MODELING THE NUCLEAR INFRARED SPECTRAL ENERGY DISTRIBUTION OF TYPE II ACTIVE GALACTIC NUCLEI

We present results from model fitting to the spectral energy distribution (SED) of a homogeneous sample of Seyfert II galaxies drawn from the 12 mu m Galaxy Sample. Imaging and nuclear flux measurements are presented in an accompanying paper. Here we add Spitzer/IRS observations to further constrain the SEDs after careful subtraction of a starburst component. We use the library of CLUMPY torus models from Nenkova et al. and also test the two-phase models recently produced by Stalevski et al. We find that photometric and spectroscopic observations in the mid-IR (lambda greater than or similar to 5 mu m) are crucial to properly constrain the best-fit torus models. About half of our sources show clear near-IR excess of their SEDs above the best-fit models. This problem can be less severe when using the Stalevski et al. models. The nature of this emission is not clear since best-fitted blackbody temperatures are very high (similar to 1700-2500 K) and the Type II classification of our sources would correspond to a small probability to peer directly into the hottest regions of the torus. Crucially, the derived torus parameters are quite robust when using CLUMPY models, independently of whether or not the sources require an additional blackbody component. Our findings suggest that tori are characterized by N-0 greater than or similar to 5, sigma less than or similar to 40, tau less than or similar to 25, angle i greater than or similar to 40 degrees, Y less than or similar to 50, and A(v)(los) similar to 100-300, where N-0 is the number of clouds in the equatorial plane of the torus, sigma is the characteristic opening angle of the cloud distribution, tau is the opacity of a single cloud, angle i is the line-of-sight orientation of the torus, Y is the ratio of the inner to the outer radii, and A(v)(los) is the total opacity along the line of sight. From these, we can determine typical torus sizes and masses of 0.1-5.0 pc and 10(4)-10(6)M(circle dot), respectively. We find tentative evidence that those nuclei with detected hidden broad-line regions are characterized by lower levels of extinction than those without one. Finally, we find no correlation between the torus properties and the presence of circumnuclear or more global star formation.