The Chemical Structure of Young High-mass Star-forming Clumps. I. Deuteration

Abstract

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 N 2 H + , HCN, HNC, and HCO + isotopologues are subthermally excited; and (2) the deuteration of N 2 H + is more efficient than that of 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 ( T kin ∼ 14 K, N (NH 3 ) ∼ 9 × 10 15 cm −2 ). In contrast, single deuteration of NH 3 is insensitive to the environmental difference between P1 and S; and (3) single deuteration of CH 3 OH (>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.