2019/08/31 by S. Feng, P. Caselli, K. Wang +3 · 1 citation
Physics and Astronomy · #astro-ph.GA #astro-ph.SR
paper · pdf · doi:10.3847/1538-4357/ab3a42
arxiv created 2019/08/31 · arxiv updated 2019/10/09
The chemical structure of high-mass star nurseries is important for a general understanding of star formation. Deuteration is a key chemical process in the earliest stages of star formation because its efficiency is sensitive to the environment. Using the IRAM-30 m telescope at 1.3--4.3 mm wavelengths, we have imaged two parsec-scale high-mass protostellar clumps (P1 and S) that show different evolutionary stages but are located in the same giant filamentary infrared dark cloud G28.34+0.06. Deep spectral images at subparsec resolution reveal the dust and gas physical structures of both clumps. We find that (1) the low-J lines of \rm N2H+, HCN, HNC, and \rm HCO+ isotopologues are subthermally excited; and (2) the deuteration of \rm N2H+ is more efficient than that of \rm HCO+, HCN, and HNC by an order of magnitude. The deuterations of these species are enriched toward the chemically younger clump S compared with P1, indicating that this process favors the colder and denser environment (\rm Tkin ∼14 K, \rm N(NH3) ∼ 9× 1015 cm-2). In contrast, single deuteration of \rm NH3 is insensitive to the environmental difference between P1 and S; and (3) single deuteration of \rm CH3OH (\rm > 10%) is detected toward the location where CO shows a depletion of ∼10. This comparative chemical study between P1 and S links the chemical variations to the environmental differences and shows chemical similarities between the early phases of high- and low-mass star-forming regions.