The Chemical Structure of Young High-mass Star-forming Clumps. II. Parsec-scale CO Depletion and Deuterium Fraction of HCO<sup>+</sup>
Siyi Feng, Di Li, P. Caselli, Fujun Du, Yuxin Lin, O. Sipilä, H. Beuther, Patricio Sanhueza, Ken’ichi Tatematsu, Sheng‐Yuan Liu, Qizhou Zhang, Y. Wang, Taylor Hogge, Izaskun Jiménez-Serra, Xing Lu, Tie Liu, Ke Wang, Zhi-Yu Zhang, Sarolta Zahorecz, Guang-Xing Li, Hauyu Baobab Liu, Jinghua Yuan
Abstract
Abstract The physical and chemical properties of cold and dense molecular clouds are key to understanding how stars form. Using the IRAM 30 m and NRO 45 m telescopes, we carried out a Multiwavelength line-Imaging survey of the 70 μ m-dArk and bright clOuds (MIAO). At a linear resolution of 0.1–0.5 pc, this work presents a detailed study of parsec-scale CO depletion and HCO + deuterium (D-) fractionation toward four sources (G11.38+0.81, G15.22–0.43, G14.49–0.13, and G34.74–0.12) included in our full sample. In each source with T < 20 K and n H ∼ 10 4 –10 5 cm −3 , we compared pairs of neighboring 70 μ m bright and dark clumps and found that (1) the H 2 column density and dust temperature of each source show strong spatial anticorrelation; (2) the spatial distribution of CO isotopologue lines and dense gas tracers, such as 1–0 lines of H 13 CO + and DCO + , are anticorrelated; (3) the abundance ratio between C 18 O and DCO + shows a strong correlation with the source temperature; (4) both the C 18 O depletion factor and D-fraction of HCO + show a robust decrease from younger clumps to more evolved clumps by a factor of more than 3; and (5) preliminary chemical modeling indicates that chemical ages of our sources are ∼8 × 10 4 yr, which is comparable to their free-fall timescales and smaller than their contraction timescales, indicating that our sources are likely dynamically and chemically young.