DENSE CORES IN DARK CLOUDS .8. VELOCITY-GRADIENTS

We present an analysis of motions consistent with uniform rotation in dense cores (density greater than or similar to 10(4) cm-3; size approximately 0.1 pc). Twenty-nine of the 43 cores studied have a statistically significant gradient. The detected gradients range in magnitude from 0.3 to 4 km s-1 pc-1, corresponding to 2 x 10(-3) < beta < 1.4, with typical values beta approximately 0.02, where beta is the ratio of rotational to gravitational energy. Some gradients are spatially continuous and are consistent with uniform rotation, but other apparent gradients are caused by clump-clump motion, or sharp localized gradients, within a map. The motions in L1495, B217, L1251, L43, B361, and L1551 are discussed in detail. In L1551, the residuals of the fit to the NH3 velocity field indicate an outflow from IRS 5 in the same direction as the CO outflow. Gradient ofientation appears to be preserved over a range of density, as evidenced by comparing results for NH3 to fits of (CO)-O-18 and CS maps. There appears to be no correlation between the inferred rotation axis and the orientation of elongated cores, a result consistent with the relatively small energy of rotation in these regions. The magnitude of the velocity gradient in a core has no relation to the absence or presence of an associated young stellar object. We find that the specific angular momentum, J/M, scales roughly as R3/2, where R represents the diameter of the FWHM intensity contour in a map. This relationship between specific angular momentum and cloud size can be understood if (a) cores are in approximate virial equilibrium, (b) line width scales as cloud size roughly according to DELTAnu is-proportional-to R1/2, and (c) beta is roughly constant (i.e., independent of R) over the range of scales studied.