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Title: Feedback in star cluster formation
Author: Dale, J. E.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2004
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Massive stars emit strong fluxes of ionising radiation and their dynamical impact on their natal clusters is expected to be severe. The outflows generated expel residual gas from the cluster and can potentially gravitationally disrupt it. The loss of its reserves of molecular gas also prevents the cluster forming more stars. Star-formation and star cluster evolution cannot be fully understood without a proper treatment of feedback. I present a novel technique I have developed to allow the inclusion of the effects of ionising radiation in smoothed particle hydrodynamics (SPH) simulations of star clusters. The new algorithm is able to reproduce the results of simple analytical models and also gives results in good agreement with a more sophisticated Monte Carlo radiative transfer code when tested under highly anisotropic conditions. I simulate the effects of ionising radiation in globular clusters and compare my results with one-dimensional calculations with which I find good agreement. I investigate three cases in which different quantities of gas are distributed in my model cluster such that the as becomes fully ionised either during the HII region’s formation phase, or during its expansion phase, or such that the HII region is trapped inside the cluster core. I find gas expulsion to be quite efficient in the calculations in which the HII region escapes the core. I observe an instability in the second calculation which causes the shocked shell driven by the ionisation front to fragment as the HII region exits the core. The instability produces new structure from the smooth gas in the system, but this structure is rapidly destroyed by the radiation field and the effect of the instability on the evolution of the system is minimal. I also simulate feedback in the context of young embedded clusters, a highly inhomogeneous and anisotropic environment. I find that, again, photoionisation is able to produce novel structure in the ambient gas, causing it to fragment into filaments and beads. This fragmentation of the neutral gas, together with compression by hot ionised gas, which decreases the Jeans mass, lead me to conclude that feedback promotes star formation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available