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Session 115 - Star Clusters & Dwarf Galaxies.
Oral session, Saturday, January 10

[115.02] IZw18: A Complex Metal-poor Galaxy

D. de Mello (STScI), J. Heldmann (Colgate U.), D. Schaerer, C. Leitherer (STScI)

IZw18 is the most metal-poor star-forming galaxy known and for many decades it was thought to be the best example of a starburst from a primordial HI cloud. However, in the past few years HST images and high signal-to-noise ground based spectra have revealed a complete different scenario for IZw18. It has even been suggested that the present burst of star formation in IZw18 may not be the first one in its lifetime. Moreover, the presence of Wolf-Rayet stars in such a low metallicity environment will be an important constraint on theories of massive star evolution. We have used archival HST images to study the stellar and gaseous spatial distribution in IZw18. We have created HeII, [OIII], H\alpha and continuum maps and analysed the excitation conditions of the gas. The HeII map and the most recent ground based spectroscopy from the literature were used in order to distinguish between HeII nebular emission and stellar emission.

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