Bibcode
Alonso-Herrero, Almudena; Ramos Almeida, Cristina; Mason, Rachel; Asensio-Ramos, A.; Roche, Patrick F.; Levenson, Nancy A.; Elitzur, Moshe; Packham, Christopher; Rodríguez-Espinosa, J. M.; Young, Stuart; Díaz-Santos, Tanio; Pérez-García, A. M.
Bibliographical reference
The Astrophysical Journal, Volume 736, Issue 2, article id. 82 (2011).
Advertised on:
8
2011
Journal
Citations
202
Refereed citations
184
Description
We used the CLUMPY torus models and a Bayesian approach to fit the
infrared spectral energy distributions and ground-based high angular
resolution mid-infrared spectroscopy of 13 nearby Seyfert galaxies. This
allowed us to put tight constraints on torus model parameters such as
the viewing angle i, the radial thickness of the torus Y, the angular
size of the cloud distribution σtorus, and the average
number of clouds along radial equatorial rays N 0. We found
that the viewing angle i is not the only parameter controlling the
classification of a galaxy into type 1 or type 2. In principle, type 2s
could be viewed at any viewing angle i as long as there is one cloud
along the line of sight. A more relevant quantity for clumpy media is
the probability for an active galactic nucleus (AGN) photon to escape
unabsorbed. In our sample, type 1s have relatively high escape
probabilities, P esc ~ 12%-44%, while type 2s, as expected,
tend to have very low escape probabilities. Our fits also confirmed that
the tori of Seyfert galaxies are compact with torus model radii in the
range 1-6 pc. The scaling of the models to the data also provided the
AGN bolometric luminosities L bol(AGN), which were found to
be in good agreement with estimates from the literature. When we
combined our sample of Seyfert galaxies with a sample of PG quasars from
the literature to span a range of L bol(AGN) ~
1043-1047 erg s-1, we found plausible
evidence of the receding torus. That is, there is a tendency for the
torus geometrical covering factor to be lower (f 2 ~ 0.1-0.3)
at high AGN luminosities than at low AGN luminosities (f 2 ~
0.9-1 at ~1043-1044 erg s-1). This is
because at low AGN luminosities the tori appear to have wider angular
sizes (larger σtorus) and more clouds along radial
equatorial rays. We cannot, however, rule out the possibility that this
is due to contamination by extended dust structures not associated with
the dusty torus at low AGN luminosities, since most of these in our
sample are hosted in highly inclined galaxies.
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