Barnes, DJ; (2015) Origin and Evolution of Large-scale Magnetic Fields. Doctoral thesis , UCL (University College London).

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Abstract

Magnetic elds are ubiquitous at all scales in the Universe and have been observed in galaxies and clusters of galaxies via observations of di use radio emission and Faraday Rotation Measures. Despite the observations, the origin and impact of the magnetic elds in these systems is poorly understood. In this thesis we develop a state of the art cosmological Smoothed Particle Magnetohydrodynamics code, GCMHD+, to enable the study of the magnetic elds of the largest bound structures in the Universe. Using a wide range of idealized test problems, we justify our choice of free parameters and demonstrate the performance of the code relative to analytical solutions and the results produced by a grid based MHD scheme. We then used the code to investigate the evolution of a seed magnetic eld due to the formation of structure. By varying the numerical scheme, we demonstrate that the growth of magnetic elds in galaxy clusters are very sensitive to the growth of numerical divergence of the magnetic eld. We nd that amplitude and topology of the cluster magnetic eld are insensitive to the mass or formation history of the cluster. Using high resolution simulations, we show that a primordial seed magnetic eld is capable of reproducing a wide range of observations of large-scale magnetic elds in galaxy clusters. Additionally, we examine the impact of the formation of spiral structure in a disc galaxy on the galactic magnetic eld. We nd that the numerical scheme can become unstable unless the divergence cleaning scheme is limited. We nd that the rotation of the galaxy produces a disc orientated magnetic eld with a spiral structure and large-scale eld reversals. The formation of spiral arms ampli es the ambient G magnetic eld to 20 G, in agreement with the observations of spiral galaxies. We conclude that additional physics is required to produce a more realistic galactic magnetic eld.

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