Observations of DNC and DCO + toward the ∫-shaped Filament and Starless Cores in the Orion Molecular Clouds

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Abstract Although the deuterium fraction is known to be a powerful evolutionary tracer, its variation within individual molecular cloud cores is still poorly understood. The northern ∫-shaped filament and 20 individual starless cores in the Orion A and B clouds were mapped in the deuterated molecules of DNC and DCO + with the receiver 7BEE installed on the Nobeyama 45 m radio telescope. In a ∼ 5 ′ × 30 ′ map of the northern ∫-shaped filament in the Orion A cloud, the DNC emission is detected over the filament, whereas the DCO + emission is localized toward OMC-3, the northernmost region of the filament. The difference in distribution between DNC and DCO + can be attributed to that between N- and C-bearing molecules as previously suggested by K. Tatematsu et al. (2008). High DNC/HN 13 C column density ratios were observed in OMC-2 and OMC-3, and low ratios in OMC-1. It seems that OMC-2 and OMC-3 still contain molecular gas close to the onset of star formation. In 3 ′ × 3 ′ maps of the individual starless cores in Orion, the column density ratios of DNC/HN 13 C and DCO + /H 13 CO + were found to be rather constant locally within each core, although the core-to-core variation is not small. Similar timescales of deuterization, depletion, and dynamical evolution might explain the locally constant ratio.

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