A mid-infrared statistical investigation of clumpy torus model predictions

Abstract

We present new calculations of the Clumpy AGN Tori in a 3D geometry (CAT3D) clumpytorus models, which now include a more physical dust sublimation model as well as activegalactic nucleus (AGN) anisotropic emission. These new models allow graphite grains topersist at temperatures higher than the silicate dust sublimation temperature. This producesstronger near-infrared emission and bluer mid-infrared (MIR) spectral slopes. We make astatistical comparison of the CAT3D model MIR predictions with a compilation of subarcsecondresolution ground-based MIR spectroscopy of 52 nearby Seyfert galaxies (mediandistance of 36 Mpc) and 10 quasars. We focus on the AGN MIR spectral index aMIR andthe strength of the 9.7 μm silicate feature S. As with other clumpy torus models, the newCAT3Dmodels do not reproduce the Seyfert galaxies with deep silicate absorption (S <-1).Excluding those, we conclude that the new CAT3D models are in better agreement with theobserved aMIR and S of Seyfert galaxies and quasars. We find that Seyfert 2 are reproducedwith models with low photon escape probabilities, while the quasars and the Seyfert 1-1.5require generally models with higher photon escape probabilities. Quasars and Seyfert 1-1.5tend to show steeper radial cloud distributions and fewer clouds along an equatorial line ofsight than Seyfert 2. Introducing AGN anisotropic emission besides the more physical dustsublimation models alleviates the problem of requiring inverted radial cloud distributions (i.e.more clouds towards the outer parts of the torus) to explain the MIR spectral indices of type 2 Seyferts.