Thesis (M. Phil.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 102-111) Also available in print.

Thesis (PH. D.)--University of Chicago, 1917. / "Publications of the Yerkes observatory, vol. IV, part II."

Thesis (Ph. D.)--University of Wisconsin--Madison, 1983. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 53-58).

Using the 26 m paraboloid at the Dominion Radio Astrophysical Observatory, sufficient 21-cm line data have been obtained on thirteen dense dust clouds to give a measure of the significance of an excess or a deficit in the hydrogen emission from these objects, as compared with nearby surrounding regions of the sky. The analysis of these data indicates that four of these clouds show significant decreases in the hydrogen emission. If the widths of these deficits are to be interpreted as thermal broadening within a single cloud, kinetic temperatures obtained are far in excess of those indicated by normal OH emission from these same objects. If the OH and H are in thermodynamic equilibrium and the chemical abundances are normal, it is thought that the deficits are due to the hydrogen being in molecular form. However, measurements of higher spatial and velocity resolution are needed to rule out the possibility of a cold absorbing cloud. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The formation of spectral lines in the radio region from galactic nebulae is studied. Equations describing the strengths of these lines are developed for both the local thermodynamic equilibrium case and the statistical equilibrium case. An experiment in which radio lines from galactic nebulae were detected is described. The reduction of the observations to obtain estimates of the temperature and density of the galactic gas is performed, and comments on the validity of the analysis are included. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

published_or_final_version / Physics / Master / Master of Philosophy

“The nature of the nebulae and their place in the scheme of the universe have been favorite subjects of controversy since the very dawn of telescopic observations. In these later days, when the non-galactic nebulae have been clearly differentiated from the diffuse and the planetary, the discussion has concentrated around the spectacular forms of the spirals… island universes, scattered through the remote depths of space.” – Edwin P. Hubble It was only a mere 45 years ago, that some of the foremost astronomers such as Allan Sandage and Donald Lynden Bell believed that spiral galaxies were monolithic islands which were dynamically closed. This thesis has awaited the dawning of a new era wherein the disks of spiral galaxies can be “dust penetrated”. Prevalent ideas in the literature are overturned. Unprecedented images from IRAC onboard the Spitzer Space Telescope reveal the dynamic nature of nearby disk galaxies, including the two dominant spirals in our Local Group beyond the Milky Way. We show that M33 is a spiral galaxy whose disk grows outwards with time and which serves as a local Rosetta stone of a dynamically open system. We next show that the present-day morphology of M31 was induced only 210 million years ago. IRAC images betray its tumultuous recent past with the presence of two spectacular off-centre rings of dust, glowing at 8.0μm. A collision scenario seems most likely, with one of its larger satellite galaxies, M32. In our local universe, the bar phenomenon is ubiquitous. We separate bars from their parent disks in a sample of about 40 spiral galaxies, revealing that stronger spirals are not necessarily driven by stronger bars. Bars are not the universal excitation mechanism by which spiral structure is induced. Finally, surprising insights are gleaned from the IRAC 8.0μm window pertaining to the dust morphology of barred spirals. Three distinct form families of stellar bars are presented. May this thesis serve as “one small step for man” in our quest to expand our knowledge in the new epoch of quantitative galaxy classification in the dust-penetrated regime.

Thesis (M. Phil.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 88-95). Also available in print.

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Thesis (Ph. D.)--University of Wisconsin--Madison, 1963. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 120-125).