Probing the Active Galactic Nuclei Unified Model Torus Properties in Seyfert Galaxies

TL;DR

This study analyzes the properties of dusty tori in Seyfert galaxies using infrared spectra and compares them with clumpy torus models, revealing that intrinsic cloud properties influence galaxy classification beyond simple orientation effects.

Contribution

It provides a detailed comparison of observed spectra with clumpy torus models, highlighting the role of cloud properties in AGN classification, challenging the traditional unification model.

Findings

Seyfert 1 and 2 tori have similar cloud distributions and masses.

Type 2 clouds exhibit higher optical depths, affecting classification.

Torus sizes are compact, up to about 6 parsecs from the AGN.

Abstract

We studied the physical parameters of a sample comprising of all Spitzer/IRS public spectra of Seyfert galaxies in the mid-infrared (5.2-38$\mu$m range) under the active galactic nuclei (AGN) unified model. We compare the observed spectra with $\sim10^6$ 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 (Sy2) and a broader distribution for Seyfert 1 (Sy1). We found small differences in the torus angular width, $\sigma$, indicating that Sy1 may host a slightly narrower torus than Sy2. The torus thickness, together with the bolometric luminosities derived, suggest a very compact torus up to $\sim$6 pc from the central AGN. The number of clouds along the equatorial plane, $N$, as well the index of the radial profile, $q$, are 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 $M_{tor}\sim$10$^{4}-$10$^{7}\rm M_{\odot}$. The main difference appears to be related to the clouds' intrinsic properties: type 2 sources present higher optical depths $\tau_V$. The results presented here reinforce the suggestion that the classification of a galaxy may depend also 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.