The most metal-poor damped Lyman alpha systems: An insight into dwarf
  galaxies at high redshift
  In this paper we analyze the kinematics, chemistry, and physical properties
of a sample of the most metal-poor damped Lyman-alpha systems (DLAs), to
uncover their links to modern-day galaxies. We present evidence that the DLA
population as a whole exhibits a `knee' in the relative abundances of the
alpha-capture and Fe-peak elements when the metallicity is [Fe/H] ~ -2.0,
assuming that Zn traces the build-up of Fe-peak elements. In this respect, the
chemical evolution of DLAs is clearly different from that experienced by Milky
Way halo stars, but resembles that of dwarf spheroidal galaxies in the Local
Group. We also find a close correspondence between the kinematics of Local
Group dwarf galaxies and of high redshift metal-poor DLAs, which further
strengthens this connection. On the basis of such similarities, we propose that
the most metal-poor DLAs provide us with a unique opportunity to directly study
the dwarf galaxy population more than ten billion years in the past, at a time
when many dwarf galaxies were forming the bulk of their stars. To this end, we
have measured some of the key physical properties of the DLA gas, including
their neutral gas mass, size, kinetic temperature, density, and turbulence. We
find that metal-poor DLAs contain a warm neutral medium with T_gas ~ 9600 K
predominantly held up by thermal pressure. Furthermore, all of the DLAs in our
sample exhibit a subsonic turbulent Mach number, implying that the gas
distribution is largely smooth. These results are among the first empirical
descriptions of the environments where the first few generations of stars may
have formed in the Universe.
