MOLECULAR CLOUD CORES IN THE ORION A CLOUD .1. NOBEYAMA CS (1-0) SURVEY

A first high-resolution survey of molecular cloud cores in the Orion A giant molecular cloud is reported. We identified 125 molecular cloud cores from an analysis of the spatial and velocity distribution of the CS (1-0) emission. The cores are generally elongated along the filamentary molecular cloud, and the axial ratio is about 0.5. The mass spectrum index of the cores is - 1.6 for M greater-than-or-equal-to 50 M.. The physical properties of the cores identified in Orion are compared with those of cores in dark clouds reported in the literature. The average radius of the cores in the Orion A cloud, 0.16 pc, is comparable to that of the cores in dark clouds. In contrast, the Orion A cloud contains molecular cloud cores with large line widths (1-2 km s-1 FWHM) and large masses (M > 100 M.), which are rarely observed in dark clouds. We suggest that the line width-radius relation differs between these two samples. Within the Orion A cloud the CS line width, core mass, average density, and core-to-core velocity dispersion all decrease toward the south. These trends can be seen, even when the cores with young stellar objects are excluded from the sample. We discuss the implications of the line width-radius relation, and suggest that cores in giant molecular clouds are bounded by higher external pressure, which eventually leads to massive star formation