A C 18O Survey of Dense Cloud Cores in Taurus: Core Properties

This paper discusses observational results of physical properties of dense cores in the Taurus complex. The observations were carried out in the C¹⁸O (J = 1-0) line at a linear resolution of 0.1 pc with the 4 m millimeter radio telescope at Nagoya University. Based on the previous ¹³CO observations of Mizuno et al. (1995) as a guide map, we obtained 7200 spectra (8 deg²) at a 2' grid spacing, corresponding to more than 90% of the area whose molecular column density is greater than 3.5 x 10²¹ cm⁻². The total molecular mass of the C¹⁸O cloud is estimated to be 2900 Msun, which is 43% of the mass of the ¹³CO cloud. About 97% of the C¹⁸O spectra have an optical depth smaller than 0.5, and the C¹⁸O emission is optically thin over almost all the region at a size scale down to ∼0.1 pc. The basic structure of the C¹⁸O cloud is clumpy. We identified 40 dense cores of n(H₂) ∼10⁴ cm⁻³, whose mass ranges from 1 to 80 Msun. The average physical parameters of the C¹⁸0 cores are as follows: radius 0.23 pc, line width 0.49 km s⁻¹, column density 6.9 x 10²¹ cm⁻², and mass 23 Msun. The mass spectrum of the cores, dN/dM versus M, is fitted by a power law with an index of -09±02 which is significantly smaller than those of the previous surveys. Most of the cores are spatially elongated; the average aspect ratio is 1.8, and the direction of the major axis of the cores tends to be perpendicular to the typical direction of the optical polarization vectors. An analysis of correlations among the physical quantities of the cores indicates that the line width has a positive correlation with the mass and the column density but not with the size. Most of the cores are roughly gravitationally bound and at least approximately in virial equilibrium.