CHEMISTRY IN INFRARED DARK CLOUD CLUMPS: A MOLECULAR LINE SURVEY AT 3 mm

By P. Sanhueza, J. Jackson, J. Foster, G. Garay, Andrea Silva, S. Finn. 2011

138 citations recorded by the source corpus.

We have observed 37 Infrared Dark Clouds (IRDCs), containing a total of 159 clumps, in high-density molecular tracers at 3 mm using the 22 m ATNF Mopra Telescope located in Australia. After determining kinematic distances, we eliminated clumps that are not located in IRDCs and clumps with a separation between them of less than one Mopra beam. Our final sample consists of 92 IRDC clumps. The most commonly detected molecular lines are (detection rates higher than 8%) N2H+, HNC, HN13C, HCO+, H13CO+, HCN, C2H, HC3N, HNCO, and SiO. We investigate the behavior of the different molecular tracers and look for chemical variations as a function of an evolutionary sequence based on Spitzer IRAC and MIPS emission. We find that the molecular tracers behave differently through the evolutionary sequence and some of them can be used to yield useful relative age information. The presence of HNC and N2H+ lines does not depend on the star formation activity. On the other hand, HC3N, HNCO, and SiO are predominantly detected in later stages of evolution. Optical depth calculations show that in IRDC clumps the N2H+ line is optically thin, the C2H line is moderately optically thick, and HNC and HCO+ are optically thick. The HCN hyperfine transitions are blended, and, in addition, show self-absorbed line profiles and extended wing emission. These factors combined prevent the use of HCN hyperfine transitions for the calculation of physical parameters. Total column densities of the different molecules, except C2H, increase with the evolutionary stage of the clumps. Molecular abundances increase with the evolutionary stage for N2H+ and HCO+. The N2H+/HCO+ and N2H+/HNC abundance ratios act as chemical clocks, increasing with the evolution of the clumps.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/4cd11bba95a62650df9e714cadc01ef69533fe48

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In Astronomy and Astrophysics

1. P. Myers
2. T. Pillai
3. R. Gutermuth
4. L. Testi
5. Th. Henning
6. T. Bourke
7. F. Wyrowski
8. H. Kirk

In Instrumentation

1. T. Pillai
2. P. Myers
3. Th. Henning
4. F. Wyrowski
5. R. Gutermuth
6. Qizhou Zhang
7. L. Testi
8. H. Kirk

Citations in the corpus

• Hierarchical fragmentation and differential star formation in the Galactic ‘Snake’: infrared dark cloud G11.11−0.12 (2014, methodology): “This is what led to the cloud complexes containing such regions tobe ⋆ E-mail: kwang@eso.org coined “infrared-dark clouds” (IRDCs; Perault et al. 1996;Egan et al. 1998; Hennebelle et al. 2001; Simon et al. 2006a,b; Peretto & Fuller 2009).”
• FILAMENTARY ACCRETION FLOWS IN THE EMBEDDED SERPENS SOUTH PROTOCLUSTER (2013, background): “All three of these molecular species are expected to be good tracers of dense gas (see, e.g., the discussion in Sanhueza et al 2012; Bergin & Tafalla 2007), which is confirmed by their good correspondence to the dust emission.”