Journal
ASTROPHYSICAL JOURNAL
Volume 794, Issue 2, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/794/2/102
Keywords
galaxies: active; quasars: individual (WISEA J181417.29+341224.8, WISEA J220743.82+193940.1, WISEA J235710.82+032802
Categories
Funding
- NASA [NNG08FD60C]
- National Aeronautics and Space Administration
- Science and Technology Facilities Council (STFC) [ST/K501979/1, ST/I001573/1, ST/J003697/1]
- Leverhulme Trust
- Gemini-CONICYT [32120009]
- CONICYT-Chile [Basal-CATA PFB-06/2007, FONDECYT 1141218, EMBIGGEN Anillo ACT1101]
- Project IC120009 Millennium Institute of Astrophysics (MAS) of Iniciativa Cientifica Milenio del Ministerio de Economia, Fomento y Turismo
- ASI-INAF [I/37/012/0-011/13]
- NASA through ADAP [NNX12AE38G]
- National Science Foundation [1211096]
- Swiss National Science Foundation (NSF) [PP00P2 138979/1]
- Science and Technology Facilities Council [ST/L00075X/1, ST/I001573/1, ST/K501979/1, ST/J003697/2, ST/J003697/1] Funding Source: researchfish
- Division Of Astronomical Sciences
- Direct For Mathematical & Physical Scien [1211096] Funding Source: National Science Foundation
- STFC [ST/I001573/1, ST/K501979/1, ST/J003697/1, ST/J003697/2, ST/L00075X/1] Funding Source: UKRI
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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 similar to 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 mu m (W1) and 4.6 mu m (W2) bands but bright at 12 mu m (W3) and 22 mu m (W4), are extremely rare, with only similar to 1000 so-called W1W2-dropouts across the extragalactic sky. Optical spectroscopy reveals typical redshifts of z similar to 2 for this population, implying rest-frame mid-IR luminosities of nu L-nu (6 mu m) similar to 6 x 10(46) erg s(-1) and bolometric luminosities that can exceed L-bol similar to 10(14) L-circle dot. The corresponding intrinsic, unobscured hard X-ray luminosities are L(2-10 keV) similar to 4 x 10(45) erg s-(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 1.5mm. We designed our X-ray observations to obtain robust detections for gas column densities N-H <= 10(24) cm(-2). In fact, the sources 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(3-24 keV) less than or similar to 10(-13) erg cm(-2) s(-1)), and one being faintly detected by XMM-Newton (f(0.5-10 keV) similar to 5 x 10(-15) erg cm(-2) s(-1)). A third source was observed only with XMM-Newton, yielding a faint detection (f(0.5-10 keV) similar to 7 x 10(-15) erg cm(-2) s(-1)). The X-ray data imply these sources are either X-ray weak, or are heavily obscured by column densities N-H greater than or similar to 10(24) cm(-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.
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