The development of new methods for high resolution radio astronomy imaging

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dc.contributor.advisor Gabuzda, Denise en Coughlan, Colm P. 2015-08-19T14:13:12Z 2015-08-19T14:13:12Z 2014 2014
dc.identifier.citation Coughlan, C. P. 2014. The development of new methods for high resolution radio astronomy imaging. PhD Thesis, University College Cork. en
dc.identifier.endpage 294
dc.description.abstract Very Long Baseline Interferometry (VLBI) polarisation observations of the relativistic jets from Active Galactic Nuclei (AGN) allow the magnetic field environment around the jet to be probed. In particular, multi-wavelength observations of AGN jets allow the creation of Faraday rotation measure maps which can be used to gain an insight into the magnetic field component of the jet along the line of sight. Recent polarisation and Faraday rotation measure maps of many AGN show possible evidence for the presence of helical magnetic fields. The detection of such evidence is highly dependent both on the resolution of the images and the quality of the error analysis and statistics used in the detection. This thesis focuses on the development of new methods for high resolution radio astronomy imaging in both of these areas. An implementation of the Maximum Entropy Method (MEM) suitable for multi-wavelength VLBI polarisation observations is presented and the advantage in resolution it possesses over the CLEAN algorithm is discussed and demonstrated using Monte Carlo simulations. This new polarisation MEM code has been applied to multi-wavelength imaging of the Active Galactic Nuclei 0716+714, Mrk 501 and 1633+382, in each case providing improved polarisation imaging compared to the case of deconvolution using the standard CLEAN algorithm. The first MEM-based fractional polarisation and Faraday-rotation VLBI images are presented, using these sources as examples. Recent detections of gradients in Faraday rotation measure are presented, including an observation of a reversal in the direction of a gradient further along a jet. Simulated observations confirming the observability of such a phenomenon are conducted, and possible explanations for a reversal in the direction of the Faraday rotation measure gradient are discussed. These results were originally published in Mahmud et al. (2013). Finally, a new error model for the CLEAN algorithm is developed which takes into account correlation between neighbouring pixels. Comparison of error maps calculated using this new model and Monte Carlo maps show striking similarities when the sources considered are well resolved, indicating that the method is correctly reproducing at least some component of the overall uncertainty in the images. The calculation of many useful quantities using this model is demonstrated and the advantages it poses over traditional single pixel calculations is illustrated. The limitations of the model as revealed by Monte Carlo simulations are also discussed; unfortunately, the error model does not work well when applied to compact regions of emission. en
dc.description.sponsorship Irish Research Council for Science Engineering and Technology (EMBARK, IDRS/2010/2105) en
dc.format.mimetype application/pdf en
dc.language.iso en en
dc.publisher University College Cork en
dc.rights © 2014, Colm P. Coughlan. en
dc.rights.uri en
dc.subject Radio astronomy en
dc.subject Active galactic nuclei en
dc.subject Maximum entropy method en
dc.subject Radio imaging en
dc.subject High resolution radio astronomy en
dc.title The development of new methods for high resolution radio astronomy imaging en
dc.type Doctoral thesis en
dc.type.qualificationlevel Doctoral en
dc.type.qualificationname PhD (Science) en
dc.internal.availability Full text available en No embargo required en
dc.description.version Accepted Version
dc.contributor.funder Irish Research Council for Science Engineering and Technology en
dc.description.status Not peer reviewed en Physics en
dc.check.type No Embargo Required
dc.check.reason No embargo required en
dc.check.opt-out No en
dc.thesis.opt-out false
dc.check.embargoformat Not applicable en
dc.internal.conferring Autumn Conferring 2014

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© 2014, Colm P. Coughlan. Except where otherwise noted, this item's license is described as © 2014, Colm P. Coughlan.
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