Abstract
We report the detection of absorption features in the 6–8 μm region superimposed on a featureless mid-infrared continuum in NGC 4418. For several of these features this is the first detection in an external galaxy. We compare the absorption spectrum of NGC 4418 to that of embedded massive protostars and the Galactic centre, and attribute the absorption features to ice grains and to hydrogenated amorphous carbon grains. From the depth of the ice features, the central source responsible for the mid-infrared emission must be deeply enshrouded. Combined with the small size of the mid-infrared source, only an AGN can be effectively hidden within the geometry at hand.
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Spoon, H., Keane, J., Tielens, X., Lutz, D., Moorwood, A. (2001). The Obscured Mid-Infrared Continuum of NGC 4418: A Dust- and Ice-Enshrouded AGN. In: Tacconi, L., Lutz, D. (eds) Starburst Galaxies: Near and Far. Springer Proceedings in Physics, vol 88. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-56538-0_17
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DOI: https://doi.org/10.1007/978-3-642-56538-0_17
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