Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.645034
Title: The sizes of HII regions in external galaxies
Author: Coulson, I. M.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1980
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Abstract:
Calibrated photographs in the light of Ha + [NII] have been obtained for ten southern spiral galaxies, primary amongst them being M83 (NGC 5236) for which there are six plates, four from the United Kingdom 48" Schmidt Telescope (UKST) and two from the Anglo-Australian Telescope (AAT). The HII regions in these galaxies are identified and measured with the automatic plate measuring machine, COSMOS, at the Royal Observatory, Edinburgh. The sizes of the HII regions are determined from the measured profiles suitably deconvolved by the instrumental profile as given by the stellar intensity profiles. The dimensions obtained are a function of the assumed intrinsic intensity profiles of the HII regions. The assumption that these are gaussians leads to a systematic difference in the determined sizes and could systematically affect the value of Ho, the Hubble Constant. The correct choice of intrinsic intensity profile is defined as that which removes the systematic effect. For M83 this is found to be an exponential decay profile. The dimensions of the HII regions are derived and the resulting size distribution is found to be well fit by a Poisson function, the parameterisation of which is proposed as a distance indicator. It is shown to be free from effects due to selection by brightness and represents the 'giant' HII regions that define the spiral arms. Other galaxies studied also have HII region size distributions that could be fit by Poisson functions. A comparison of the HII region size distributions of M33 and M83 gives a distance for the latter of about 4 Mpc and an estimate of H0 of 80 Ion s-1 Mpc-1.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.645034  DOI: Not available
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