Loading…

Testing the Unification Model for Active Galactic Nuclei in the Infrared: Are the Obscuring Tori of Type 1 and 2 Seyferts Different?

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...

Full description

Saved in:
Bibliographic Details
Published in:The Astrophysical journal 2011-04, Vol.731 (2), p.92-jQuery1323909271255='48'
Main Authors: 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
Format: Article
Language:English
Subjects:
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary: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.
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/731/2/92