Near-IR images of the torus and micro-spiral structure in NGC 1068 using adaptive optics ?
/ Authors
/ 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 Pueoat CFHT. The achieved resolution (0: 12) re- veals several components, particularly prominent on the (J K) image: a) an unresolved, conspicuous core (size < 9 pc); b) an elongated structure at P.A. 102, beginning to show up at ra- dius 15 pc; c) a S-shaped structure with radial extent 20 pc, including a bar-like central elongation at P.A. 15 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: 00 2 diameter core, (J-K)=7.0, (H-K)=3.8, lead to an intrinsic extinction AV 25, assuming classical dust grains at 1500 K. The elongated structure at P.A. 102 may trace the pres- ence of cooler dust within and around the torus. This interpre- tation is supported by two facts at least: a) the elongated struc- ture is perpendicular to the local radio jet originating at S1; b) its direction follows exactly that of the disk of ionized gas re- cently found with the VLBA. Regarding the S-shaped feature, the near-IR flux of the bar-like central elongation at P.A.= 4 , if interpreted in terms of free-free emission from ionized gas, is roughly consistent with the level of 5 GHz emission. How- ever, the radio spectrum behaviour is indicative of synchrotron emission and we rather interpret the 2.2 m emission as orig- inating 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 exponen-
Journal: Astronomy and Astrophysics