The Enrichment of the Intergalactic Medium with Adiabatic Feedback I:
  Metal Cooling and Metal Diffusion
  A study of the IGM metal enrichment using a series of SPH simulations is
presented, employing metal cooling and turbulent diffusion of metals and
thermal energy. An adiabatic feedback mechanism was adopted where gas cooling
was prevented to generate galactic winds without explicit wind particles. The
simulations produced a cosmic star formation history (SFH) that is broadly
consistent with observations until z $\sim$ 0.5, and a steady evolution of the
universal neutral hydrogen fraction ($\Omega_{\rm H I}$). At z=0, about 40% of
the baryons are in the warm-hot intergalactic medium (WHIM), but most metals
(80%-90%) are locked in stars. At higher z the proportion of metals in the IGM
is higher due to more efficient loss from galaxies. The IGM metals primarily
reside in the WHIM throughout cosmic history. The metallicity evolution of the
gas inside galaxies is broadly consistent with observations, but the diffuse
IGM is under enriched at z $\sim$ 2.5. Galactic winds most efficiently enrich
the IGM for halos in the intermediate mass range $10^{10}$M$_{\sun}$ -
$10^{11}$ M$_{\sun}$. At the low mass end gas is prevented from accreting onto
halos and has very low metallicities. At the high mass end, the fraction of
halo baryons escaped as winds declines along with the decline of stellar mass
fraction of the galaxies. This is likely because of the decrease in star
formation activity and in wind escape efficiency. Metals enhance cooling which
allows WHIM gas to cool onto galaxies and increases star formation. Metal
diffusion allows winds to mix prior to escape, decreasing the IGM metal content
in favour of gas within galactic halos and star forming gas. Diffusion
significantly increases the amount of gas with low metallicities and changes
the density-metallicity relation.
