AKARI infrared camera observations of the 3.3 μm PAH feature in Swift/BAT AGNs

We explore the relationships between the 3.3μm polycyclic aromatic hydrocarbon (PAH) feature and active galactic nucleus (AGN) properties of a sample of 54 hard X-ray selected bright AGNs, including both Seyfert1 and Seyfert2 type objects, using the InfraRed Camera (IRC) on board the infrared astronomical satellite AKARI. The sample is selected from the nine-month Swift/BAT survey in the 14-195 keV band and all of them have measured X-ray spectra at E 10keV. These X-ray spectra provide measurements of the neutral hydrogen column density (N_H) towards the AGNs. We use the 3.3μm PAH luminosity (L_3.3μm) as a proxy for star-formation activity and hard X-ray luminosity (L_14-195keV) as an indicator of the AGN activity. We search for possible differences in star-formation activity between type1 (unabsorbed) and type2 (absorbed) AGNs. We have made several statistical analyses taking the upper limits of the PAH lines into account utilizing survival analysis methods. The results of our log(L_14-195keV) versus log(L_3.3μm) regression show a positive correlation and the slope for the type1/unobscured AGNs is steeper than that of type2/obscured AGNs at a 3σ level. Our analysis also shows that the circumnuclear star formation is more enhanced in type2/absorbed AGNs than type1/unabsorbed AGNs for low X-ray luminosity/low Eddington ratio AGNs, while there is no significant dependence of star-formation activities on the AGN type in the high X-ray luminosities/Eddington ratios.