Astronomy & Astrophysics

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Issue		A&A Volume 425, Number 1, October I 2004
Page(s)		77 - 87
Section		Extragalactic astronomy
DOI		10.1051/0004-6361:20040362

A&A 425, 77-87 (2004)
DOI: 10.1051/0004-6361:20040362

Diffraction-limited bispectrum speckle interferometry of the nuclear region of the Seyfert galaxy NGC 1068 in the H and K ' bands

G. Weigelt¹, M. Wittkowski², Y. Y. Balega³, T. Beckert¹, W. J. Duschl⁴, K.-H. Hofmann¹, A. B. Men'shchikov⁵ and D. Schertl¹

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: weigelt@mpifr-bonn.mpg.de
² European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
³ Special Astrophysical Observatory, Nizhnij Arkhyz, Zelenchuk region, Karachai-Cherkesia 357147, Russia
⁴ Institut für Theoretische Astrophysik der Universität Heidelberg, Tiergartenstraße 15, 69121 Heidelberg, Germany
⁵ Institute for Computational Astrophysics, Saint Mary's University, Halifax, NS B3H 3C3, Canada

(Received 1 March 2004 / Accepted 4 June 2004 )

Abstract
We present near-infrared bispectrum speckle interferometry studies of the nuclear region of the Seyfert 2 galaxy NGC 1068 . A diffraction-limited K'-band image with 74 mas resolution and the first H-band image with 57 mas resolution were reconstructed from speckle interferograms obtained with the SAO 6 m telescope. The resolved structure consists of a compact core and an extended northern and south-eastern component. The compact core is resolved at all position angles and has a north-western, tail-shaped extension as well as a fainter, south-eastern extension. The K'-band FWHM diameter of this compact core is approximately 18 $\times$ 39 mas or 1.3 $\times$ 2.8 pc (FWHM of a single-component Gaussian fit; fit range 30-80% of the telescope cut-off frequency; the diameter errors are $\pm$ 4 mas), and the position angle (PA) of the north-western extension is -16 $\pm$ 4°. If 40% of the flux from the compact K' core is emission from a point source and 60% from a Gaussian intensity distribution, then a slightly larger FWHM of approximately 26 $\times$ 58 mas is obtained for the compact K' component. In the H band, the FWHM diameter of the compact core is approximately 18 $\times$ 45 mas ( $\pm$ 4 mas), and the PA is -18 $\pm$ 4°. The extended northern component (PA ~ 0°) has an elongated structure with a length of about 400 mas or 29 pc. The extended south-eastern component is fainter than the northern component. The K'- and H-band fluxes from the resolved compact core were measured to be 350 $\pm$ 90 mJy (i.e., K' ~ 8.2 $^{\rm m}$ ) and 70 $\pm$ 20 mJy ( H ~ 10.4 $^{\rm m}$ ), respectively. The PA of -16 $\pm$ 4° of the compact 18 $\times$ 39 mas core is very similar to that of the western wall (PA ~ -15°) of the bright region of the ionization cone. This suggests that the H- and K'-band emission from the compact core is both thermal emission and scattered light from dust near the western wall of a low-density, conical cavity or from the innermost region of a parsec-scale dusty torus that is heated by the central source (the dust sublimation radius of NGC 1068 is approximately 0.1-1 pc). The northern extended 400 mas structure lies near the western wall of the ionization cone and coincides with the inner radio jet (PA ~ 11°). The large distance from the core suggests that the K'-band emission of the northern extended component is scattered light from the western cavity region and the radio jet region.

Key words: techniques: interferometric -- galaxies: fundamental parameters -- galaxies: nuclei -- galaxies: photometry -- galaxies: Seyfert -- galaxies: individual: NGC 1068

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