2001A&A...365L.353S

We report the detection of absorption features in the 6-8µm 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, we infer that the powerful central source responsible for the mid-infrared emission must be deeply enshrouded. Since this emission is warm and originates in a compact region, an AGN must be hiding in the nucleus of NGC 4418.