EDP Sciences
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Volume 431, Number 1, February III 2005
Page(s) 149 - 163
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361:200400057

A&A 431, 149-163 (2005)
DOI: 10.1051/0004-6361:200400057

Clumpy filaments of the Chamaeleon I cloud: C $\mathsf{^{18}}$O mapping with the SEST

L. K. Haikala1, 2, J. Harju2, K. Mattila2 and M. Toriseva2

1  Swedish-ESO Submillimetre Telescope, European Southern Observatory, Casilla 19001, Santiago, Chile
    e-mail: haikala@astro.helsinki.fi
2  Observatory, PO Box 14, 00014 University of Helsinki, Finland

(Received 16 June 2003 / Accepted 23 July 2004 )

The Chamaeleon I dark cloud (Cha I) has been mapped in ${{\rm C^{18}O}~(J=1{-}0)}$ with an angular resolution of $1\arcmin$ using the SEST telescope. The large scale structures previously observed with lower spatial resolution in the cloud turn into a network of clumpy filaments. The automatic Clumpfind routine developed by Williams et al. (1994) is used to identify individual clumps in a consistent way. Altogether 71 clumps were found and the total mass of these clumps is 230  $\ensuremath{{M}_\odot} $. The dense "cores" detected with the NANTEN telescope (Mizuno et al. 1999) and the very cold cores detected in the ISOPHOT serendipity survey (Tóth et al. 2000) form parts of these filaments but decompose into numerous "clumps". The filaments are preferentially oriented at right angles to the large-scale magnetic field in the region. We discuss the cloud structure, the physical characteristics of the clumps and the distribution of young stars. The observed clump mass spectrum is compared with the predictions of the turbulent fragmentation model of Padoan & Nordlund (2002). Agreement is found if fragmentation has been driven by very large-scale hypersonic turbulence, and if by now it has had time to dissipate into modestly supersonic turbulence in the interclump gas. According to numerical simulations, large-scale turbulence should have resulted in filamentary structures as seen in Cha I. The well-oriented magnetic field does not, however, support this picture, but suggests magnetically steered large-scale collapse. The origin of filaments and clumps in Cha I is thus controversial. A possible solution is that the characterization of the driving turbulence fails and that in fact different processes have been effective on small and large scales in this cloud.

Key words: ISM: clouds -- ISM: molecules -- ISM: structure -- ISM: individual objects: Chamaeleon I

SIMBAD Objects

© ESO 2005