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Extremely Metal-Poor Dwarf Galaxies: The HI Content

Mercedes E. Filho

Dwarf galaxies in the local volume outnumber normal galaxies by up to two orders of magnitude and are expected to be ubiquitous in the early Universe. According to our current theoretical view, these systems had been the "building blocks" of normal galaxies and played a key role in the chemical enrichment of the Universe as early as in the epoch of reionization. Whereas the bulk of dwarf galaxies in the nearby cosmos are composed of old stars, there is a tiny fraction of extremely gas-rich nearby dwarfs with no evidence for a dominant old stellar component. These systems are currently undergoing a major starburst episode and show extremely low metallicity in their ionized gas component. In fact, these so-called XBCDs are the most metal-poor emission-line galaxies known, and the best local analogs to the first generation of low-mass galaxies formed early on in the Universe. An intriguing property of XBCDs is their unusual optical morphology: other than old, high-metallicity dwarfs, these irregular systems are characterized by off-center star-forming activity, or cometary morphology. Interestingly, recent deep imaging studies of high-z galaxies with the HST reveal a similarly large fraction of cometary galaxies among young extragalactic systems at high z.
We have embarked on the study of the neutral gas (HI) content in a sample of local extremely metal-poor dwarf galaxies. This data have been combined with ancillary optical and velocity information. We here present our first results, which help shed some light on the global properties of these intriguing sources.

2013 April 03, 13:30

Centro de AstrofÝsica da Universidade do Porto (Auditorium)
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