Probing the active galactic nucleus unified model torus properties in Seyfert galaxies

Abstract

We studied the physical parameters of a sample comprising of all Spitzer/Infrared Spectrograph public spectra of Seyfert galaxies in the mid-infrared (5.2–38 μm range) under the active galactic nucleus (AGN) unified model. We compare the observed spectra with ∼106 CLUMPY model spectral energy distributions, which consider a torus composed of dusty clouds. We find a slight difference in the distribution of line-of-sight inclination angle, i, requiring larger angles for Seyfert 2 (Sy 2) and a broader distribution for Seyfert 1 (Sy 1). We found small differences in the torus angular width, σ, indicating that Sy 1may host a slightly narrower torus than Sy 2. The torus thickness, together with the bolometric luminosities derived, suggests a very compact torus up to ∼6 pc from the central AGN. The number of clouds along the equatorial plane, N, as well the index of the radial profile, q, is nearly the same for both types. These results imply that the torus cloud distribution is nearly the same for type 1 and type 2 objects. The torus mass is almost the same for both types of activity, with values in the range of Mtor ∼ 104−107M . The main difference appears to be related to the clouds’ intrinsic properties: type 2 sources present higher optical depths τ V. The results presented here reinforce the suggestion that the classification of a galaxy may also depend on the intrinsic properties of the torus clouds rather than simply on their inclination. This is in contradiction with the simple geometric idea of the unification model.