Connection Between Mid-Infrared Emission Properties and Narrow Line Region Outflows in Type 1 Active Galactic Nuclei

TL;DR

This study investigates how mid-infrared emission in Type 1 AGNs relates to narrow line region outflows, revealing that MIR emission is likely associated with polar outflows rather than the traditional torus structure.

Contribution

It demonstrates a strong correlation between MIR covering factor and outflow-related emission line properties, suggesting a new understanding of dust location in AGNs.

Findings

MIR covering factor correlates with outflow indicators more than fundamental parameters.

Warm dust MIR emission is likely embedded in polar outflows, not the torus.

Correlation strength increases with infrared wavelength.

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 MBH, and Eddington ratio L/LEdd) and the properties of narrow emission lines (as represented by [O III] 5007), using large data sets derived from the Sloan Digital Sky Spectroscopic Survey (SDSS) and the Wide Infrared Sky Survey (WISE). Firstly we find that the luminosity of the [O III] wing component (Lwing) correlates more tightly with the continuum luminosity (L5100) than the luminosity of the line core component (Lcore) 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 Lwing/L_{bol} rather than with Lcore/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 MBH, 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.