2018ApJ...864..102M

The central region of the massive star-forming cloud G33.92+0.11 was investigated with the emission from the deuterated species HDCS and DCN observed at sub-arcsecond angular resolution (∼0.''7) using ALMA. HDCS shows a distributed emission throughout the region, and its large relative abundance in the most recent star-forming region suggests that there still exists a significant amount of cold gas associated with the hot core region. A high degree of HDCS fractionation (HDCS/H₂CS > 0.1) was found in the north region between star-forming clumps where the cold dense pre-collapse gas may still exist. DCN appears to have a good correlation with the continuum emission. This species traces both cold and warm dense gas probably by typical cold deuterium fractionation reactions and also by the lukewarm fractionation reactions. Near the densest cores where massive stars have already formed and dust mantles are evaporating, the DCN/HDCS abundance ratio was found to be larger by a factor of a few than other positions. This may suggest that the DCN abundance has been increased through the lukewarm fractionation processes in the gas phase.