BAT AGN Spectroscopic Survey. XI. the Covering Factor of Dust and Gas in Swift/BAT Active Galactic Nuclei

Kohei Ichikawa, Claudio Ricci, Yoshihiro Ueda, Franz E. Bauer, Taiki Kawamuro, Michael J. Koss, Kyuseok Oh, David J. Rosario, T. Taro Shimizu, Marko Stalevski, Lindsay Fuller, Christopher Packham, Benny Trakhtenbrot

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Abstract

We quantify the luminosity contribution of active galactic nuclei (AGNs) to the 12 μm, mid-infrared (MIR; 5-38 μm), and total IR (5-1000 μm) emission in the local AGNs detected in the all-sky 70 month Swift/Burst Alert Telescope (BAT) ultrahard X-ray survey. We decompose the IR spectral energy distributions (SEDs) of 587 objects into the AGN and starburst components using templates for an AGN torus and a star-forming galaxy. This enables us to recover the emission from the AGN torus including the low-luminosity end, down to log(L14-50/erg s-1) ≃ 41, which typically has significant host galaxy contamination. The sample demonstrates that the luminosity contribution of the AGN to the 12 μm, the MIR, and the total IR bands is an increasing function of the 14-150 keV luminosity. We also find that for the most extreme cases, the IR pure-AGN emission from the torus can extend up to 90 μm. The total IR AGN luminosity obtained through the IR SED decomposition enables us to estimate the fraction of the sky obscured by dust, i.e., the dust covering factor. We demonstrate that the median dust covering factor is always smaller than the median X-ray obscuration fraction above an AGN bolometric luminosity of log(L(AGN) bol/erg s-1) ≃ 42.5. Considering that the X-ray obscuration fraction is equivalent to the covering factor coming from both the dust and gas, this indicates that an additional neutral gas component, along with the dusty torus, is responsible for the absorption of X-ray emission.

Original languageEnglish
Article number31
JournalAstrophysical Journal
Volume870
Issue number1
DOIs
StatePublished - 1 Jan 2019

Funding

FundersFunder number
Building of Consortia for the Development of Human Resources in Science and Technology
CONI-CYT-ChilePFB-06/2007
Science and Technology Facilities CouncilST/ P000541/1
Japan Society for the Promotion of Science17F17321, 18K13584, 17K05384, 17J09016
Japan Science and Technology Agency
Fondo Nacional de Desarrollo Científico y Tecnológico1141218
Ministerio de Economía, Fomento y TurismoIC120009

    Keywords

    • galaxies: active
    • galaxies: nuclei
    • infrared: galaxies

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