The TMRT K band observations towards 26 infrared dark clouds: NH3, CCS, and HC3N

We present one of the first Shanghai Tian Ma Radio Telescope (TMRT) K Band observations towards a sample 26 infrared dark clouds (IRDCs). observed (1,1), (2,2), (3,3), and (4,4) transitions NH$_{3}$ together with CCS (2$_{1}$-1$_{0}$) HC$_{3}$N $J\,$=2-1, simultaneously. The survey dramatically increases existing CCS-detected IRDC from 8 to 23, enabling better statistical study ratios carbon-chain molecules (CCM) N-bearing in IRDCs. With newly developed hyperfine group ratio (HFGR) method fitting inversion lines, we found gas temperature be between 10 18 K. column density for most IRDCs are less than 10$^{-2}$, distinguishing low-mass star-forming regions. carried out chemical evolution simulations based on three-phase model NAUTILUS. Our measurements CCM consistent evolutionary ages $\lesssim$10$^{5}$ yr models. Comparisons data models suggest that CCS, HC$_{3}$N, sensitive stages sources.