2006ApJ...650L..71S

We report the first detection of gas-phase CO₂emission in the star-forming region Cepheus A East, obtained by spectral line mapping of the ν₂bending mode at 14.98 µm with the Infrared Spectrograph on board the Spitzer Space Telescope. The gaseous CO₂emission covers a region about 35''x25'' in extent and results from radiative pumping by 15 µm continuum photons emanating predominantly from the HW2 protostellar region. The gaseous CO₂ exhibits a temperature distribution ranging from 50 to 200 K. A correlation between the gas-phase CO₂distribution and that of H₂S(2), a tracer of shock activity, indicates that the CO₂molecules originate in a cool postshock gas component associated with the outflow powered by HW2. The presence of CO₂ice absorption features at 15.20 µm toward this region and the lack of correlation between the IR continuum emission and the CO₂gas emission distribution further suggest that the gaseous CO₂molecules are mainly sputtered off grain mantles (by the passage of slow nondissociative shocks with velocities of 15-30 km/s) rather than sublimated through grain heating.