The Differences in the Torus Geometry between Hidden and Non-hidden Broad Line Active Galactic Nuclei

Abstract

We present results from the fitting of infrared (IR) spectral energy distributions of 21 active galactic nuclei (AGNs) with clumpy torus models. We compiled high spatial resolution (~0.3–0.7 arcsec) mid-IR (MIR) N-band spectroscopy, Q-band imaging, and nuclear near- and MIR photometry from the literature. Combining these nuclear near- and MIR observations, far-IR photometry, and clumpy torus models enables us to put constraints on the torus properties and geometry. We divide the sample into three types according to the broad line region (BLR) properties: type-1s, type-2s with scattered or hidden broad line region (HBLR) previously observed, and type-2s without any published HBLR signature (NHBLR). Comparing the torus model parameters gives us the first quantitative torus geometrical view for each subgroup. We find that NHBLR AGNs have smaller torus opening angles and larger covering factors than HBLR AGNs. This suggests that the chance to observe scattered (polarized) flux from the BLR in NHBLR could be reduced by the dual effects of (a) less scattering medium due to the reduced scattering volume given the small torus opening angle and (b) the increased torus obscuration between the observer and the scattering region. These effects give a reasonable explanation for the lack of observed HBLR in some type-2 AGNs.

Additional Information

© 2015 The American Astronomical Society. Received 9 October 2014, accepted for publication 26 January 2015; Published 15 April 2015. We are grateful for useful comments from the anonymous referee. We also thank C. Ricci, T. Kawamuro, K. Matsuoka, and M. Stalevski for useful comments and discussions. K.I. thanks the Department of Physics and Astronomy at University of Texas at San Antonio, where most of the research was conducted. This paper is based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership. This work was partly supported by the Grant-in-Aid for JSPS Fellows for young researchers (K.I.). C.P. acknowledges support from UTSA and NSF (grant number 0904421). C.R.A. is supported by a Marie Curie Intra European Fellowship within the 7th European Community Framework Programme (PIEF-GA-2012-327934). A.A.-H. acknowledges support from the Spanish Plan Nacional de Astronomia y Astrofisica under grant AYA2012-31447.

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Published - 0004-637X_803_2_57.pdf

Submitted - 1501.06584v1.pdf

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