Schedule Feb 17, 2012
Progenitors of Ultra-Faint Dwarfs and the Milky Way Halo: Constraints from the Distributions of Neutron-Capture Elements
Duane Lee (Columbia Univ.)

Chemical abundance data exhibit remarkable agreement between the distributions of [α/Fe] ([(Ti, Ca, Mg)/Fe]) abundance ratios found in stars located in the Milky Way (MW) Halo and ultra-faint dwarf (UFD) galaxies. However, when contrasting the neutron-capture distributions [(Sr, Ba)/Fe], the peak of the small UFD sample (~ 20 stars) reveals a statistically-significant negative offset in abundance ratios when compared to the large MW sample (~ 1000 stars). In this study, we show that the apparent contradiction in neutron-capture distributions could be explained as the under-sampling of intrinsically-skewed distributions in UFDs. We emphasize that the UFDs' distributions can be achieved by simply appealing to stochastic pollution by star clusters that are systematically smaller than those in MW progenitors. Hence, there is no need to invoke other complex effects such as primordial abundance signatures, blowout of metals, and/or incomplete mixing.


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