2015ApJ...803...70S

We have observed the clump G34.43+00.24 MM3 associated with an infrared dark cloud in DNC J = 3-2, HN¹³C J = 3-2, and N₂H⁺ J = 3-2 with the Atacama Large Millimeter/submillimeter Array (ALMA). The N₂H⁺ emission is found to be relatively weak near the hot core and the outflows, and its distribution is clearly anti-correlated with the CS emission. This result indicates that a young outflow is interacting with cold ambient gas. The HN¹³C emission is compact and mostly emanates from the hot core, whereas the DNC emission is extended around the hot core. Thus, the DNC and HN¹³C emission traces warm regions near the protostar differently. The DNC emission is stronger than the HN¹³C emission toward most parts of this clump. The DNC/HNC abundance ratio averaged within a 15"x15" area around the phase center is higher than 0.06. This ratio is much higher than the value obtained by the previous single-dish observations of DNC and HN¹³C J = 1-0 (∼0.003). It seems likely that the DNC and HNC emission observed with the single-dish telescope traces lower density envelopes, while that observed with ALMA traces higher density and highly deuterated regions. We have compared the observational results with chemical-model results in order to investigate the behavior of DNC and HNC in the dense cores. Taking these results into account, we suggest that the low DNC/HNC ratio in the high-mass sources obtained by the single-dish observations are at least partly due to the low filling factor of the high density regions.