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 (CF_(MIR) = 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 (λL_λ(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 CF_(MIR) with L_(bol) and M_(BH), and the lack of dependence of CF_(MIR) 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.