Leiden Observatory, Leiden University,
PO Box 9513
2 Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, Gießenbachstr., 85741 Garching, Germany
3 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
4 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
Accepted: 13 January 2014
Aims. The aim of this paper is to understand the relation in active galactic nuclei (AGNs) between the small obscuring torus and dusty structures at larger scales (5−10 pc).
Methods. The dusty structures in AGNs are best observed in the mid-infrared. To achieve the necessary spatial resolution (20−100 millarcsec) we use ESO’s Mid-Infrared Interferometer (MIDI) with the 1.8 m Auxiliary Telescopes. We use the chromatic phases in the data to improve the spatial fidelity of the analysis.
Results. We present interferometric data for NGC 1068 obtained in 2007 and 2012. We find no evidence of source variability. Many (u,v) points show non-zero chromatic phases indicating significant asymmetries. Gaussian model fitting of the correlated fluxes and chromatic phases provides a three-component best fit with estimates of sizes, temperatures, and positions of the components. A large, warm, offcenter component is required at a distance approximately 90 mas to the northwest at a position angle (PA) of ~−18°.
Conclusions. The dust at 5−10 pc in the polar region contributes four times more to the mid-infrared flux at 12 μm than the dust located at the center. This dust may represent the inner wall of a dusty cone. If similar regions are heated by the direct radiation from the nucleus, then they will contribute substantially to the classification of many Seyfert galaxies as Type 2. Such a region is also consistent in other Seyfert galaxies (the Circinus galaxy, NGC 3783, and NGC 424).
Key words: techniques: interferometric / galaxies: active / galaxies: nuclei / galaxies: Seyfert / galaxies: individual: NGC 1068 / radiation mechanisms: thermal
Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme IDs 080.B-0928 and 089.B-0099. Based on data obtained from the ESO Science Archive Facility.
Appendices are available in electronic form at http://www.aanda.org
The reduced visibilities (UVFITS tables) are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (220.127.116.11) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/565/A71
© ESO, 2014