Oral Presentation

BAT AGN Spectroscopic Survey (BASS): The Covering Factor of Dust and Gas in Swift/BAT AGN

Author(s): Kohei Ichikawa (Tohoku/Columbia) and BASS team

Presenter: Kohei Ichikawa (Tohoku University)

We quantify the luminosity contribution of active galactic nuclei (AGN) to the 12 um, mid-infrared (MIR; 5-38 um), and the total IR (5-1000 um) emission in the local AGN detected in the all-sky 70-month
Swift/Burst Alert Telescope (BAT) ultra-hard X-ray survey. We decompose the IR spectral energy distributions (SEDs) of 587 objects into the AGN and starburst components using AGN torus and star-forming galaxy templates. This enables us to recover the AGN torus emission including the low-luminosity end, down to log L(14-150keV)/erg s^-1 ~41, which typically have significant host galaxy contamination. The sample demonstrates that the luminosity contribution of the AGN to the 12 um, the MIR, and the total IR band 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 um. The obtained total IR AGN luminosity 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 of the dust covering factor is always smaller than that of the X-ray obscuration fraction. Considering that X-ray obscuration fraction is equivalent to the covering factor coming from both the dust and gas, it indicates that an additional neutral gas component, along with the dusty torus, is responsible for the absorption of X-ray emission.