Massive Quiescent Cores in Orion. II. Core Mass Function

We have surveyed submillimeter continuum emission from relatively quiescent regions in the Orion molecular cloud to determine how the core mass function in a high-mass star-forming region compares to the stellar initial mass function. Such studies are important for understanding the evolution of cores to stars, and for comparison to formation processes in high- and low-mass star-forming regions. We used the SHARC II camera on the Caltech Submillimeter Observatory telescope to obtain 350 μm data having angular resolution of about 9", which corresponds to 0.02 pc at the distance of Orion. Further data processing using a deconvolution routine enhances the resolution to about 3". Such high angular resolution allows a rare look into individually resolved dense structures in a massive star-forming region. Our analysis combining dust continuum and spectral line data defines a sample of 51 Orion molecular cores with masses ranging from 0.1 to 46 M_solar and a mean mass of 9.8 M_solar, which is 1 order of magnitude higher than the value found in typical low-mass star-forming regions, such as Taurus. The majority of these cores cannot be supported by thermal pressure or turbulence, and are probably supercritical. They are thus likely precursors of protostars. The core mass function for the Orion quiescent cores can be fitted by a power law with an index equal to -0.85+/-0.21. This is significantly flatter than the Salpeter initial mass function and is also flatter than the core mass function found in low and intermediate star-forming regions. When compared with other massive star-forming regions such as NGC 7538, this slope is flatter than the index derived for samples of cores with masses up to thousands of M_solar. Closer inspection, however, indicates slopes in those regions similar to our result if only cores in a similar mass range are considered. Based on the comparison between the mass function of the Orion quiescent cores and those of cores in other regions, we find that the core mass function is flatter in an environment affected by ongoing high-mass star formation. Thus, it is likely that environmental processes play a role in shaping the stellar IMF later in the evolution of dense cores and the formation of stars in such regions.