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

Abstract

We quantify the luminosity contribution of active galactic nuclei (AGN) to the 12 µm, mid-infrared (MIR; 5-38 µm), and the total IR (5-1000 µm) 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 AGN and starburst components using AGN torus and star-forming galaxy templates. This enables us to recover the AGN torus emission also for lowluminosity end, down to log(L 14−150 /erg s −1 ) 41, which typically have significant host galaxy contamination. We find that the luminosity contribution of the AGN to the 12 µm, 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 µm. 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 above the AGN bolometric luminosity of log(L (AGN) bol /erg s −1 ) 42.5. 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.

Obscuring Fraction of Active Galactic Nuclei Implied by Supernova and Radiative Feedbacks

“…However, the covering factor observed in X-rays (Ichikawa et al 2019) is larger (f obs,X ) than our predictions for any L AGN , as shown in Fig. 10.…”

“…Here, we select 179 AGNs with M BH = 10 7.5 − 10 8.5 M ⊙ from the total of 587 objects in Ichikawa et al (2019). Figure 10 compares the observed data with the hybrid model (red solid line) and SN-driven turbulence model (red dashed line) with M BH = 10 8 M ⊙ , C * ,max = 10 −7 yr −1 , r in = 1 pc,τ = 10 and Σ g = Σ g,crtit ≃ 1.0 g cm −2 .…”

“…This kind of stratified structure may explain the dust deficient absorber. An alternative possibility is that the obscuring structures at optical/IR and X-ray bands are intrinsically different as shown in Figure 11 (b), i.e., the covering angle of the dust-free gas structure inside the dust sublimation radius is larger than that of the dusty CND (e.g., Merloni et al 2014;Davies et al 2015;Ichikawa et al 2019). If this is the case, the dust-free absorbers inside the dusty structure (< 1pc) would be an essential structure to determine the obscuring fraction (f obs,X ) for AGNs with low Eddington ratios of L AGN /L Edd < 10 −2 .…”

“…The dotted black line corresponds to the case of Σg = Σg,crit ≃ 3.0 g cm −2 . Comparison with IR observational data (blue symbols) and X-ray data (black symbols) of nearby AGNs (both IR and X-ray data fromIchikawa et al 2019) with the average BH mass ≃ 10 8 M⊙. The red solid line represents the prediction of the hybrid model (SN + radiation pressure model) with MBH = 10 8 M⊙, C * ,max = 10 −7 yr −1 , rin = 1 pc,τ = 10 and Σg = Σg,crtit ≃ 1.0 g cm −2 .…”

XCLUMPY: X-Ray Spectral Model from Clumpy Torus and Its Application to the Circinus Galaxy

“…In smooth tori, it is therefore expected that the ratio between the infrared and X-ray luminosities would be systematically higher in type 1 AGNs where inner parts of the torus are more visible. In reality, however, the correlations are very similar among type 1 and type 2 AGNs (Gandhi et al 2009;Ichikawa et al 2012Ichikawa et al , 2017Ichikawa et al , 2019Asmus et al 2015;Kawamuro et al 2016a).…”