Chemistry of the Most Metal-poor Stars in the Bulge and the z > 10
  Universe
  Metal-poor stars in the Milky Way are local relics of the epoch of the first
stars and the first galaxies. However, a low metallicity does not prove that a
star formed in this ancient era, as metal-poor stars form over a range of
redshift in different environments. Theoretical models of Milky Way formation
have shown that at constant metallicity, the oldest stars are those closest to
the center of the Galaxy on the most tightly-bound orbits. For that reason, the
most metal-poor stars in the bulge of the Milky Way provide excellent tracers
of the chemistry of the high-redshift universe. We report the dynamics and
detailed chemical abundances of three stars in the bulge with [Fe/H]
$\lesssim-2.7$, two of which are the most metal-poor stars in the bulge in the
literature. We find that with the exception of scandium, all three stars follow
the abundance trends identified previously for metal-poor halo stars. These
three stars have the lowest [Sc II/Fe] abundances yet seen in $\alpha$-enhanced
giant stars in the Galaxy. Moreover, all three stars are outliers in the
otherwise tight [Sc II/Fe]-[Ti II/Fe] relation observed among metal-poor halo
stars. Theoretical models predict that there is a 30% chance that at least one
of these stars formed at $z\gtrsim15$, while there is a 70% chance that at
least one formed at $10 \lesssim z \lesssim 15$. These observations imply that
by $z\sim10$, the progenitor galaxies of the Milky Way had both reached [Fe/H]
$\sim-3.0$ and established the abundance pattern observed in extremely
metal-poor stars.
