Clumpy filaments of the Chamaeleon I cloud: C18O mapping with the SEST

Abstract

The Chamaeleon I dark cloud (Cha I) has been mapped in C18O (J = 1-0) with an angular resolution of 1′ 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 M⊙. 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.