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

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 × 39 mas or 1.3 × 2.8 pc (FWHM of a single-component Gaussian fit; fit range 30-80&%slash; of the telescope cut-off frequency; the diameter errors are ±4 mas), 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 (±4 mas), 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' ∼ 8.2^m) and 70 ± 20 mJy (H ∼ 10.4^m), 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 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.

Based on observations made with the 6 m BTA telescope, which is operated by the Special Astrophysical Observatory (SAO), Russia.