Star formation in the Perseus molecular cloud: observations of dynamics and comparison to simulations




Kirk, Helen Marjorie

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The relative importance of physical processes occurring on the various scales within molecular clouds is strongly debated, partly due to the lack of systematic cloud-wide observations available until recently. My thesis characterizes the kinematics of star formation across the entire Perseus molecular cloud as well as in a suite of simulations, providing statistical measures that successful theories of star formation will have to explain. My thesis consists of three interconnected projects described below. Dense core survey: The kinematics of the dense cores in Perseus were measured through single pointing observations of the N2H+(1–0) and C18O(2–1) transitions, tracing the dense core gas and surrounding lower density gas respectively. The internal velocity dispersion of the dense cores was observed to be small – dominated by thermal motions, and roughly the size expected for the cores to be in virial equilibrium. The dense cores also have little motion with respect to the surrounding low density gas – usually much less than the ambient sound speed of the medium. Comparison to cloud survey: The dense core observations were compared to a full spectral cube of 13CO(1–0) emission from the COMPLETE Survey, tracing the lower-density cloud material. From this analysis, it was determined that the dense cores have little motion with respect to the larger structures that they inhabit – smaller than the typical velocity dispersion or the estimated virial velocity dispersion of the region. Analysis of simulations: A suite of thin-sheet MHD simulations with varying levels of input magnetic field strengths and turbulence were analyzed in a manner to mimic the above observational surveys. While the small internal velocity dispersion of the dense cores could be reproduced by most of the simulations, the small motion between the core and its surrounding lower density gas could not be produced at the same time as the observed large-scale non-thermal motions. Future directions: The kinematic measures presented here will be straightforward to apply to future multi-cloud surveys as well as other numerical simulations. This will allow the effect of environment on star formation to be better explored in both the observational and simulated domains.



Stars, Formation, Molecular clouds