The ionizing starbirth activity in M101, M82, and NGC 1569 has been investigated via CCD imagery at H$\alpha$, R, I, and (SIII) bands. The three galaxies are compared with one another and with M51, M83, and the Milky Way in terms of their starbirth intensities, starbirth efficiencies, and possible starbirth histories. The globally-averaged starbirth intensities that are inferred from the extinction-corrected H$\alpha$ surface brightnesses vary by $\sim$3 orders of magnitude, with M101 and the Milky Way defining the low end and with M82 defining the high-intensity regime. The annular-averaged starbirth intensities correlate strongly with the H$\sb2$ surface densities and with the total gas surface densities, where near-linear relationships are obtained. Unusually high starbirth efficiencies and eruptive gaseous morphologies are evident in M82, NGC 1569, and NGC 5461--one of the supergiant HII region complexes in M101. Crude indices of the galaxies' starbirth histories indicate temporally declining starbirth intensities in M101 and the Milky Way but currently "bursting" starbirth intensities in M82 and NGC 1569. In M101, annular-averaged photometry of the H$\alpha$ emission yields a much flatter galactocentric profile of surface brightness than that of the red-continuum starlight. The corresponding e-folding scale lengths are 9 and 3.3 kpc. respectively, thus implying significant differences between the galactocentric distributions of current-epoch massive star formation and past-averaged star formation. Moreover, the giant HII regions in M101 show significant variations in H$\alpha$ equivalent width as a function of both galactocentric radius and H$\alpha$ luminosity. These variations can be attributed to changes in the upper stellar mass limits of the ionizing clusters--M(upper) increasing in the outer galaxy, where the brighter HII regions are more numerous. The galactocentric variation in H$\alpha$ equivalent widths appears more closely related to the galaxy's radial profile of differential rotation than to its monotonic gradient in O/H abundances. The ionizing stellar populations in early-type, late-type, and starburst galaxies are discussed in terms of these results.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:dissertations-7968 |
| Date | 01 January 1990 |
| Creators | Waller, William Howard |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Language | English |
| Detected Language | English |
| Type | text |
| Source | Doctoral Dissertations Available from Proquest |
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