Revealing the large nuclear dust structures in NGC 1068 with MIDI/VLTI^{⋆,⋆⋆,⋆⋆⋆}

¹ Leiden Observatory, Leiden University, PO Box 9513 2300 RA Leiden The Netherlands
e-mail: nlopez@strw.leidenuniv.nl
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

Received: 7 November 2013
Accepted: 13 January 2014

Abstract

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).