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تسجيل مستخدم جديدA multi-wavelength observation and investigation of six infrared dark clouds
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Context. Infrared dark clouds (IRDCs) are ubiquitous in the Milky Way, yet they play a crucial role in breeding newly-formed stars. Aims. With the aim of further understanding the dynamics, chemistry, and evolution of IRDCs, we carried out multi-wavelength observations on a small sample. Methods. We performed new observations with the IRAM 30 m and CSO 10.4 m telescopes, with tracers ${rm HCO^+}$, HCN, ${rm N_2H^+}$, ${rm C^{18}O}$, DCO$^+$, SiO, and DCN toward six IRDCs G031.97+00.07, G033.69-00.01, G034.43+00.24, G035.39-00.33, G038.95-00.47, and G053.11+00.05. Results. We investigated 44 cores including 37 cores reported in previous work and seven newly-identified cores. Toward the dense cores, we detected 6 DCO$^+$, and 5 DCN lines. Using pixel-by-pixel spectral energy distribution (SED) fits of the $textit{Herschel}$ 70 to 500 $mu$m, we obtained dust temperature and column density distributions of the IRDCs. We found that ${rm N_2H^+}$ emission has a strong correlation with the dust temperature and column density distributions, while ${rm C^{18}O}$ showed the weakest correlation. It is suggested that ${rm N_2H^+}$ is indeed a good tracer in very dense conditions, but ${rm C^{18}O}$ is an unreliable one, as it has a relatively low critical density and is vulnerable to freezing-out onto the surface of cold dust grains. The dynamics within IRDCs are active, with infall, outflow, and collapse; the spectra are abundant especially in deuterium species. Conclusions. We observe many blueshifted and redshifted profiles, respectively, with ${rm HCO^+}$ and ${rm C^{18}O}$ toward the same core. This case can be well explained by model envelope expansion with core collapse (EECC).
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