Dusty Structure Around Type-I Active Galactic Nuclei: Clumpy Torus Narrow Line Region and Near-Nucleus Hot Dust

TL;DR

This study models the infrared spectra of luminous QSOs using a three-component approach, revealing the structure and properties of the dusty torus, NLR clouds, and hot dust near the nucleus, and their relation to AGN luminosity.

Contribution

It introduces a comprehensive three-component model including a clumpy torus, NLR clouds, and hot dust, allowing for consistent spectral fitting of type-I AGNs and detailed structural analysis.

Findings

Torus covering factor correlates with bolometric luminosity.

Hot dust contributes significantly to 2-7 um radiation.

NLR clouds are located ~700 times beyond dust sublimation radius.

Abstract

We fitted Spitzer/IRS ~2-35 um spectra of 26 luminous QSOs in attempt to define the main emission components. Our model has three major components: a clumpy torus, dusty narrow line region (NLR) clouds and a blackbody-like dust. The models utilize the clumpy torus of Nenkova et al. (2008) and are the first to allow its consistent check in type-I AGNs. Single torus models and combined torus-NLR models fail to fit the spectra of most sources but three component models adequately fit the spectra of all sources. We present torus inclination, cloud distribution, covering factor and torus mass for all sources and compare them with bolometric luminosity, black hole mass and accretion rate. The torus covering factor and mass are found to be correlated with the bolometric luminosity of the sources. We find that a substantial amount of the ~2-7 um radiation originates from a hot dust component, which likely situated in the innermost part of the torus. The luminosity radiated by this component and its covering factor are comparable to those of the torus. We quantify the emission by the NLR clouds and estimate their distance from the center. The distances are ~700 times larger than the dust sublimation radius and the NLR covering factor is about 0.07. The total covering factor by all components is in good agreement with the known AGN type-I:type-II ratio.