The enrichment history of cosmic metals
  We use a suite of cosmological, hydrodynamical simulations to investigate the
chemical enrichment history of the Universe. Specifically, we trace the origin
of the metals back in time to investigate when various gas phases were enriched
and by what halo masses. We find that the age of the metals decreases strongly
with the density of the gas in which they end up. At least half of the metals
that reside in the diffuse intergalactic medium (IGM) at redshift zero (two)
were ejected from galaxies above redshift two (three). The mass of the haloes
that last contained the metals increases rapidly with the gas density. More
than half of the mass in intergalactic metals was ejected by haloes with total
masses less than 1e11 solar masses and stellar masses less than 1e9 solar
masses. The range of halo masses that contributes to the enrichment is wider
for the hotter part of the IGM. By combining the `when' and `by what' aspects
of the enrichment history, we show that metals residing in lower density gas
were typically ejected earlier and by lower mass haloes.
