Astron. Astrophys. 339, 687-692 (1998)

Near-IR images of the torus and micro-spiral structure in NGC 1068 using adaptive optics ^*

D. Rouan ¹, F. Rigaut ², D. Alloin ³, R. Doyon ⁴, O. Lai ¹, D. Crampton ⁵, E. Gendron ¹ and R. Arsenault <sup>2, 1

1</sup> Observatoire de Paris, Département Spatial, CNRS URA 264, F-92195 Meudon Cedex, France
² Canada-France-Hawaii Telescope corp., PO Box 1597, Kamuela, Hawaii, 96743, USA
³ Service d'Astrophysique, CNRS URA 2052, CE Saclay, F-91191 Gif-sur-Yvette, France
⁴ Université de Montréal - Département d'Astronomie, C.P. 6128, Succ. A, Montréal, H3C 3J7, Canada
⁵ Dominion Astrophysical Observatory, HIA, National Research Council of Canada, RR5 Victoria, V8X 4M6, Canada

Received 11 December 1997 / Accepted 15 June 1998

Abstract

We present diffraction-limited near-IR images in J, H and K of the nucleus of NGC 1068, obtained with the Adaptive Optics system Pueo at CFHT. The achieved resolution (0:0012) reveals several components, particularly prominent on the [J-K] image: a) an unresolved, conspicuous core (size 9 pc); b) an elongated structure at P.A. , beginning to show up at radius 15 pc; c) a S-shaped structure with radial extent 20 pc, including a bar-like central elongation at P.A. and two short spiral arms. A precise registration of the IR peak was carried out relative to the HST I-band peak. The K unresolved core is found to be close to the location of the putative central engine (radio source S1). Consistent with the Unified Model of AGN, the near-IR core is likely the emission from the hot inner walls of the dust/molecular torus. The extremely red colors of the 0:002 diameter core, [J-K]=7.0, [H-K]=3.8, lead to an intrinsic extinction A_V 25, assuming classical dust grains at 1500 K.

The elongated structure at P.A. may trace the presence of cooler dust within and around the torus. This interpretation is supported by two facts at least: a) the elongated structure is perpendicular to the local radio jet originating at S1; b) its direction follows exactly that of the disk of ionized gas recently found with the VLBA. Regarding the S-shaped feature, the near-IR flux of the bar-like central elongation at P.A.= , if interpreted in terms of free-free emission from ionized gas, is roughly consistent with the level of 5 GHz emission. However, the radio spectrum behaviour is indicative of synchrotron emission and we rather interpret the 2.2 µm emission as originating from warm dust in the shaded part of NLR clouds or in stellar photospheres. The shape itself suggests an extremely compact barred spiral structure, that would be the innermost of a series of nested spiral structures, as predicted by models and simulations. This is supported by the inner stellar distribution - deduced from the J image - which clearly follows an exponential disk with a 19 pc scale-length, precisely that expected from the rotation of a bar twice this size.

Key words: galaxies: active galaxies: individual NGC 1068 galaxies: Seyfert

* Based on observations obtained at Canada-France-Hawaii Telescope operated by the National Research Council of Canada, The Centre National de la Recherche Scientifique de France and the University of Hawaii

Send offprint requests to: D. Rouan (rouan@obspm.fr)

SIMBAD Objects

Contents

• 1. Introduction
• 2. Observations and results
  • 2.1. Photometry of the inner core
  • 2.2. Large and small scale spiral structures
  • 2.3. Relative positioning of the near-IR and visible peaks
• 3. Discussion and conclusion
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: October 22, 1998
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