Investigating the Covering Fraction Distribution of Swift/BAT AGNs with X-Ray and Infrared Observations

Abstract

We present an analysis of a sample of 69 local obscured Swift/Burst Alert Telescope active galactic nuclei (AGNs) with X-ray spectra from NuSTAR and infrared (IR) spectral energy distributions from Herschel and WISE. We combine this X-ray and IR phenomenological modeling and find a significant correlation between reflected hard X-ray emission and IR AGN emission, with suggestive indications that this correlation may be stronger than the one between intrinsic hard X-ray and IR emissions. This relation between the IR and reflected X-ray emission suggests that both are the result of the processing of intrinsic emission from the corona and accretion disk by the same structure. We explore the resulting implications on the underlying distribution of covering fraction for all AGNs, by generating mock observables for the reflection parameter and IR luminosity ratio using empirical relations found for the covering fraction with each quantity. We find that the observed distributions of the reflection parameter and IR-to-X-ray ratio are reproduced with broad distributions centered around covering fractions of at least ∼ 40%−50%, whereas narrower distributions match our observations only when centered around covering fractions of ∼ 70% − 80%. Our results are consistent with both independent estimates of the covering fractions of individual objects and the typical covering fraction obtained on the basis of obscured fractions for samples of AGNs. These results suggest that the level of reprocessing in AGNs, including X-ray reflection, is related in a relatively straightforward way to the geometry of the obscuring material.

State-of-the-art AGN SEDs for photoionization models: BLR predictions confront the observations

“…The cloud covering factor given in Table 1 decreases as the Eddington ratio increases. The consequences of changing covering factors have been discussed by, among many others, Oh et al (2015), Lanz et al (2019) and Lusso et al (2013). The low Eddington ratio objects require covering factors around 50%, with the covering factor decreasing to ∼ 5% for the highest Eddington ratio case.…”

The Evolution of the Interstellar Medium in Post-starburst Galaxies

“…10 Here τ burst is fixed to 25 Myr. package to calculate the Spearman's rank correlation (Isobe et al 1986;Lavalley et al 1992), and perform bootstrap analysis (1000 samples) to derive the confidence intervals of the Spearman correlation coefficient and the null hypothesis probability (Lanz et al 2019). The null hypothesis is that there is no monotonic relation between two parameters.…”

The evolving X-ray spectrum of active galactic nuclei: evidence for an increasing reflection fraction with redshift

“…An alternative approach, recently pursued by Ananna et al (2019), considers a small number of fixed AGN spectral models, but modifies the HXLF in order to fit the X-ray survey data. While it is important that the measured HXLFs be continuously improved, the observed increase in f 2 (e.g., Liu et al 2017), the connection between N H and R (e.g., Lanz et al 2019), and the increasing evidence for fundamental physical connections between the AGN and its environment (e.g., Ricci et al 2017), all strongly suggest that the observed AGN X-ray SED will be functions of both redshift and luminosity that should be considered in future XRB synthesis models.…”

“…Instead, these results imply that AGNs that are seen through moderate-to-heavy amounts of obscuration exist in fundamentally different environments than those observed through lower N H columns, and are therefore probing different AGN populations (Draper & Ballantyne 2010;Buchner et al 2015). The direct fitting of nearby Swift-BAT AGNs by Lanz et al (2019) also found that more obscured objects have larger R, although the analysis of Ricci et al (2017) gave the opposite conclusion which could be explained by modeling degeneracies (see Lanz et al 2019). The combination of an increasing f 2 with z and a correlation of R with N H provides a physical template for the redshift evolution in R that is needed to fit the NuSTAR number counts.…”

“…1, the reflection spectrum in faint AGNs likely originates from reprocessing in the distant gas responsible for AGN obscuration. Recently, Lanz et al (2019) highlighted the direct connection between R and the obscuring gas in a sample of Swift-BAT AGNs by finding a correlation between the reflected Xray luminosity (measured by NuSTAR) and the IR luminosity (measured by WISE and Herschel). This result clearly indicates that the X-ray, optical and UV radiation produced by the inner accretion disk is reprocessed by a common structure.…”