The current unification scheme for Active Galactic Nuclei (herefater AGN) postulates the existence of a thick molecular/dusty torus surrounding a black-hole/accretion-disc system (see, e.g. Krolik 1999). Attempts to unveil this torus in a nearby AGN like NGC 1068 have drawn considerable effort on the side of high spatial resolution imaging, in particular in the near-IR (Chelli et al. 1987, Gallais, 1991, Young et al. 1996, Marco et al. 1997, Thatte et al. 1997, Rouan et al. 1998, Alloin et al. 1999, Wittkowski et al. 1998, Weinberger et al. 1999, Marco & Alloin, 2000) and mid-IR (Braatz et al. 1993, Cameron et al. 1993, Bock et al. 1998, Lumsden et al. 1999). With respect to the presence of such a torus, the most compelling results are: (a) VLBA 8 GHz data (Gallimore et al. 1997) revealing a 1 pc elongated distribution of ionized gas at PA 110o (the inner "hot zone" of the torus?), (b) adaptive optics (AO) observations at 2.2 µm (Rouan et al. 1998) showing extended emission along PA 102o and up to a 15 pc radius (in addition to a prominent unresolved core with size less that 9 pc and in addition to another 20 pc radius extended emission along PA 15o which follows the Narrow Line Region) and at 3.5 and 4.8 µm (Marco & Alloin, 2000) revealing structures similar in shape/orientation and on comparable scales, (c) near- and mid-IR imaging polarimetry (Lumsden et al. 1999) calling for the presence of hot and warm dust components fully consistent with those detected with AO. The structure elongated at PA 102o could trace the equatorial plane of an inclined dusty/molecular torus, from its inner walls of ionized material seen in radio, to its outer parts of thermally emitting dust with a temperature range from T 1500 K (dust sublimation temperature) to a few 100 K.
Models by Krolik & Begelman (1986), Pier & Krolik (1993), Efstathiou & Rowan-Robinson (1994), Granato & Danese (1994), and Granato et al. (1997) have explored torus sizes from 1 to 100 pc. They predict emission in the near-IR and mid-IR and provide high resolution model-maps at various wavelengths. Therefore, it is particularly timely to obtain high resolution mid-IR images to compare with model-maps.
Here, we present and discuss new results from diffraction-limited images obtained with the CFHT/Hawaii and ESO/La Silla 3.6m telescopes, at 11.2 and 20.5 µm respectively. Hereafter, the distance used for NGC1068 is 14.4 Mpc, leading to the equivalence 1" 70 pc in the object.
© European Southern Observatory (ESO) 2000
Online publication: December 5, 2000