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

Abstract

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 galaxies in a A cold dark matter (ACDM) 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 reincorporated 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 the new Sloan Digital Sky Survey (SDSS) data, and the observed amount of metals in the intracluster medium (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: 60-80 per cent of the metals currently in the ICM were ejected at redshifts larger than 1, 35-60 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: about half of the metals present today in the ICM were ejected by galaxies with baryonic masses larger than 10 10 h -1 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 reincorporated on a time-scale comparable to the age of the Universe. Finally, we explore how the metal abundance in the intergalactic medium as a function of redshift can constrain how and when galaxies ejected their metals.