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A New Age and Distance for I Zw 18, the Most Metal-Poor Galaxy in the Nearby Universe

Published online by Cambridge University Press:  01 June 2008

A. Aloisi ,
G. Clementini ,
M. Tosi ,
F. Annibali ,
R. Contreras ,
G. Fiorentino ,
J. Mack ,
M. Marconi ,
I. Musella  and
A. Saha
...Show all authors
A. Aloisi
Affiliation:
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA email: [email protected] On assignment from the Space Telescope Division of the European Space Agency
G. Clementini
Affiliation:
INAF-Osservatorio Astronomico di Bologna, Via Ranzani 1, I-40127 Bologna, Italy
M. Tosi
Affiliation:
INAF-Osservatorio Astronomico di Bologna, Via Ranzani 1, I-40127 Bologna, Italy
F. Annibali
Affiliation:
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA email: [email protected]
R. Contreras
Affiliation:
INAF-Osservatorio Astronomico di Bologna, Via Ranzani 1, I-40127 Bologna, Italy
G. Fiorentino
Affiliation:
INAF-Osservatorio Astronomico di Bologna, Via Ranzani 1, I-40127 Bologna, Italy
J. Mack
Affiliation:
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA email: [email protected]
M. Marconi
Affiliation:
INAF-Osservatorio Astronomico di Capodimonte, Via Moiariello 16, I-80131 Napoli, Italy
I. Musella
Affiliation:
INAF-Osservatorio Astronomico di Capodimonte, Via Moiariello 16, I-80131 Napoli, Italy
A. Saha
Affiliation:
National Optical Astronomy Observatory, P.O. Box 26732, Tucson, AZ 85726
M. Sirianni
Affiliation:
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA email: [email protected] On assignment from the Space Telescope Division of the European Space Agency
R. P. van der Marel
Affiliation:
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA email: [email protected]
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Abstract

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The blue compact dwarf galaxy I Zw 18 holds the record of the lowest metallicity ever observed in the local universe. As such, it represents the closest analog to primordial galaxies in the early universe. More interestingly, it has recurrently been regarded as a genuinely young galaxy caught in the process of forming in the nearby universe. However, stars of increasingly older ages are found within I Zw 18 every time deeper high-resolution photometric observations are performed with the Hubble Space Telescope (HST): from the original few tens of Myrs to, possibly, several Gyrs. Here we summarize the history of I Zw 18 age and present an ongoing HST/ACS project which allowed us to precisely derive the galaxy distance by studying its Cepheid variables, and to firmly establish the age of its faintest resolved populations.

Keywords

galaxies: dwarfgalaxies: starburstgalaxies: evolutiongalaxies: stellar contentgalaxies: distancesgalaxies: redshiftsgalaxies: individual (I Zw 18)(stars: variables:) Cepheids
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 4 , Issue S255: Low-Metallicity Star Formation: From the First Stars to Dwarf Galaxies , June 2008 , pp. 387 - 391
Copyright
Copyright © International Astronomical Union 2008

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