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

G. Weigelt, M. Wittkowski, Y.Y. Balega, T. Beckert, W.J. Duschl, K.-H. Hofmann, A.B. Men'shchikov, D. Schertl

A&A 425, pp. 77-87 (2004)


We present near-infrared bispectrum speckle interferometry studies of the nuclear region of the Seyfert 2 galaxy NGC1068. 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 6m 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 × 39 mas or 1.3 × 2.8 pc (FWHM of a single-component Gaussian fit; fit range 30–80% of the telescope cut-off frequency; the diameter errors are ±4mas), and the position angle (PA) of the north-western extension is –16 ± 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 × 58 mas is obtained for the compact K' component. In the H band, the FWHM diameter of the compact core is approximately 18 × 45 mas (±4mas), and the PA is –18 ± 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 ± 90 mJy (i.e., K' ∼ 8.2m) and 70 ± 20 mJy (H ∼ 10.4m), respectively. The PA of –16 ± 4° of the compact 18 × 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 NGC1068 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.

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