The Spatial Variation of the 3micron Dust Features in Circinus
  We report spatially-resolved variations in the 3.4micron hydrocarbon
absorption feature and the 3.3micron polycyclic aromatic hydrocarbon (PAH)
emission band in the Circinus galaxy over the central few arcsec. The
absorption is measured towards warm emitting dust associated with Coronal line
regions to the east and west of the nucleus. There is an absorption optical
depth tau(3.4um) ~0.1 in the core which decreases to the west and increases to
the east. This is consistent with increased extinction out to ~40 pc east of
the core, supported by the Coronal emission line intensities which are
significantly lower to the east than the west. PAH emission is measured to be
symmetrically distributed out to +/- 4 arcsec, outside the differential
extinction region. The asymmetry in the 3.4micron absorption band reflects that
seen in the 9.7micron silicate absorption band reported by Roche et al. (2006)
and the ratio of the two absorption depths remains approximately constant
across the central regions, with tau(3.4um) / tau(9.7um) ~ 0.06 +/-0.01. This
indicates well-mixed hydrocarbon and silicate dust populations, with no
evidence for significant changes near the nucleus.
