A multiwavelength observation and investigation of six infrared dark clouds⋆
1 National Astronomical Observatories, CAS, 20A Datun Road, Chaoyang District, 100012 Beijing, PR China
2 University Observatory Munich, Scheinerstrasse 1, 81679 Munich, Germany
3 Xinjiang Astronomical Observatory, CAS, 150, Science 1-street, 830011 Urumqi, PR China
4 NAOC-TU Joint Center for Astrophysics, 850000 Lhasa, PR China
Received: 22 September 2016
Accepted: 26 November 2016
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 multiwavelength observations on a small sample.
Methods. We performed new observations with the IRAM 30 m and CSO 10.4 m telescopes, with tracers HCO+, HCN, N2H+, C18O, 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 Herschel 70 to 500 μm, we obtained dust temperature and column density distributions of the IRDCs. We found that N2H+ emission has a strong correlation with the dust temperature and column density distributions, while C18O showed the weakest correlation. It is suggested that N2H+ is indeed a good tracer in very dense conditions, but C18O 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 HCO+ and C18O toward the same core. This case can be well explained by model “envelope expansion with core collapse (EECC)”.
Key words: infrared: stars / stars: formation / ISM: IRDCs / HII regions / radio lines: ISM
The final datacubes (HCO+, HCN, N2H+, C18O) are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (184.108.40.206) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/598/A76
© ESO, 2017