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Title: NuSTAR and XMM-Newton observations of luminous, heavily obscured, WISE-selected quasars at z ∼ 2

We report on a NuSTAR and XMM-Newton program that has observed a sample of three extremely luminous, heavily obscured WISE-selected active galactic nuclei (AGNs) at z ∼ 2 across a broad X-ray band (0.1 – 79 keV). The parent sample, selected to be faint or undetected in the WISE 3.4 μm (W1) and 4.6 μm (W2) bands but bright at 12 μm (W3) and 22 μm (W4), are extremely rare, with only ∼1000 so-called 'W1W2-dropouts' across the extragalactic sky. Optical spectroscopy reveals typical redshifts of z ∼ 2 for this population, implying rest-frame mid-IR luminosities of νL {sub ν}(6 μm) ∼ 6 × 10{sup 46} erg s{sup –1} and bolometric luminosities that can exceed L {sub bol} ∼ 10{sup 14} L {sub ☉}. The corresponding intrinsic, unobscured hard X-ray luminosities are L(2-10 keV) ∼ 4 × 10{sup 45} erg s{sup –1} for typical quasar templates. These are among the most AGNs known, though the optical spectra rarely show evidence of a broad-line region and the selection criteria imply heavy obscuration even at rest-frame 1.5 μm. We designed our X-ray observations to obtain robust detections for gas column densities N {sub H} ≤ 10{sup 24} cm{sup –2}. In fact, the sourcesmore » prove to be fainter than these predictions. Two of the sources were observed by both NuSTAR and XMM-Newton, with neither being detected by NuSTAR (f {sub 3-24} {sub keV} ≲ 10{sup –13} erg cm{sup –2} s{sup –1}), and one being faintly detected by XMM-Newton (f {sub 0.5-10} {sub keV} ∼ 5 × 10{sup –15} erg cm{sup –2} s{sup –1}). A third source was observed only with XMM-Newton, yielding a faint detection (f {sub 0.5-10} {sub keV} ∼ 7 × 10{sup –15} erg cm{sup –2} s{sup –1}). The X-ray data imply these sources are either X-ray weak, or are heavily obscured by column densities N {sub H} ≳ 10{sup 24} cm{sup –2}. The combined X-ray and mid-IR analysis seems to favor this second possibility, implying the sources are extremely obscured, consistent with Compton-thick, luminous quasars. The discovery of a significant population of heavily obscured, extremely luminous AGNs would not conform to the standard paradigm of a receding torus, in which more luminous quasars are less likely to be obscured, and instead suggests that an additional source of obscuration is present in these extreme sources.« less
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  1. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Mail Stop 169-221, Pasadena, CA 91109 (United States)
  2. Department of Physics, University of Durham, South Road, Durham DH1 3LE (United Kingdom)
  3. Núcleo de Astronomía de la Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército Libertador 441, Santiago (Chile)
  4. Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Lab, University Park, PA 16802 (United States)
  5. Center for Relativistic Astrophysics, School of Physics, Georgia Institute of Technology, Atlanta, GA 30332 (United States)
  6. Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States)
  7. Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, 306, Santiago 22 (Chile)
  8. NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
  9. Physics and Astronomy, University of Leicester, 1 University Road, Leicester, LE1 7RH (United Kingdom)
  10. Space Sciences Laboratory, University of California, Berkeley, 7 Gauss Way, Berkeley, CA 94720-7450 (United States)
  11. Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse 1, D-85748, Garching bei München (Germany)
  12. Danish Technical University, DK-2800 Lyngby (Denmark)
  13. INAF Osservatorio Astronomico di Bologna, via Ranzani 1, I-40127, Bologna (Italy)
Publication Date:
OSTI Identifier:
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 794; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States