AAS 195th Meeting, January 2000
Session 90. Gas in Galaxies
Oral, Friday, January 14, 2000, 10:00-11:30am, Regency VII

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[90.05] Giant HII Regions in M33

B. P. Skelton (Marietta, GA)

In my dissertation I examine seven giant HII regions (GHRs) in the nearby spiral galaxy M33. These GHRs were chosen because they span a range in metallicity and galactocentric distance. Ground-based optical observations of the emission lines H\alpha, H\beta, [SII], and [OIII] were obtained at the Apache Point Observatory 3.5-m telescope. Images of NGC 604, NGC 595, NGC 588, IC 133, IC 142, MA 1, and CC 93 at these wavelengths are presented. H\alpha/H\beta, [SII]/H\alpha, and [OIII]/H\beta ratio maps are constructed from the data in order to study the reddening of the GHRs, shock excited gas within them, and the excitation of the photoionized gas, respectively.

Infrared properties of all of these GHRs except CC 93 are studied by means of HIRAS deconvolved IRAS observations of M33. The spectral energy distributions are compared, and the color temperature of the dust is determined.

In addition, three of the GHRs, IC 133, NGC 595, and CC 93, have been observed with ISO. Spectral imaging of these regions with ISOCAM CVF scans from 5 to 16 \mum show lines and bands of atomic and dust emission. The dust is in very different states in each of these regions, ranging from very hot and close to the ionizing stars in IC 133 to cool and far from the stars in CC 93.

The ultraviolet fluxes of the stellar populations of all the GHRs except MA 1 are measured from Astro-1 UIT images of M33 at 1520 Å\ and 2490 Å. A single-burst cluster model is used to predict the number of Lyman continuum photons produced by the observed stars; this number is compared with the number of Lyman continuum photons required to ionize the hydrogen resulting in the observed H\alpha emission.

The spectral energy distributions of two of the GHRs with well-studied stellar populations (based on WFPC-2 observations) are presented covering the wavelength range of 1500 Å\ to 21 cm. Model cluster spectra and dust emission are fitted to the SEDs. Finally, the star formation rates found for each of the seven GHRs by different methods are compared.

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