The distribution of deuterated formaldehyde within Orion-KL

Abstract

We report the first high angular resolution imaging (3".4 × 3".0) of deuterated formaldehyde (HDCO) toward Orion-KL, carried out with the Submillimeter Array. We find that the spatial distribution of the formaldehyde emission systematically differs from that of methanol: while methanol is found toward the inner part of the region, HDCO is found in colder gas that wraps around the methanol emission on four sides. The HDCO/H_2CO ratios are determined to be 0.003–0.009 within the region, up to an order of magnitude higher than the D/H measured for methanol. These findings strengthen the previously suggested hypothesis that there are differences in the chemical pathways leading to HDCO (via deuterated gas-phase chemistry) and deuterated methanol (through conversion of formaldehyde into methanol on the surface of icy grain mantles).

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