Bibcode
Ramos-Almeida, C.; Levenson, N. A.; Alonso-Herrero, A.; Asensio-Ramos, A.; Rodríguez-Espinosa, J. M.; Pérez-García, A. M.; Packham, C.; Mason, R.; Radomski, J. T.; Díaz-Santos, T.
Bibliographical reference
The Astrophysical Journal, Volume 731, Issue 2, article id. 92 (2011).
Advertised on:
4
2011
Journal
Citations
182
Refereed citations
165
Description
We present new mid-infrared imaging data for three Type-1 Seyfert
galaxies obtained with T-ReCS on the Gemini-South Telescope at
subarcsecond resolution. Our aim is to enlarge the sample studied in a
previous work to compare the properties of Type-1 and Type-2 Seyfert
tori using clumpy torus models and a Bayesian approach to fit the
infrared (IR) nuclear spectral energy distributions. Thus, the sample
considered here comprises 7 Type-1, 11 Type-2, and 3 intermediate-type
Seyferts. The unresolved IR emission of the Seyfert 1 galaxies can be
reproduced by a combination of dust heated by the central engine and
direct active galactic nucleus (AGN) emission, while for the Seyfert 2
nuclei only dust emission is considered. These dusty tori have physical
sizes smaller than 6 pc radius, as derived from our fits. Unification
schemes of AGN account for a variety of observational differences in
terms of viewing geometry. However, we find evidence that strong
unification may not hold and that the immediate dusty surroundings of
Type-1 and Type-2 Seyfert nuclei are intrinsically different. The Type-2
tori studied here are broader, have more clumps, and these clumps have
lower optical depths than those of Type-1 tori. The larger the covering
factor of the torus, the smaller the probability of having a direct view
of the AGN, and vice versa. In our sample, Seyfert 2 tori have larger
covering factors (CT = 0.95 ± 0.02) and smaller escape
probabilities (P esc = 0.05% ± 0.08
0.03%) than those of Seyfert 1 (CT = 0.5 ±
0.1; P esc = 18% ± 3%). All the previous differences
are significant according to the Kullback-Leibler divergence. Thus, on
the basis of the results presented here, the classification of a Seyfert
galaxy as a Type-1 or Type-2 depends more on the intrinsic properties of
the torus rather than on its mere inclination toward us, in
contradiction with the simplest unification model.
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