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One way to constrain the nature of the high-redshift progenitors of the MilkyWay is to look at the low-metallicity stellar populations of the differentGalactic components today. For example, high-resolution spectroscopy of verymetal poor (VMP) stars demonstrates remarkable agreement between thedistribution of [Ti/Fe] in the stellar populations of the Milky Way halo (MW)and ultra-faint dwarf (UFD) galaxies. In contrast, for the neutron capture (nc)abundance ratio distributions [(Sr,Ba)/Fe], the peak of the small UFD sample (6stars) exhibits a signicant under-abundance relative to the VMP stars in thelarger MW halo sample (~ 300 stars). We present a simple scenario that cansimultaneously explain these similarities and differences by assuming: (i) thatthe MW VMP stars were predominately enriched by a prior generation of starswhich possessed a higher total mass than the prior generation of stars thatenriched the UFD VMP stars; and (ii) a much stronger mass-dependent yield (MDY)for nc-elements than for the (known) MDY for Ti. Simple statistical testsdemonstrate that conditions (i) and (ii) are consistent with the observedabundance distributions, albeit without strong constraints on model parameters.A comparison of the broad constraints for these nc-MDY with those derived inthe literature seems to rule out Ba production from low-mass SNs and affirmsmodels that primarily generate yields from high-mass SN. Our scenario can beconfirmed by a relatively modest (factor of ~ 3-4) increase in the number ofhigh-resolution spectra of VMP stars in UFDs.

A Mass-Dependent Yield Origin of Neutron-Capture Element Abundance Distributions in Ultra-Faint Dwarfs