A method for mapping the aliphatic hydrocarbon content of interstellar
  dust towards the Galactic Centre
  In the interstellar medium, the cosmic elemental carbon abundance includes
the total carbon in both gas and solid phases. The aim of the study was to
trial a new method for measuring the amount and distribution of aliphatic
carbon within interstellar dust over wide fields of view of our Galaxy. This
method is based on measurement of the 3.4 $\mu$m absorption feature from
aliphatic carbonaceous matter. This can readily be achieved for single sources
using IR spectrometers. However, making such measurements over wide fields
requires an imaging IR camera, equipped with narrow-band filters that are able
to sample the spectrum. While this cannot produce as good a determination of
the spectra, the technique can be applied to potentially tens to hundreds of
sources simultaneously, over the field of view of the camera. We examined this
method for a field in the centre of the Galaxy, and produced a map showing the
variation of 3.4 $\mu$m optical depth across it.
