2013ApJ...768...22Z

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_boland 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.