTHORS:20181108-091200724
Persistent URL:
Official Citation:Wei Yan et al 2019 ApJ 870 33
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:90744
Deposited By: Joy Painter
Deposited On:08 Nov 2018 20:40
Last Modified:16 Nov 2021 03:35

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