A Census of Dust Absorption at the Galactic Centre

The Galactic Centre offers a uniquely valuable line of sight for studies of the nature of dust in the ISM, but the long-held assumption that the line of sight samples only the diffuse ISM has been subverted by ground-based and ISO observations demonstrating the presence of absorption bands due to solid-phase volatile ices in the field. Spatial variability of the observed features suggests a patchy distribution of even the foreground diffuse-medium absorption. To map this clumpy distribution and to produce an inventory of the dust components, we are carrying out a narrow-band imaging survey over a field which extends from the Galactic Centre to beyond the circumnuclear ring, using both IRCAM3 and Michelle on UKIRT to cover the 3 μm water ice, 3.3 μm PAH, 3.4 μm hydrocarbon and 9.7 μm silicate absorption features. This paper presents the rationale for this programme and reports on progress with analysis of the survey data.