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Astron. Astrophys. 353, 465-472 (2000)

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Adaptive optics images at 3.5 and 4.8 µm of the core arcsec of NGC 1068: more evidence for a dusty/molecular torus *

O. Marco and D. Alloin

European Southern Observatory (ESO), Casilla 19001, Santiago 19, Chile

Received 30 March 1999 / Accepted 27 August 1999

Abstract

Adaptive optics observations of NGC 1068 have allowed us to reach with a 4 m class telescope, diffraction-limited images at 3.5µm (FWHM=0.24") and 4.8µm (FWHM=0.33") of the central arcsec region. These observations reveal the presence of an unresolved core (radius less than 8 pc at Half Maximum) and an 80 pc sized "disc-like" structure at P.A. [FORMULA] 100o, which is interpreted as the dusty/molecular torus invoked in the AGN unification scheme. They show as well an extended emission region along the NNE-SSW direction, of 100 pc full size, most probably associated with dust in the NLR. The position of the unresolved core at 3.5 and 4.8µm is found to be coincident with that of the core observed at 2.2µm and outlines the location of the central engine in the AGN of NGC 1068 . Considering as well previous AO observations at 2.2µm we infer that there must exist a very steep gradient of the dust grain temperature, close to the central engine. At a distance of 30 pc from the central heating source, the dust grain temperature deduced from the [L-M] color is found to be [FORMULA] 500 K. The mass of warm dust ([FORMULA]500 K) in the 0.6" diameter core is found to be [FORMULA] 0.5 [FORMULA]. The spectral energy distribution from 1 to 10µm is provided for the 0.6" diameter core. These results are briefly discussed in the context of current torus models.

Key words: galaxies: individual: NGC 1068 – galaxies: Seyfert – galaxies: nuclei – infrared: galaxies – galaxies: active – instrumentation: adaptive optics

* Based on observations collected at the European Southern Observatory, La Silla, Chile.

Send offprint requests to: O. Marco

Correspondence to: omarco@eso.org

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© European Southern Observatory (ESO) 2000

Online publication: December 17, 1999
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