We report spatially-resolved variations in the 3.4- \mu m hydrocarbon absorption feature and the 3.3- \mu m 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 _ { { 3.4 \mu } m } \sim 0.1 in the core which decreases to the west and increases to the east .
This is consistent with increased extinction out to \sim 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 \pm 4 arcsec , outside the differential extinction region .
The asymmetry in the 3.4- \mu m absorption band reflects that seen in the 9.7- \mu m 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 _ { { 3.4 \mu } m } / \tau _ { { 9.7 \mu } m } \sim 0.06 \pm 0.01 .
This indicates well-mixed hydrocarbon and silicate dust populations , with no evidence for significant changes near the nucleus .