AAS 205th Meeting, 9-13 January 2005
Session 99 The Extragalactic ISM
Poster, Wednesday, January 12, 2005, 9:20am-6:30pm, Exhibit Hall

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[99.05] The Radial Variation of the Diffuse H-alpha Fraction in 12 Nearby Galaxies

E. S. Voges, R. A. M. Walterbos (NMSU)

The fractional contribution of the diffuse ionized gas (DIG) to a galaxy's total H-alpha flux has been observed to lie consistently between 30 and 50%, regardless of the galaxy's Hubble type or star formation rate. Brighter DIG regions tend to trace brighter HII regions; thus, studying a galaxy's diffuse H-alpha fraction may provide insight into whether HII regions may be leaking ionizing photons. We will study the diffuse H-alpha fraction across individual disks by looking at its variation with galactic radius. To complete this study we will use suitably deep H-alpha images of 12 nearby galaxies taken with the Kitt Peak National Observatory 0.9-m telescope. We hope to answer such questions as what role do massive stars in HII regions and field stars play in the ionization of the DIG at different radii? Additionally, how does the density of the gas (likely connected with the mean free path length of the ionizing photons) affect the diffuse fraction? Although the fraction of photons which leak out of HII regions seems rather constant among different galaxies, our study will reveal whether this fraction is constant across individual galaxies.

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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.