On the largest scale, the Universe resembles a cosmic spiderweb. Most galaxies coexist in small groups within the threads of this web. At the nodes of the threads are enormous groups of galaxies... Show moreOn the largest scale, the Universe resembles a cosmic spiderweb. Most galaxies coexist in small groups within the threads of this web. At the nodes of the threads are enormous groups of galaxies forming the largest structures in the universe still held together by gravity: clusters of galaxies.Clusters of galaxies consist of thousands of galaxies, although the galaxies constitute only a few per cent of the total cluster mass. The majority of the (non-dark) mass of a cluster is in a hot and dilute gas that resides in the space between galaxies and is permeated by magnetic fields. Clusters grow by collisions with other clusters, shocking and heating the gas causing amplification of magnetic fields and acceleration of particles to near the speed of light. This makes clusters a source of radio synchrotron radiation.This thesis investigates the particle acceleration process and the magnetic fields of merging clusters using the LOFAR and VLA radio telescopes. The thesis presents, among other things, one of the few radio maps of clusters at ultra-low frequencies and examines clusters of lower mass than usual. Additionally, the thesis includes observations of a sample of over a hundred clusters to statistically determine the properties of the magnetic field in clusters in a novel way. Show less
This thesis develops a method for direction dependent calibration of the ionosphere in radio interferometric data. The method uses the physical theory of the propagation of radio waves through a... Show moreThis thesis develops a method for direction dependent calibration of the ionosphere in radio interferometric data. The method uses the physical theory of the propagation of radio waves through a random weakly scattering medium, to construct a Gaussian process prior for differential total electron content. We develop a technique for applying this to real data, and apply the technique to several 8-hour LOFAR HBA observations. We find the method is able to, for the first time, remove the direction dependent effects of the ionosphere using a screen based approach. In the process we discover a direction dependent systematic in the data that places a limit of the efficacy of the method. Show less
