LABOCA mapping of the infrared dark cloud MSXDC?G304.74+01.32

摘要

Context. Infrared dark clouds (IRDCs) likelyrepresent very early stages of high-mass star/star cluster formation. Aims. The aim is to determine the physicalproperties and spatial distribution of dense clumps in the IRDC MSXDCG304.74+01.32 (G304.74), and bring these characteristics into relationto theories concerning the origin of IRDCs and their fragmentation intoclumps and star-forming cores. Methods. G304.74 was mapped in the 870m dustcontinuum with the LABOCA bolometer on APEX. The 870m map wascompared with the 1.2mm continuum map of the cloud by Béltranetal. (2006, A&A, 447, 221). ArchivalMSXand IRASinfrared data were used to study thenature and properties of the submillimetre clumps within the cloud. TheH2 column densities were estimated using boththe 870mdust emission and the MSX8m extinction data. The obtained values werecompared with near-infrared extinction which could be estimated along afew lines of sight. We compared the clump masses and their spatialdistribution in G304.74 with those in several other recently studiedIRDCs. Results. Twelve clumps were identified from the870mdust continuum map. Three of them are associated with theMSXand IRASpoint sources. Moreover, one of theclumps (SMM6) is associated with two MSX8m point-likesources. Thus, there are8clumps within G304.74which are not associated with mid-infrared (MIR) emission. The H2column densities derived from the dust continuum and extinction dataare similar. The comparison suggests that the dust temperature may beelevated (20-30 K) near the southern end of the cloud, whereas thestarless clumps in the centre and in the north are cool (K). There is a highlikelihood that the clump mass distributions in G304.74 and in severalother IRDCs represent the samples of the same parent distribution. Inmost cases the spatial distributions of clumps in IRDCs do not deviatesignificantly from random distributions. Conclusions. G304.74 contains several massive clumpsthat are not associated with MIRemission. On statisticalgrounds it is likely that some of them are or harbour high-massstarless cores (HMSCs). The fact that the clump mass distributions(resembling the high-mass stellar IMF), and in some cases also therandom-like spatial distributions, seem to be comparable betweendifferent IRDCs, is consistent with the idea that the origin of IRDCs,and their further sub-fragmentation down to scales of clumps is causedby supersonic turbulence in accordance with results from giantmolecular clouds. Key words: stars: formation - ISM: clouds- ISM: structure - radio continuum: ISM - submillimeter: ISM