Parsec-scale structure in star-forming molecular clouds (Bipolar outflows).

摘要

In this thesis, I present high resolution, fully-sampled 12CO and 13CO surveys of Orion A, the Perseus giant molecular cloud, and two smaller clouds: L1551 and Circinus. The large scale structure in these molecular clouds appears to be shaped by energy injection from neighboring OB associations through their UV radiation, winds, and supernovae. The small scale structure of these clouds appears to be shaped by energy injection by outflows from young stellar objects, HII regions, and gravity. I study in detail outflow properties and their impact on the host clouds. I introduce a technique of mass estimation which accounts for the velocity dependence of the ratio of isotopic opacities for like rotational transitions. This technique has the effect of steepening the mass spectra of outflows by up to 50% in the high velocity wings. Finally I investigate the statistical properties of star-forming regions.; The specific results of the thesis are listed here. (1) L1551 appears to be a cometary cloud which is marked by about a dozen overlapping outflows. The main bipolar outflow is energetically supported by at least three outflows; two from L1551 IRS5 and one (possibly two) from L1551 NE. The very prominent low velocity east--west mono-polar outflow has a well-defined, limb-brightened cavity that points back toward the IRS5 and L1551NE sources; no direct evidence has been found that either source drives this flow. (2) The morphology of the Circinus molecular cloud is being shaped by at least ten currently active outflows. (3) The large scale structure and kinematics of the Perseus giant molecular cloud appears to be driven by the neighboring OB2 association. I present evidence that the star-forming clouds within the complex are not gravitationally bound to each other. Currently active outflows from young stellar objects can provide the requisite energy injection to sustain observed turbulent motions. I show that a model of super-alfvenic random flows provides a superior description of the cloud statistics than that of magneto-hydrodynamic flows. (4) The large scale structure and kinematics of the Orion A cloud appears to be driven by the Orion OB1a & b associations located to the north of the cloud. The small scale structure ( ≲ 5 parsecs) is being driven by influence of outflows, the blister H II region, and gravity. There are dozens of young stellar objects driving overlapping outflows which run the length of the cloud. One of the largest, the BN/KL outflow has produced a ∼2 pc bipolar cavity to the northwest and southeast with a collimation of ∼2.; These star-forming clouds are evidently driven by energy injection on many scales. This contrasts the theory that molecular clouds are fundamentally fractal in nature, wherein spatial and kinematic structure is the result of a turbulent cascade from some large-scale energy injection mechanisms down to the subparsec scale.