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

By Cristina Ramos Almeida, N. Levenson, A. Alonso-Herrero, A. A. Ramos, J. M. R. Espinosa, A. M. García, C. Packham, R. Mason, J. Radomski, T. Díaz-Santos. 2011

145 citations recorded by the source corpus.

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 (Pesc = 0.05% ± 0.080.03%) than those of Seyfert 1 (CT = 0.5 ± 0.1; Pesc = 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.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/0faf74ff76bcda616e4424c9e2e275da26ecdbff

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In Astronomy and Astrophysics

1. P. Hopkins
2. H. Netzer
3. J. Fritz
4. Roger Davies
5. L. Tacconi
6. M. Stalevski
7. C. Ricci
8. Maarten Baes

In Instrumentation

1. J. Fritz
2. M. Stalevski
3. Maarten Baes
4. Roger Davies
5. L. Tacconi
6. Wolfgang J. Duschl
7. D. Asmus
8. M. Malkan

Citations in the corpus

• Molecular line emission in NGC 1068 imaged with ALMA: I. An AGN-driven outflow in the dense molecular gas (2014, methodology): “More specifically, these models reproduce the non-stellar NIR and MIR SEDs and MIR spectroscopy of local Seyfert galaxies (Ramos Almeida et al. 2009, 2011a; Hoenig et al. 2010; Alonso-Herrero et al. 2011; Lira et al. 2013) and PG quasars (Mor et al. 2009).”
• OUTFLOWS FROM ACTIVE GALACTIC NUCLEI: KINEMATICS OF THE NARROW-LINE AND CORONAL-LINE REGIONS IN SEYFERT GALAXIES, (2011, background): “Recently, Ramos-Almeida et al. (2011) fitted models of clumpy tori to the spectral energy distributions (SEDs) of seven intermediatetype Seyfert galaxies including NGC 4151, NGC 6814, and NGC 7469.”
• First X-ray-based statistical tests for clumpy-torus models: eclipse events from 230 years of monitoring of Seyfert AGN (2014, result): “Ramos Almeida et al. (2011) noted that the IR SEDs of Sy 1.8–1.9 AGN had spectral slopes intermediate between those of Sy 1.0–1.5s and Sy 2s, and noted similarities in SED fitting parameter results between the 1.8–1.9s and the 1.0–1.5s.”
• TORUS AND ACTIVE GALACTIC NUCLEUS PROPERTIES OF NEARBY SEYFERT GALAXIES: RESULTS FROM FITTING INFRARED SPECTRAL ENERGY DISTRIBUTIONS AND SPECTROSCOPY (2011, result): “See Asensio Ramos & Ramos Almeida (2009) for more details.”
• The dust covering factor in active galactic nuclei (2016, methodology): “…by fitting torus emission models to the spectral energy distributions (SEDs) of type 1 and type 2 AGNs (e.g. Fritz et al. 2006; Hatziminaoglou et al. 2009; Mor et al. 2009; Mor & Trakhtenbrot 2011; AlonsoHerrero et al. 2011; Ramos Almeida et al. 2011; Mor & Netzer 2012; Mateos et al. 2015, 2016).”
• ON THE UNIFICATION OF ACTIVE GALACTIC NUCLEI (2012, result): “Fitting of IR observations with clumpy torus models with Gaussian angular distributions has been reported by a number of teams, and figure 2 shows the results of these modeling efforts in the N0–σ plane together with the contour plots of CT.2 As expected from realistic unification, and first noted b”
• The subarcsecond mid-infrared view of local active galactic nuclei – II. The mid-infrared–X-ray correlation (2015, background): “Third, higher obscured objects could have on average higher covering factors (Ramos Almeida et al. 2011; Elitzur 2012), which could mitigate differences.”