The Structure and Angular Momentum Content of Dark Clouds.

This thesis reports on a study of the structure, kinematics, and dynamics of eight dark clouds, with emphasis on the presence and influence of rotation. Rotation is confirmed in only three of six clouds previously reported to possess such motion, suggesting that rapid rotation in dark clouds is rarer than had been suspected. One cloud (CRL 437) contains a bipolar flow, while the rotation model is in jepordy for B163 and B163SW due to apparent gross asymmetries in their mass distributions. Cloud morphology is investigated by using high -quality ('13)CO and ('12)CO J = 1 (--->) 0 spectra to calculate ('13)CO and H(,2) column densities via the Local Thermodynamic Equilibrium approximation, and by star counting regions of POSS prints containing the clouds. Column densities are analyzed by modeling cloud local density distributions as power-laws (rho) (alpha) r('-(gamma)). Six of eight cloud envelopes are characterized by (gamma) (TURN) 2; the star-forming cloud CRL 437 has (gamma) (TURN) 3, while the elongated rotating cloud L1257 has (gamma) (TURN) 1 in its equatorial plane. Using estimated cloud distances and (gamma)'s, local H(,2) densities throughout the envelopes are inferred. Densities are low {n(H(,2)) < 300 cm(' -3)} over most of a cloud's volume, so that ambient UV radiation may not be significantly attenuated in these regions, possibly allowing gas temperatures to rise to 70 - 90 K near the cloud edge. Implications of such density and temperature structures are considered. Theories of globule evolution are reviewed in light of cloud angular momentum contents calculated in this study and found in the literature. Crude numerical results of sequential fragmentation theory can account for many inferred properties of globules, e.g. the correlation between cloud masses and specific angular momenta, and the reduction in average cloud angular momentum after several fragmentation epochs. Magnetic braking of cloud rotation is considered. Its importance for globule evolution is presently difficult to assess due to a paucity of observational constraints on field properties. However, it appears that fields are more likely to be important for cloud evolution if lateral field compression is delayed until a cloud's density has risen well above the ambient value.