Chemical enrichment of the intracluster and intergalactic medium in a hierarchical galaxy formation model

We use a combination of high resolution N–body simulations and semi–analytic techniques to follow the formation, the evolution and the chemical enrichment of cluster galaxies in a ΛCDM Universe. We model the transport of metals between the stars, the cold gas in galaxies, the hot gas in dark matter haloes, and the intergalactic gas outside virialized haloes. We have compared three different feedback schemes. The ‘retention’ model assumes that material reheated by supernova explosions is able to leave the galaxy, but not the dark matter halo. The ‘ejection’ model assumes that this material leaves the halo and is then re–incorporated when structure collapses on larger scales. The ‘wind’ model uses prescriptions that are motivated by observations of local starburst galaxies. We require that our models reproduce the cluster galaxy luminosity function measured from the 2dF survey, the relations between stellar mass, gas mass and metallicity inferred from new SDSS data, and the observed amount of metals in the ICM. With suitable adjustment of the free parameters in the model, a reasonable fit to the observational results at redshift zero can be obtained for all three feedback schemes. All three predict that the chemical enrichment of the ICM occurs at high redshift: 70–85 per cent of the metals currently in the ICM were ejected at redshifts larger than 1, 40–60 per cent at redshifts larger than 2 and 20–45 per cent at redshifts larger than 3. Massive galaxies are important contributors to the chemical pollution: 66–76 per cent of the metals today present in the ICM were ejected by galaxies with baryonic masses larger than 10 h M⊙. The observed decline in baryon fraction from rich clusters to galaxy groups is reproduced only in an ‘extreme’ ejection scheme, where material ejected from dark matter haloes is re–incorporated on a timescale comparable to the age of the Universe. Finally, we explore how the metal abundance in the intergalactic medium as a function of redshift can constraint how and when galaxies ejected their metals.