Mid-J CO Shock Tracing Observations of Infrared Dark Clouds I

Abstract

Infrared dark clouds (IRDCs) are dense, molecular structures in the interstellar medium that can harbour sites of high-mass star formation. IRDCs contain supersonic turbulence, which is expected to generate shocks that locally heat pockets of gas within the clouds. We present observations of the CO J = 8-7, 9-8, and 10-9 transitions, taken with the Herschel Space Observatory, towards four dense, starless clumps within IRDCs (C1 in G028.37+00.07, F1 and F2 in G034.43+0007, and G2 in G034.77-0.55). We detect the CO J = 8-7 and 9-8 transitions towards three of the clumps (C1, F1, and F2) at intensity levels greater than expected from photodissociation region (PDR) models. The average ratio of the 8-7 to 9-8 lines is also found to be between 1.6 and 2.6 in the three clumps with detections, significantly smaller than expected from PDR models. These low line ratios and large line intensities strongly suggest that the C1, F1, and F2 clumps contain a hot gas component not accounted for by standard PDR models. Such a hot gas component could be generated by turbulence dissipating in low velocity shocks.

14 pages, 8 figures, 5 tables, accepted by A&A, minor updates to match the final published version

References in corpus (5)

• Theory of Star Formation
• Deuteration and evolution in the massive star formation process: the role of surface chemistry
• Molecular Outflows and a Mid-Infrared Census of the Massive Star-Formation Region Associated with IRAS 18507+0121
• Distributed Low-Mass Star Formation in the IRDC G34.43+00.24
• Mid-J CO observations of Perseus B1-East 5: evidence for turbulent dissipation via low-velocity shocks

Cited by in corpus (6)

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• Investigating the structure and fragmentation of a highly filamentary IRDC
• A multi-wavelength observation and investigation of six infrared dark clouds
• Similar complex kinematics within two massive, filamentary infrared dark clouds
• Multicomponent kinematics in a massive filamentary IRDC
• Mid-J CO Shock Tracing Observations of Infrared Dark Clouds III: SLED fitting