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Are the properties of the Unified Model obscuring torus expected to be the same for all AGN?

The Unified Model for active galactic nuclei (AGN) proposes the ubiquitous presence of an obscuring torus around their nuclei, with type 1 and type 2 AGN being intrinsically similar. The central region of an AGN is obscured when viewed along directions close to the equatorial plane of the torus and is classified as a type 2, while in type 1 there is a direct view of the AGN. In this talk I will discuss the properties of the torus of a sample of nearby Seyfert galaxies. We used the Nenkova et al. (2008) clumpy torus models and a Bayesian approach to fit their nuclear infrared (IR) spectral energy distributions (SEDs) and mid-IR spectroscopy to put constraints on the torus models parameters. The clumpy torus models produce good fits to the data and confirm that the tori of Seyfert galaxies are small (a few pc), in agreement with results from mid-IR interferometry. As expected, in a clumpy medium type 1s have relatively high probabilities for an AGN-produced photon to escape unabsorbed, while type 2s have very low escape probabilities. We find, however, that the torus properties may not be universal. In particular we find evidence of the so-called receding torus. In this scenario the higher fraction of type 1 AGN at high AGN luminosities is explained as a decreasing covering factor of the torus. Our results seem to indicate that the tori of high luminosity AGN (mostly type 1s in our sample) contain fewer clouds along equatorial rays and have smaller opening angles which result in decreased covering factors. I will also present new results from our on-going mid-IR survey of nearby AGN using the CanariCam instrument on the 10.4m Gran Telescopio Canarias.

Cody Hall

Almudena Alonso-Herrero (Instituto de Fisica de Cantabria, CSIC-UC)

May 11, 2012
14:00 - 15:00