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Structure, star formation and magnetic fields in the OMC1 region
Received 1 September 1999 / Accepted 25 November 1999
We present the results of a study of the submillimetre wavelength continuum emission, at 450 and 850 , encompassing the OMC1 region in the northern part of the Orion A cloud, and focusing on the structure and star formation in an area of about 70 arcmin2 (1.2 pc2). Our observations are 3 times deeper in flux than previous submillimetre observations of this region and we have found a number of pre-stellar dust clumps in the region from which mass functions were determined. Our clump mass functions include objects down to 0.1 and the power-law slope of -1.5 is similar to that generally found from spectral line observations of molecular gas clumps. The data do not show the steeper slope of -2.5 for masses above 0.5 identified by Motte et al. (1998) in dust maps of the Ophiuchus low-mass star-forming region, possibly indicating different collapse processes. Polarimetry data for the north-east bar and KL regions of OMC1 were also obtained, and it is apparent that the field orientations with respect to cloud elongation differ between star-forming and non-star-forming regions. The main OMC1 ridge is consistent with collapse down field lines while the north-east bar has a field structure roughly outlining the HII region. The dominant physical processes apear to be pressure from the expanding HII region and fragmentation on the Jeans scale, rather than magnetic effects.
Key words: polarization stars: formation ISM: individual objects: OMC1 ISM: magnetic fields ISM: structure
Send offprint requests to: J.S. Greaves
Online publication: April 17, 2000