The metallicity distribution of HI systems in the EAGLE cosmological
  simulation
  The metallicity of strong HI systems, spanning from damped Lyman-alpha
absorbers (DLAs) to Lyman-limit systems (LLSs) is explored between z = 5->0
using the EAGLE high-resolution cosmological hydrodynamic simulation of galaxy
formation. The metallicities of LLSs and DLAs steadily increase with time in
agreement with observations. DLAs are more metal rich than LLSs, although the
metallicities in the LLS column density range (NHI = 10^17 -10^20 cm^-2) are
relatively flat, evolving from a median HI-weighted metallicity of Z<10^-2 Zsol
at z = 3 to ~10^-0.5 Zsol by z = 0. The metal content of HI systems tracks the
increasing stellar content of the Universe, holding ~5% of the integrated total
metals released from stars at z = 0. We also consider partial LLS (pLLS, NHI =
10^16-10^17 cm^-2) metallicities, and find good agreement with Wotta et al.
(2016) for the fraction of systems above (37%) and below (63%) 0.1 Zsol. We
also find a large dispersion of pLLS metallicities, although we do not
reproduce the observed metallicity bimodality and instead we make the
prediction that a larger sample will yield more pLLSs around 0.1 Zsol. We
under-predict the median metallicity of strong LLSs, and predict a population
of Z < 10^-3 Zsol DLAs at z > 3 that are not observed, which may indicate more
widespread early enrichment in the real Universe compared to EAGLE.
