TORUS AND ACTIVE GALACTIC NUCLEUS PROPERTIES OF NEARBY SEYFERT GALAXIES: RESULTS FROM FITTING INFRARED SPECTRAL ENERGY DISTRIBUTIONS AND SPECTROSCOPY

By A. Alonso-Herrero, C. Ramos Almeida, R. Mason, A. Asensio Ramos, P. Roche, N. Levenson, M. Elitzur, C. Packham, J. M. Rodríguez Espinosa, S. Young and 2 more. 2011

166 citations recorded by the source corpus.

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 N0. 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, Pesc ∼ 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 Lbol(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 Lbol(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 (f2 ∼ 0.1–0.3) at high AGN luminosities than at low AGN luminosities (f2 ∼ 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.

Subfields: Astronomy and Astrophysics, Instrumentation

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In Astronomy and Astrophysics

1. H. Netzer
2. C. Ricci
3. D. M. Alexander
4. Poshak Gandhi
5. L. Tacconi
6. Daniel Stern
7. M. Brightman
8. R. Nikutta

In Instrumentation

1. H. Netzer
2. C. Ricci
3. Daniel Stern
4. L. Tacconi
5. S. García-Burillo
6. A. Alonso-Herrero
7. A. Eckart
8. S. Aalto

Citations in the corpus

• First X-ray-based statistical tests for clumpy-torus models: eclipse events from 230 years of monitoring of Seyfert AGN (2014, background): “Alonso-Herrero et al. (2011), with the same approach but different sources, find τV = 105–146 (type Is) and 49–130 (type IIs).”
• The subarcsecond mid-infrared view of local active galactic nuclei – I. The N- and Q-band imaging atlas (2013, methodology): “Numerous previous works have performed SED fitting to test various torus models (e.g., Ramos Almeida et al. 2009; Alonso-Herrero et al. 2011; Lira et al. 2013), and they have emphasized the importance of the 5µm flux.”
• New Spectral Model for Constraining Torus Covering Factors from Broadband X-Ray Spectra of Active Galactic Nuclei (2018, background): “A tentative trend for lower covering factors at higher luminosity was also found from analyses of individual AGN both in the infrared (Alonso-Herrero et al. 2011) and in the X-ray band (Brightman et al. 2015).”
• Revisiting the Unified Model of Active Galactic Nuclei (2015, background): “A detailed comparison of large and small aperture spectroscopic observations is given in Alonso-Herrero et al. (2011) and Lira et al. (2013).”
• Molecular line emission in NGC 1068 imaged with ALMA: I. An AGN-driven outflow in the dense molecular gas (2014, methodology): “Alonso-Herrero et al. (2011) fitted the nuclear NIR and MIR SED and MIR spectroscopy of NGC 1068 using the so-called CLUMPY torus models of Nenkova et al. (2008a, 2008b).”