A mid-infrared statistical investigation of clumpy torus model predictions

J. García-González, A. Alonso-Herrero, S. F. Hönig, A. Hernán-Caballero, C. Ramos Almeida, N. A. Levenson, P.F. Roche, O. González-Martín, C. Packham, M. Kishimoto. 2017. A mid-infrared statistical investigation of clumpy torus model predictions. Monthly Notices of the Royal Astronomical Society, 470, 3, 2578-2598 DOI: 10.1093/mnras/stx1361

We present new calculations of the Clumpy AGN Tori in a 3D geometry (CAT3D) clumpy torus models, which now include a more physical dust sublimation model as well as active galactic nucleus (AGN) anisotropic emission. These new models allow graphite grains to persist at temperatures higher than the silicate dust sublimation temperature. This produces stronger near-infrared emission and bluer mid-infrared (MIR) spectral slopes. We make a statistical comparison of the CAT3D model MIR predictions with a compilation of subarcsecond resolution ground-based MIR spectroscopy of 52 nearby Seyfert galaxies (median distance of 36 Mpc) and 10 quasars. We focus on the AGN MIR spectral index alpha(MIR) and the strength of the 9.7 mu m silicate feature S-Sil. As with other clumpy torus models, the new CAT3D models do not reproduce the Seyfert galaxies with deep silicate absorption (S-Sil < -1). Excluding those, we conclude that the new CAT3D models are in better agreement with the observed alpha(MIR) and S-Sil of Seyfert galaxies and quasars. We find that Seyfert 2 are reproduced with models with low photon escape probabilities, while the quasars and the Seyfert 1-1.5 require generally models with higher photon escape probabilities. Quasars and Seyfert 1-1.5 tend to show steeper radial cloud distributions and fewer clouds along an equatorial line of sight than Seyfert 2. Introducing AGN anisotropic emission besides the more physical dust sublimation 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.

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