摘要
We present one of the first Shanghai Tian Ma Radio Telescope (TMRT) K Band observations towards a sample of 26 infrared dark clouds (IRDCs).We observed the (1,1),(2,2),(3,3),and (4,4) transitions of NH_(3) together with CCS (2_(1)–>1_(0)) and HC_(3)NJ=2-1,simultaneously.The survey dramatically increases the existing CCS-detected IRDC sample from 8 to 23,enabling a better statistical study of the ratios of carbon-chain molecules (CCM) to N-bearing molecules in IRDCs.With the newly developed hyperfine group ratio (HFGR) method of fitting NH_(3) inversion lines,we found the gas temperature to be between 10 and18 K.The column density ratios of CCS to NH_(3) for most of the IRDCs are less than 10^(-2),distinguishing IRDCs from low-mass star-forming regions.We carried out chemical evolution simulations based on a three-phase chemical model NAUTILUS.Our measurements of the column density ratios between CCM and NH_(3) are consistent with chemical evolutionary ages of 10^(5) yr in the models.Comparisons of the data and chemical models suggest that CCS,HC_(3)N,and NH_(3) are sensitive to the chemical evolutionary stages of the sources.
基金
supported by the National Natural Science Foundation of China (Grant Nos. 11988101, 11725313, 11911530226, and 11403041)
the Chinese Academy of Sciences International Partnership Program (Grant No. 114A11KYSB20160008)
financial support from the State Agency for Research of the Spanish MCIU through the AYA2017-84390-C2-1-R grant (co-funded by FEDER)
through the “Center of Excellence Severo Ochoa” award for the Instituto de Astrofísica de Andalucia (Grant No. SEV-2017-0709)
Gary A. Fuller also acknowledges support from the Collaborative Research Centre 956, funded by the Deutsche Forschungsgemeinschaft (Grant No. 184018867)。
