Are the properties of the Unified Model obscuring torus expected to be the same for all AGN?
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| When |
2012-05-11 14:00
2012-05-11 15:00
2012-05-11 from 14:00 to 15:00 |
| Where | Cody Hall |
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Almudena Alonso-Herrero (Instituto de Fisica de Cantabria, CSIC-UC)
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.


