TESTING THE UNIFICATION MODEL FOR ACTIVE GALACTIC NUCLEI IN THE INFRARED: ARE THE OBSCURING TORI OF TYPE 1 AND 2 SEYFERTS DIFFERENT?

Journal Article · Wed Apr 20 04:00:00 EDT 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/731/2/92· OSTI ID:21574710

Ramos Almeida, C ^[1]; Levenson, N A; Radomski, J T ^[2]; Alonso-Herrero, A ^[3]; Asensio Ramos, A; Rodriguez Espinosa, J M; Perez Garcia, A M ^[4]; Packham, C ^[5]; Mason, R ^[6]; DIaz-Santos, T ^[7]

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1. Department of Physics and Astronomy, University of Sheffield, S3 7RH (United Kingdom)
2. Gemini Observatory, Casilla 603, La Serena (Chile)
3. Centro de Astrobiologia, INTA-CSIC, E-28850 Madrid (Spain)
4. Instituto de Astrofisica de Canarias (IAC), C/VIa Lactea, s/n, E-38205 La Laguna, Tenerife (Spain)
5. Astronomy Department, University of Florida, 211 Bryant Space Science Center, P.O. Box 112055, Gainesville, FL 32611-2055 (United States)
6. Gemini Observatory, Northern Operations Center, 670 North Aohoku Place, Hilo, HI 96720 (United States)
7. Department of Physics, University of Crete, GR-71003 Heraklion (Greece)

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 (C{sub T} = 0.95 {+-} 0.02) and smaller escape probabilities (P{sub esc} = 0.05% {+-} {sup 0.08}{sub 0.03}%) than those of Seyfert 1 (C{sub T} = 0.5 {+-} 0.1; P{sub 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.

• OSTI ID: 21574710
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 731; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
DUSTS
EMISSION
ENERGY SPECTRA
GALAXIES
GALAXY NUCLEI
SEYFERT GALAXIES
SPECTRA
TORI