Polarimetry of the irregular galaxy m82

Abstract

This thesis contains an account of some of the work undertaken by the author while a member of the Astronomy Group at the University of Durham. The work of the group which involves the measurement of the amount of linear polarisation in nebular astronomical objects, is in collaboration with the Royal Greenwich Observatory. The initial chapters of the thesis describe the design and construction of the Durham Polarimeter which detects and measures the polarisation, and outlines the advantages of using a 4 cm McMullan electronographic camera as a recording device Initial alignment of the polarimcter components prior to observation and the procedures followed to obtain a series of electronographic plates are described along with the development of a series of reduction equations which link the polarisation parameters to the densities of the images on the electronographic plates. Electronographs of the irregular II galaxy, M82, which is the subject of study in this thesis are illustrated. In the later chapters of the thesis, the 1 education of the visual electronograplis to a digital form and the subsequent sophisticated computer programming required to accurately align the digital electronographs, lead out the densities for several thousand locations distributed over the lunge of the galaxy, and finally convert these densities to polarisation parameters is described. Comparison of the new polarisation map of 1182, with the previous photo-electric determinations confirms the success of this new automatic technique for the production of high resolution, accurate polarimetric measurements. In the final chapters of this thesis, M82 is reviewed chronologically, and the observational information on the galaxy is summarised. Finally, the present polarisation data is analysed using a recent model of the galaxy, and the result which are consistent with those previously determined are considered in conjunction with the mass of observational evidence concerning the evolution and morphology of the galaxy. The possibility that M82 may represent a connecting link in galactic evolution is tentatively proposed.