The development of new methods for high resolution radio astronomy imaging

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dc.check.embargoformatNot applicableen
dc.check.infoNo embargo requireden
dc.check.opt-outNoen
dc.check.reasonNo embargo requireden
dc.check.typeNo Embargo Required
dc.contributor.advisorGabuzda, Deniseen
dc.contributor.authorCoughlan, Colm P.
dc.contributor.funderIrish Research Council for Science Engineering and Technologyen
dc.date.accessioned2015-08-19T14:13:12Z
dc.date.available2015-08-19T14:13:12Z
dc.date.issued2014
dc.date.submitted2014
dc.description.abstractVery 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.sponsorshipIrish Research Council for Science Engineering and Technology (EMBARK, IDRS/2010/2105)en
dc.description.statusNot peer revieweden
dc.description.versionAccepted Version
dc.format.mimetypeapplication/pdfen
dc.identifier.citationCoughlan, C. P. 2014. The development of new methods for high resolution radio astronomy imaging. PhD Thesis, University College Cork.en
dc.identifier.endpage294
dc.identifier.urihttps://hdl.handle.net/10468/1924
dc.language.isoenen
dc.publisherUniversity College Corken
dc.rights© 2014, Colm P. Coughlan.en
dc.rights.urihttp://creativecommons.org/licenses/by-nc-nd/3.0/en
dc.subjectRadio astronomyen
dc.subjectActive galactic nucleien
dc.subjectMaximum entropy methoden
dc.subjectRadio imagingen
dc.subjectHigh resolution radio astronomyen
dc.thesis.opt-outfalse
dc.titleThe development of new methods for high resolution radio astronomy imagingen
dc.typeDoctoral thesisen
dc.type.qualificationlevelDoctoralen
dc.type.qualificationnamePhD (Science)en
ucc.workflow.supervisord.gabuzda@ucc.ie
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