Astronomy and Astrophysics – Astrophysics – Galaxy Astrophysics
Scientific paper
2010-11-23
2011 ApJ, 727, 79
Astronomy and Astrophysics
Astrophysics
Galaxy Astrophysics
28 pages, 14 figures; accepted for publication in ApJ; very minor editorial corrections in v3
Scientific paper
10.1088/0004-637X/727/2/79
We derive the star formation histories of eight dwarf spheroidal (dSph) Milky Way satellite galaxies from their alpha element abundance patterns. Nearly 3000 stars from our previously published catalog (Paper II) comprise our data set. The average [alpha/Fe] ratios for all dSphs follow roughly the same path with increasing [Fe/H]. We do not observe the predicted knees in the [alpha/Fe] vs. [Fe/H] diagram, corresponding to the metallicity at which Type Ia supernovae begin to explode. Instead, we find that Type Ia supernova ejecta contribute to the abundances of all but the most metal-poor ([Fe/H] < -2.5) stars. We have also developed a chemical evolution model that tracks the star formation rate, Types II and Ia supernova explosions, and supernova feedback. Without metal enhancement in the supernova blowout, massive amounts of gas loss define the history of all dSphs except Fornax, the most luminous in our sample. All six of the best-fit model parameters correlate with dSph luminosity but not with velocity dispersion, half-light radius, or Galactocentric distance.
Cohen Judith Gamora
Guhathakurta Puragra
Kirby Evan N.
Majewski Steven R.
Smith Graeme H.
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