Chemical Abundance Distributions of Galactic Halos and their Satellite Systems in a Lambda CDM Universe

Details Chemical Abundance Distributions of Galactic Halos and their Satellite Systems in a Lambda CDM Universe Chemical Abundance Distributions of Galactic Halos and their Satellite Systems in a Lambda CDM Universe

2005-07-05

arxiv.org/abs/astro-ph/0507114v1

Astrophys.J.638:585-595,2006

Astronomy and Astrophysics

Astrophysics

submitted to ApJ

Scientific paper

10.1086/498970

We present a cosmologically motivated model for the hierachical formation of the stellar halo which includes a semi-analytic treatment of galactic chemical enrichment coupled to numerical simulations that track the orbital evolution and tidal disruption of satellites. A major motivating factor in this investigation is the observed systematic difference between the chemical abundances of stars in satellite galaxies and those in the Milky Way halo. Specifically, for the same [Fe/H] values, stars in neighboring satellite galaxies display significantly lower [alpha/Fe] ratios than stars in the halo. We find that the observed chemical abundance patterns are a natural outcome of the process of hierarchical assembly of the Galaxy. This result follows because the stellar halo in this context is built up from satellite galaxies accreted early on (more than 8-9 Gyr ago) and enriched in alpha-elements produced in Type II supernovae. In contrast, satellites which survive today are typically accreted late (within the last 4-5 Gyr) with nearly solar [alpha/Fe] values as a result of contributions from both Type II and Type Ia supernovae. We use our model to investigate the abundance distribution functions (using both [Fe/H] and [alpha/Fe] ratios) for stars in the halo and in surviving satellites. Our results suggest that the shapes and peaks in the abundance distribution functions provide a direct probe of the accretion histories of galaxies.

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