Deficit of Hot Dust in Low-redshift Active Galactic Nuclei

TL;DR

This study investigates the hot dust deficiency in low-redshift active galactic nuclei, revealing its correlation with AGN luminosity and potential links to dust sublimation and outflows.

Contribution

It introduces a classification of AGNs based on hot dust content using broad-band SED fitting and explores the physical factors influencing hot dust deficiency.

Findings

HDD AGNs have higher average luminosity than normal and WDD AGNs.

HDD fraction is primarily connected with AGN luminosity.

Outflows may influence the hot dust component.

Abstract

We assemble a broad-band spectral energy distribution (SED) ranging from optical to mid-infrared of nearby active galactic nuclei at $z < 0.4$. SED fitting analysis is performed using semi-empirical templates derived from Palomar-Green quasars to classify the sample into normal, warm-dust-deficient (WDD), and hot-dust-deficient (HDD) AGNs. Kolmogorov-Smirnov tests reveal that HDD AGNs exhibit, on average higher AGN luminosity than normal and WDD AGNs. HDD fraction, on the other hand, is only weakly correlated with black hole mass and inversely correlated with Eddington ratio. By fixing the other parameters, we conclude that the HDD fraction is primarily connected with the AGN luminosity. It implies that there is a causal connection between the covering factor of the hot dust component and AGN luminosity, possibly due to the sublimation of the innermost dust or the thickening of the intervening gas in the broad-line region. Analysis of the outflow properties traced by the wing of [O III]$\lambda5007$ suggests that outflows may be related to the formation and maintenance of the hot dust component. Finally, we demonstrate through comparison with previous studies that the classification of HDD AGNs requires careful subtraction of the host galaxy light.