We present a detailed study of the Circinus Galaxy , investigating its star formation , dust and gas properties both in the inner and outer disk .
To achieve this , we obtained high-resolution Spitzer mid-infrared images with the IRAC ( 3.6 , 5.8 , 4.5 , 8.0 \mu m ) and MIPS ( 24 and 70 \mu m ) instruments and sensitive H i data from the Australia Telescope Compact Array ( ATCA ) and the 64-m Parkes telescope .
These were supplemented by CO maps from the Swedish-ESO Submillimetre Telescope ( SEST ) .
Because Circinus is hidden behind the Galactic Plane , we demonstrate the careful removal of foreground stars as well as large- and small-scale Galactic emission from the Spitzer images .
We derive a visual extinction of A _ { V } = 2.1 mag from the Spectral Energy Distribution of the Circinus Galaxy and total stellar and gas masses of 9.5 \times 10 ^ { 10 } M _ { \odot } and 9 \times 10 ^ { 9 } M _ { \odot } , respectively .
Using various wavelength calibrations , we find obscured global star formation rates between 3 and 8 M _ { \odot } yr ^ { -1 } .
Star forming regions in the inner spiral arms of Circinus , which are rich in H i , are beautifully unveiled in the Spitzer 8 \mu m image .
The latter is dominated by polycyclic aromatic hydrocarbon ( PAH ) emission from heated interstellar dust .
We find a good correlation between the 8 \mu m emission in the arms and regions of dense H i gas .
The ( PAH 8 \mu m ) / 24 \mu m surface brightness ratio shows significant variations across the disk of Circinus .