2009ApJ...691.1560I

We have carried out an H¹³CO⁺(J = 1 - 0) core survey in a large area of 1 deg², covering most of the dense region in the Orion B molecular cloud, using the Nobeyama 45 m radio telescope with the 25-BEam Array Receiver System. We cataloged 151 dense cores using the clumpfind method. The cores have mean radius, velocity width, and mass of 0.10±0.02 pc, 0.53±0.15 km/s, and 8.1±6.4 M_☉, respectively, which are very similar to those in the Orion A cloud. We examined the spatial relation between our H¹³CO⁺ cores and the 850 µm cores observed by Johnstone and colleagues in 2001 and 2006, and found that there are two types of spatial relationships: H¹³CO⁺ cores with and without the 850 µm cores. Since the mean density of the 850 µm cores is higher than that of the H¹³CO⁺ cores, we can interpret the H¹³CO⁺ cores with 850 µm cores as being more centrally concentrated and hence more evolved, compared with those without. Considering the relationship between the masses of the H¹³CO⁺ and 850 µm cores, we estimate the 850 µm core mass function (CMF) using the H¹³CO⁺ CMF through the generalization of the confusion model proposed by Ikeda and colleagues in 2007. Our predicted 850 µm CMF is found to be quite consistent with that directly derived by Johnstone and colleagues. Furthermore, we predict the initial mass function (IMF) by the generalized confusion model assuming a star formation efficiency of 40% for the H¹³CO⁺ cores, and found that our predicted IMF is consistent with the Galactic field-averaged IMF within uncertainties. This agreement may indicate that the origin of the IMF goes back to the cloud structures with densities of less than 10⁴/cm3.