2000A&A...356.1031C

We present the results of a study of the submillimetre wavelength continuum emission, at 450 and 850µm, 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 ∼70arcmin² (∼1.2pc²). 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 M_☉ 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 0.5M_☉ identified by Motte et al. (1998A&A...336..150M) in dust maps of the ρ 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.