Mid and Far Infrared Properties of a Complete Sample of Local AGNs

TL;DR

This study examines the infrared properties of local AGNs, revealing a strong correlation between X-ray and MIR luminosities, indicating hot dust emission dominance and isotropic infrared emission, with starburst activity in obscured AGNs.

Contribution

It provides the first comprehensive analysis of MIR to FIR properties of a complete local AGN sample, highlighting the correlation with X-ray luminosity and the nature of infrared emission.

Findings

Strong correlation between hard X-ray and MIR luminosities.

Infrared emission is isotropic, supporting clumpy dust torus models.

Obscured AGNs show PAH features indicating starburst activity.

Abstract

We investigate the mid- (MIR) to far-infrared (FIR) properties of a nearly complete sample of local Active Galactic Nuclei (AGNs) detected in the Swift/BAT all sky hard X-ray (14-195 keV) survey, based on the cross correlation with the AKARI infrared survey catalogs complemented by those with IRAS and WISE. Out of 135 non-blazer AGNs in the Swift/BAT 9 month catalog, we obtain the MIR photometric data for 128 sources either in the 9, 12, 18, 22, and/or 25 um band. We find good correlation between their hard X-ray and MIR luminosities over 3 orders of magnitude (42< log lambda L_{lambda}(9, 18 um)< 45), which is tighter than that with the FIR luminosities at 90 um. This suggests that thermal emission from hot dusts irradiated by the AGN emission dominate the MIR fluxes. Both X-ray unabsorbed and absorbed AGNs follow the same correlation, implying isotropic infrared emission, as expected in clumpy dust tori rather than homogeneous ones. We find excess signals around 9 um in the averaged infrared spectral energy distribution from heavy obscured "new type" AGNs with small scattering fractions in the X-ray spectra. This could be attributed to the PAH emission feature, suggesting that their host galaxies have strong starburst activities.