Mathematics – Logic
Scientific paper
Oct 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999phdt........11t&link_type=abstract
Thesis (PhD). UNIVERSITY OF ALBERTA (CANADA), Source DAI-B 61/03, p. 1451, Sep 2000, 173 pages.
Mathematics
Logic
1
Scientific paper
This thesis presents a detailed study of the simulation of galaxy formation in the cold dark matter (CDM) cosmology. Smoothed Particle Hydrodynamics (SPH) is used to follow the hydrodynamics within the simulations and an analysis of the performance of twelve different implementations of SPH is presented. Seven tests are used which are designed to isolate key hydrodynamic elements of cosmological simulations. It is shown that the artificial viscosity is the single most important factor in determining results. The way in which force symmetry is achieved in the equation of motion has a secondary effect. Most results favour a kernel symmetrization approach. A detailed description of a method for simulating the formation of individual galaxies is given. Gas regions which fall within temperature, density, self- gravity and convergent-flow criteria are assumed to form stars. A Lagrangian Schmidt Law is used to calculate the star formation rate. Feedback from supernovae is incorporated by returning thermal energy to the inter- stellar medium. Radiative losses are prevented from heated particles by adjusting the radiative cooling mechanism. The model is tested on isolated disc galaxies as well as galaxies formed from cosmological initial conditions. A discussion is presented on the implementation of `HYDRA', a combined hydrodynamic and gravity N-body particle integrator, on shared-memory architectures with a symmetric multi- processor configuration (SMP). Parallelization is achieved using the directives in the OpenMP application program interface. The performance of the code is examined for up to 128 processors and excellent scaling is found, provided a large enough problem is studied. A high resolution simulation is presented which satisfies a number of criteria for accuracy defined in the SPH tests. Due to limitations of the parallel code it was not possible to integrate the simulation to the desired final epoch. At high resolution gas in-fall is seen to be highly unsmooth, and the gas appears to lose angular momentum more rapidly. Although higher resolution prevents the formation of very dense gas cores it does not entirely prevent the condensation of cold gas. Prospects for the future of the simulation field, and the CDM model of structure formation are given.
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