The enrichment of the intergalactic medium with adiabatic feedback - I. Metal cooling and metal diffusion

A study of metal enrichment of the intergalactic medium (IGM) using a series of smooth particle hydrodynamic (SPH) simulations is presented, employing models for metal cooling and the turbulent diffusion of metals and thermal energy. An adiabatic feedback mechanism was adopted where gas cooling was prevented on the time-scale of supernova bubble expansion 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 0.5, and a steady evolution of the universal neutral hydrogen fraction ( H I ) that compares reasonably well with observations. The evolution of the mass and metallicities in stars and various gas phases was investigated. At z = 0, about 40 per cent of the baryons are in the warm-hot intergalactic medium (WHIM), but most metals (80-90 per cent) are locked in stars. At higher redshifts the proportion of metals in the IGM is higher due to more efficient loss from galaxies. The results also indicate that IGM metals primarily reside in the WHIM throughout cosmic history, which differs from simulations with hydrodynamically decoupled explicit winds. The metallicity of the WHIM lies between 0.01 and 0.1 solar with a slight decrease at lower redshifts. The metallicity evolution of the gas inside galaxies is broadly consistent with observations, but the diffuse IGM is under enriched at z 2.5.