Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21341911s&link_type=abstract
American Astronomical Society, AAS Meeting #213, #419.11; Bulletin of the American Astronomical Society, Vol. 41, p.235
Astronomy and Astrophysics
Astronomy
2
Scientific paper
We report on results of new deep imaging obtained with the Hubble Space Telescope (HST) Advance Camera for Surveys (ACS) that show the Leo I dwarf Spheroidal (dSph) galaxy has a much larger population of ancient (>10 Gyr old) stars than previously determined with shallower WFPC2 imaging (Gallart et al. 1999, Dolphin 2003), as well as the previously identified component of intermediate-aged stars. Our new imaging is much deeper, which allows us to unambiguously identify the main sequence turnoffs of the ancient population and constrain the star formation rate at the epoch of the formation of the "first stars” in this galaxy. We will determine the galaxy's star formation rate as a function of time from the observed density of stars in the color-magnitude diagram by comparing with Padova stellar evolutionary models (Girardi et al. 2000). We compare and contrast the star formation histories of the Leo I dSph, which is currently devoid of any gas, with that of the gas-rich Leo A dIrr galaxy. The two are very different in that the dSph formed most of its stars early and the dIrr formed most of its stars later, however both have been actively forming stars over most of the age of the universe.
Bullock James
Cole Andrew A.
Gallagher Jay S.
Marsteller Brian
Smecker-Hane Tammy Ann
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