2007ApJ...671L..37S

The first map of interstellar acetylene (C₂H₂) has been obtained with the Infrared Spectrograph on board the Spitzer Space Telescope. A spectral line map of the ν₅vibration-rotation band at 13.7 µm, carried out toward the star-forming region Cepheus A East, shows that the C₂H₂ emission peaks in a few localized clumps where gas-phase CO₂emission was previously detected with Spitzer. The distribution of excitation temperatures, derived from fits to the C₂H₂ line profiles, ranges from 50 to 200 K, which is consistent with that derived for gaseous CO₂–suggesting that both molecules probe the same warm gas component. The C₂H₂molecules are excited via radiative pumping by 13.7 µm continuum photons emanating from the HW2 protostellar region. We derive column densities ranging from a fewx10¹³ to ∼ 7x10¹⁴/cm2, corresponding to C₂H₂abundances of 1x10^–9 to 4x10^–8 with respect to H₂. The spatial distribution of the C₂H₂ emission and a roughly constant N(C₂H₂)/N(CO₂) strongly suggest an association with shock activity, most likely the result of the sputtering of acetylene in icy grain mantles.