An original interferometric study of NGC 1068 with VISIR BURST mode images^*

¹ LUTH, Observatoire de Paris, 92195 Meudon Cedex, France e-mail: anne.poncelet@obspm.fr
² LESIA, Observatoire de Paris, 92195 Meudon Cedex, France
³ CEA/DSM/DAPNIA/Service d'Astrophysique, CE Saclay, 91191 Gif-sur-Yvette, France

Received: 22 December 2006
Accepted: 22 June 2007

Abstract

Context.We present 12.8 μm images of the core of NGC 1068, the archetype Seyfert type II galaxy, obtained during first operations of the BURST mode of the VLT/VISIR (Imager and Spectrometer in the InfraRed at the Very Large Telescope).

Aims.We trace structures under the diffraction limit of one UT (Unit Telescope at the VLT) and we investigate the link between dust in the vicinity of the central engine of NGC 1068, recently resolved by interferometry with MIDI (Mid-InfrareD Interferometer), and more extended structures. This step is mandatory for a multi-scale understanding of the sources of mid-infrared emission in active galactic nuclei (AGN).

Methods.A speckle processing of VISIR BURST mode images was performed to extract very low spatial-frequency visibilities, first considering the full field of VISIR BURST mode images and then limiting it to the mask used for the acquisition of MIDI data.

Results.Extracted visibilities are reproduced with a multi-component model. We identify two major sources of emission at 12.8 μm: a compact one <85 mas, directly associated with the dusty torus, and an elliptical one of size (<140) mas  1187 mas and PA ~ –4° (from north to east), which gives a new description of the NS elongation of the nucleus. This is consistent with previous deconvolution processes. The combination with MIDI data reveals the close environment of the dusty torus to contribute to ~83% of the MIR flux seen by MIDI.

Conclusions.This strong contribution has to be considered in modeling long baseline interferometric data. It must be related to the NS elongated component which is thought to originate from individually unresolved dusty clouds located inside the ionization cone wich are photoevaporating and radiatively accelerated. Low temperatures of the dusty torus are not challenged, emphasizing the scenarios of clumpy torus.