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Title: Instabilities in supersonic cloud-cloud collisions
Author: McLeod, Andrew
ISNI:       0000 0004 2734 3863
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2012
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We study the effects of the supersonic collision of molecular clouds using smoothed particle hydrodynamics (SPH) simulations. We review the observational evidence for cloud-cloud collision and previous computational work. We describe the SPH method, the algorithms used in the SPH code SEREN, and how we have extended the parallelization of SEREN. We review the non-linear thin shell instability (NTSI) and gravitational instability in a shock-compressed layer. We present the results of two sets of SPH simulations. In the first set of simulations we collide supersonic flows of gas without self-gravity. We impose a range of velocity perturbations, including monochromatic perturbations, white noise perturbations and both subsonic and supersonic turbulence. The colliding flows create a dense shock-compressed layer which is unstable to the NTSI. We examine the effect of the differing initial perturbations on the NTSI, and calculate rates of growth of both bending modes and breathing modes as a function of time and wavenumber. We compare our results to the time-independent result predicted by Vishniac (1994) for a one-dimensional monochromatic perturbation, and examine how this result can be extended to two-dimensional perturbations and non-monochromatic perturbations. In our second set of simulations we model the head-on supersonic collision of two identical uniform-density spheres. We include self-gravity, allowing the dense layer to become gravitationally unstable and produce stars. We explore the effect of increasing collision velocity, and show that the NTSI is present only at higher collision velocities. At the highest collision velocities the NTSI severely disrupts the layer, and the collision does not produce stars. Although the global properties of the collision, such as the thickness of the layer, the size of the star-forming region and the time of first star formation, depend on the collision velocity, most individual properties of the stars do not.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QB Astronomy ; QC Physics