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R. Mason (NOAO), G. Wright (UK Astronomy Technology Centre), A. Adamson (Joint Astronomy Centre), Y. Pendleton (NASA-Ames)
We have modelled new and existing infrared spectroscopic and polarimetric observations of NGC1068 to investigate the size and structure of the grains in this archetypal dusty AGN. The best fit to the H, K and L band polarization of this object is achieved if the polarizing grains are somewhat larger than those seen in the Galactic diffuse ISM. Contrary to the predictions of the models of coated silicate grains that we present here, the 3.4\mum aliphatic hydrocarbon dust absorption band is unpolarized. This suggests that the aligned grains in NGC1068 do not take the form of silicate cores with organic mantles, and therefore do not arise from energetic processing of ice-coated molcular cloud-type grains. We also present a comparison of the 3.4\mum band in NGC1068 with that observed in the Galactic diffuse ISM and in a protoplanetary nebula. The striking similarity of the features in all cases underlines the need for spectroscopy of more galaxies at 3.4\mum and in the mid-IR, to better understand how dust formation and evolution are influenced by the properties of the environment in which the dust exists.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.