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Unobscured Type 2 Active Galactic Nuclei

Shi, Yong and Rieke, George H. and Smith, Paul and Rigby, Jane and Hines, Dean and Donley, Jennifer and Schmidt, Gary and Diamond-Stanic, Aleksandar M. (2010) Unobscured Type 2 Active Galactic Nuclei. Astrophysical Journal, 714 (1). pp. 115-129. ISSN 0004-637X.

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Type 2 active galactic nuclei (AGNs) with intrinsically weak broad emission lines (BELs) would be exceptions to the unified model. After examining a number of proposed candidates critically, we find that the sample is contaminated significantly by objects with BELs of strengths indicating that they actually contain intermediate-type AGNs, plus a few Compton-thick sources as revealed by extremely low ratios of X-ray to nuclear IR luminosities. We develop quantitative metrics that show two (NGC 3147 and NGC 4594) of the remaining candidates to have BELs 2-3 orders of magnitude weaker than those of typical type 1 AGNs. Several more galaxies remain as candidates to have anomalously weak BELs, but this status cannot be confirmed with the existing information. Although the parent sample is poorly defined, the two confirmed objects are well under 1% of its total number of members, showing that the absence of a BEL is possible, but very uncommon in AGN. We evaluate these two objects in detail using multi-wavelength measurements including new IR data obtained with Spitzer and ground-based optical spectropolarimeteric observations. They have little X-ray extinction with N_H < ~10^(21) cm^(–2). Their IR spectra show strong silicate emission (NGC 4594) or weak aromatic features on a generally power-law continuum with a suggestion of silicates in emission (NGC 3147). No polarized BEL is detected in NGC 3147. These results indicate that the two unobscured type 2 objects have circumnuclear tori that are approximately face-on. Combined with their X-ray and optical/UV properties, this behavior implies that we have an unobscured view of the nuclei and thus that they have intrinsically weak BELs. We compare their properties with those of the other less-extreme candidates. We then compare the distributions of bolometric luminosities and accretion rates of these objects with theoretical models that predict weak BELs.

Item Type:Article
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URLURL TypeDescription
Shi, Yong0000-0002-8614-6275
Rieke, George H.0000-0003-2303-6519
Rigby, Jane0000-0002-7627-6551
Hines, Dean0000-0003-4653-6161
Additional Information:© 2010 American Astronomical Society. Received 2009 August 26; accepted 2010 March 15; published 2010 April 7. We thank the anonymous referee for detailed comments. Support for this work was provided by NASA through contract 1255094 issued by JPL/California Institute of Technology. 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 the NASA/IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.
Funding AgencyGrant Number
Subject Keywords:galaxies: nuclei; galaxies: Seyfert
Issue or Number:1
Classification Code:PACS: 98.54.Cm; 98.62.Qz; 98.70.Qy; 98.58.Bz; 98.58.Ge; 98.62.Mw
Record Number:CaltechAUTHORS:20100609-135844437
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Official Citation:Yong Shi et al 2010 ApJ 714 115 doi: 10.1088/0004-637X/714/1/115
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:18623
Deposited By: Jason Perez
Deposited On:10 Jun 2010 18:38
Last Modified:09 Mar 2020 13:19

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