Global and Local Properties of Noninteracting Irregular Galaxies
Hunter, Deidre Ann
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https://hdl.handle.net/2142/70659
Description
Title
Global and Local Properties of Noninteracting Irregular Galaxies
Author(s)
Hunter, Deidre Ann
Issue Date
1982
Department of Study
Astronomy
Discipline
Astronomy
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Astronomy and Astrophysics
Abstract
In order to investigate the star formation processs controlling the evolutionary histories of noninteracting irregular galaxies, we have obtained optical and radio data on global and local scales for a sample of 26 irregulars with high star formation rates (SFR) and 17 comparison objects. Global properties of the systems were explored through the stellar and gaseous contents and abundances obtained from intermediate band filter photometry, large aperture spectrophotometry, small aperture spectrophotometry of individual H II regions, and H I 21-cm observations. The gas and abundance parameters, combined with other derived quantities such as the SFR, the fraction of a galaxy involved in the current star forming activity, and the time scale to exhaust the gas, were compared to predictions of global models of galaxy evolution: the closed system, stochastic star induced star formation, and gas infall models. In addition, large-aperture spectra of a sample of low-luminosity irregulars were obtained which provided a comparison to dwarf systems with low rates of star formation.
The investigation of the emission regions was based on measurements of local ionized gas kinematics through high dispersion spectra and on explorations of the spatial structure and distribution of star forming regions from direct imaging with a video camera through b,y,I, and H(alpha) passbands. These data were used to estimate the mechanical energy that is being returned to the interstellar medium from massive stars in the form of motions of ionized gas, diameters of distinct star forming regions, distances between H II regions, and the presence of dark clouds. These results were used to place constraints on the global star formation mechanisms in space and time and were compared to models for propagation of star formation. The results on both global and local scales were used to develop a general picture of the evolutionary histories of irregular galaxies.
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