Deuteration in infrared dark clouds

Abstract

Much of the dense gas in molecular clouds has a filamentary structure but the detailed structure and evolution of this gas is poorly known. We have observed 54 cores in infrared dark clouds (IRDCs) using N${}_2$H${}^{+}$ (1-0) and (3-2) to determine the kinematics of the densest material, where stars will form. We also observed N${}_2$D${}^{+}$ (3-2) towards 29 of the brightest peaks to analyse the level of deuteration which is an excellent probe of the quiescent of the early stages of star formation. There were 13 detections of N${}_2$D${}^{+}$ (3-2). This is one of the largest samples of IRDCs yet observed in these species. The deuteration ratio in these sources ranges between 0.003 and 0.14. For most of the sources the material traced by N${}_2$D${}^{+}$ and N${}_2$H${}^{+}$ (3-2) still has significant turbulent motions, however three objects show subthermal N${}_2$D${}^{+}$ velocity dispersion. Surprisingly the presence or absence of an embedded 70 $\mu$m source shows no correlation with the detection of N${}_2$D${}^{+}$ (3-2), nor does it correlate with any change in velocity dispersion or excitation temperature. Comparison with recent models of deuteration suggest evolutionary time-scales of these regions of several free-fall times or less.

15 pages, 12 figures

References in corpus (5)

• Trigonometric Parallaxes of Massive Star Forming Regions: VI. Galactic Structure, Fundamental Parameters and Non-Circular Motions
• An Ammonia Spectral Atlas of Dense Cores in Perseus
• The N2D+/N2H+ ratio as an evolutionary tracer of Class 0 protostars
• The Deuterium Fractionation Timescale in Dense Cloud Cores: A Parameter Space Exploration
• A MALT90 study of the chemical properties of massive clumps and filaments of infrared dark clouds

Cited by in corpus (5)

• Investigating the structure and fragmentation of a highly filamentary IRDC
• Chemistry of the High-Mass Protostellar Molecular Clump IRAS 16562-3959
• Deuterium fractionation and H2D+ evolution in turbulent and magnetized cloud cores
• Physical and chemical modeling of the starless core L1512
• Fast deuterium fractionation in magnetized and turbulent filaments