EDP Sciences
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Volume 389, Number 2, July II 2002
Page(s) 577 - 588
Section Diffuse matter in space
DOI http://dx.doi.org/10.1051/0004-6361:20020452

A&A 389, 577-588 (2002)
DOI: 10.1051/0004-6361:20020452

The threaded molecular clumps of Chamaeleon III

G. F. Gahm1, K. Lehtinen2, P. Carlqvist3, J. Harju2, M. Juvela2 and K. Mattila2

1  SCFAB, Stockholm Observatory, 106 91 Stockholm, Sweden
2  Observatory, PO Box 14, 00014 University of Helsinki, Finland
3  Alfvén Laboratory, Royal Institute of Technology, 100 44 Stockholm, Sweden

(Received 16 October 2001 / Accepted 22 March 2002 )

We have mapped large areas in the $\ion{Chamaeleon}{III}$ complex of molecular clouds with the SEST in 13CO( J=1-0) and in C 18O( J=1-0). The stronger CO emission coincides with areas of cold dust emission, which is distributed in long, but thin, wavy filaments. We identify some 40 clumps of enhanced CO emission in these filaments. In the southern part of $\ion{Cha}{III}$ the clumps are equidistant along the main zig-zag shaped filament. Here we find two systems of filaments moving at different radial velocities. At least part of the zig-zag patterns visible on optical images may be caused by overlapping filaments. All clumps are small (typically 0.02-0.05 pc in radius), and of small mass (typically 0.1-0.7  $M_{\odot}$, when assuming the "standard" C 18O/H 2 column density ratio). Also the average number densities are small, $n({\rm H_2}) =
1\times 10^4 {-} 8\times 10^4$ cm -3, and the density contrast between clump and interclump gas is only ~10. In addition the values of $\vert E_{\rm pot}\vert/E_{\rm kin}$ are unusually small, 0.03-0.33. These clumps have smaller masses than those so far identified in other molecular clouds. Previously reported clumps of larger masses in $\ion{Cha}{III}$ turn out to be composed of assemblies of clumps. There are no signs of star formation in $\ion{Cha}{III}$ (unlike $\ion{Cha}{I}$ and $\ion{Cha}{II}$), and our results indicate also that such activity is not expected. However, with the velocity dispersion of 0.2 km s -1 the clumps would leave the thin filaments on short timescales, and if the clumps as such are not confined by some external force, they would also lose their identity on even shorter timescales. We discuss the possibility that the clumps are confined by electromagnetic forces, and show that this may work with reasonable assumptions on the required magnetic field strength. We also discuss the possibility that the clumps are attached to magnetic ropes along the filamentary axis, in which case the clumps could swing back and forth perpendicularly to the axis, like they were threaded on elastic strings.

Key words: ISM: clouds -- ISM: structure

Offprint request: G. F. Gahm, gahm@astro.su.se

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