A New Age and Distance for I Zw 18, the Most Metal-Poor Galaxy in the Nearby Universe
Abstract
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.
- Publication:
-
Low-Metallicity Star Formation: From the First Stars to Dwarf Galaxies
- Pub Date:
- December 2008
- DOI:
- 10.1017/S174392130802512X
- Bibcode:
- 2008IAUS..255..387A
- Keywords:
-
- galaxies: dwarf;
- galaxies: starburst;
- galaxies: evolution;
- galaxies: stellar content;
- galaxies: distances;
- galaxies: redshifts;
- galaxies: individual (I Zw 18);
- (stars: variables:) Cepheids