Carbon-Enhanced Metal-Poor Stars: Relics from the Dark Ages
  We use detailed nucleosynthesis calculations and a realistic prescription for
the environment of the first stars to explore the first episodes of chemical
enrichment that occurred during the dark ages. Based on these calculations, we
propose a novel explanation for the increased prevalence of carbon-enhanced
metal-poor (CEMP) stars with decreasing Fe abundance: The observed chemistry
for the most metal-poor Galactic halo stars is the result of an intimate link
between the explosions of the first stars and their host minihalo's ability to
retain its gas. Specifically, high-energy supernovae produce a near solar ratio
of C/Fe, but are effective in evacuating the gas from their host minihalo,
thereby suppressing the formation of a second generation of stars. On the other
hand, minihalos that host low-energy supernovae are able to retain their gas
and form a second stellar generation but, as a result, the second stars are
born with a supersolar ratio of C/Fe. Our models are able to accurately
reproduce the observed distributions of [C/Fe] and [Fe/H], as well as the
fraction of CEMP stars relative to non-CEMP stars as a function of [Fe/H]
without any free parameters. We propose that the present lack of chemical
evidence for very massive stars (>140 Msun), that ended their lives as a highly
energetic pair-instability supernova, does not imply that such stars were rare
or did not exist; the chemical products of these very massive first stars may
have escaped from their host minihalo, and were never incorporated into
subsequent generations of stars. Finally, our models suggest that the most
Fe-poor stars currently known may have seen the enrichment from a small
multiple of metal-free stars, and need not have been exclusively enriched by a
solitary first star. These calculations support the idea that some of the
surviving dwarf satellite galaxies of the Milky Way are relics of the first
galaxies.
