Widespread acetaldehyde near the Galactic Centre

Abstract

We present Giant Meterwave Radio Telescope images of the 1065 MHz emission from the 1₁₁→1₁₀ rotational transition of acetaldehyde (CH₃CHO) in the molecular cloud complex Sgr B2. Our observations are unique in that they have a high spatial resolution (∼4''), while still being sensitive to large-scale emission. Most complex organic molecules in this cloud (e.g. acetone, methyl formate, acetic acid) are concentrated in a very small core, ∼0.1 pc across. In contrast, acetaldehyde is found to be spread over a region at least 100 times larger in extent. The line emission is confined to regions with radio continuum emission and correlates well (in both position and velocity) with formaldehyde absorption towards this continuum; this is consistent with earlier single dish results suggesting that it is likely to be weakly mased. Our observations also suggest that grain mantle destruction by shocks plays an important role in the observed gas phase abundance of CH₃CHO in Sgr B2.