With its extremely low metallicity (˜1/50 solar), blue colors, and high gas content, the blue compact dwarf (BCD) I Zw 18 has often been indicated as the best candidate for a truly ``primordial'' galaxy in the nearby Universe. Nevertheless, recent studies from our group based on deep HST/ACS data have demonstrated the presence of red giant branch stars in this system, implying that star formation was active at least 1 Gyr ago, and possibly back to a Hubble time. At the light of these results, two possibilities remain open to explain the low metallicity observed in this system, i.e. a) for the majority of the galaxy' s life the star formation rate was very low and thus the chemical enrichment was inefficient, or b) strong galactic winds were able to remove the metals. Deriving the star formation history (SFH) of IZw18 is a fundamental step to answer these questions and to provide constraints on chemical evolution and hydrodynamical models of metal-poor galaxies. Here we present our new results on the SFH of I Zw 18 based on the method of the synthetic color magnitude diagrams.
The star formation history of the BCD I Zw 18
Cignoni, M.;
2015-01-01
Abstract
With its extremely low metallicity (˜1/50 solar), blue colors, and high gas content, the blue compact dwarf (BCD) I Zw 18 has often been indicated as the best candidate for a truly ``primordial'' galaxy in the nearby Universe. Nevertheless, recent studies from our group based on deep HST/ACS data have demonstrated the presence of red giant branch stars in this system, implying that star formation was active at least 1 Gyr ago, and possibly back to a Hubble time. At the light of these results, two possibilities remain open to explain the low metallicity observed in this system, i.e. a) for the majority of the galaxy' s life the star formation rate was very low and thus the chemical enrichment was inefficient, or b) strong galactic winds were able to remove the metals. Deriving the star formation history (SFH) of IZw18 is a fundamental step to answer these questions and to provide constraints on chemical evolution and hydrodynamical models of metal-poor galaxies. Here we present our new results on the SFH of I Zw 18 based on the method of the synthetic color magnitude diagrams.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
