Connection between mid-infrared emission properties and narrow-line region outflows in type 1 active galactic nuclei

Abstract

The location of warm dust producing the mid-infrared (MIR) emission in type 1 active galactic nuclei (AGNs) is complex and not yet fully known. We explore this problem by studying how the MIR covering factor (CFMIR = L MIR/L bol) correlates with the fundamental parameters of AGN accretion process (such as L bol, black hole mass M BH, and Eddington ratio L/L Edd) and the properties of narrow emission lines (as represented by [O III] λ5007), using large data sets derived from the Sloan Digital Sky Spectroscopic Survey (SDSS) and the Wide Infrared Sky Survey (WISE). First, we find that the luminosity of the [O III] wing component (L wing) correlates more tightly with the continuum luminosity (λLȮλ(5100)) than the luminosity of the line core component (L core) does, which is in line with our previous conclusion that the wing component, generally blueshifted, originates from the polar outflows in the inner narrow-line region (NLR). We then find that the MIR CF shows the strongest correlation with L wing/L bol rather than with L core/L bol or the above fundamental AGN parameters, and the correlation becomes stronger as the infrared wavelength increases. We also confirm the anti-correlations of CFMIR with L bol and M BH, and the lack of dependence of CFMIR on the Eddington ratio. These results suggest that a large fraction of the warm dust producing MIR emission in AGNs is likely embedded in polar outflows in the NLR instead of in the torus. © 2013. The American Astronomical Society. All rights reserved.