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Paper: Small-Scale Structure of Low-Density Molecular Gas Revealed by Extensive High-Resolution Imaging in 12CO
Volume: 217, Imaging at Radio Through Submillimeter Wavelengths
Page: 92
Authors: Sakamoto, S.
Abstract: High-resolution observations of low-density regions of molecular clouds will provide the key to the detailed spatial and kinematical structure of molecular clouds in their early stages of evolution. It is because the timescales of dynamical and chemical evolution are slow in these regions and also because they are mostly free from the effects of star formation. We made extensive (~ 1circ) and sensitive observations of low-density molecular gas in three high-latitude clouds (MBM 32, MBM 54, and MBM 55) and in the envelope of L1641 in 12CO J = 1--0 emission with the 15'' (0.007 pc at 100 pc) beam of the Nobeyama 45m telescope. We found that the size of the smallest structure of low-density molecular gas traced by 12CO J = 1--0 emission is ~0.03 pc and probably less. In addition, we discovered in these high-latitude clouds a number of compact steep-velocity-gradient features which are subparsec-scale outflow-like velocity structures probably not powered by young stellar objects. They have a typical size of ~0.05 pc and a typical velocity gradient of ~40 km/s -1pc -1, and thus may be transient with their typical dynamical timescale of ~ 2 × 104yr. They lack YSO candidates or H2 v = 1--0 S(1) emission features in their vicinity. They are most likely weak shocks excited by collisions of clumps.
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