2009ApJ...705L..95I

We have performed C¹⁸O (J = 1-0) mapping observations of a 20'x20' area of the OMC-1 region in the Orion A cloud. We identified 65 C¹⁸O cores, which have a mean radius, a velocity width in FWHM, and an LTE mass of 0.18 ±0.03 pc, 0.40±0.15 km/s, and 7.2±4.5 M_☉, respectively. All the cores are most likely to be gravitationally bound by considering the uncertainty in the C¹⁸O abundance. We derived a C¹⁸O core mass function, which shows a power-law-like behavior above 5 M_☉. The best-fit power-law index of -2.3±0.3 is consistent with those of the dense core mass functions and the stellar initial mass function (IMF) previously derived in the OMC-1 region. This agreement strongly suggests that the power-law form of the IMF has been already determined at the density of ∼10³/cm3, traced by the C¹⁸O (J = 1-0) line. Consequently, we propose that the origin of the IMF should be searched in tenuous cloud structures with densities of less than 10³/cm3.