Talk Details

Wednesday, November 25, 2009 - 3:15pm

Sijing Shen (McMaster):

"IGM Enrichment with Adiabatic Feedback, Metal Cooling and Turbulent Diffusion"

Abstract. We present a study of the metal enrichment of the intergalactic medium (IGM) using a series of smooth particle hydrodynamic (SPH) simulations. We employ models for metal cooling and turbulent diffusion of metals and thermal energy. The star formation and adiabatic feedback model naturally drives winds and reproduces the observed cosmic star formation history (SFH) while preserving the universal neutral hydrogen fraction. At z =0, about 40% of the baryons are in the warm-hot intergalactic medium (WHIM), but most metals (82%) are locked in stars. At higher redshift metals are mostly in the IGM due to more efficient loss from galaxies. Our results indicate that IGM metals primarily reside in the WHIM throughout cosmic history (differing from the momentum driven wind model). The metallicity of the WHIM lies between 0.01 and 0.1 solar with a slight decrease at lower redshift. The metallicity evolution of the IGM and the gas inside galaxies are broadly consistent with observations. We characterized the wind efficiency in our model. Galactic winds are most efficient for galaxies in intermediate mass range 10^10-10^11.5 solar masses. For galaxies with masses lower than 10^10 solar masses, the background UV radiation prevents gas from accretion, resulting low metallicities for gas both within and outside these galaxies. The efficiency of star formation increases for galaxies above 10^10 solar masses, which increases the metal content of the galactic winds. Beyond 10^11.5 solar masses the star formation declines following the classic Rees and Ostriker (1977) picture and the metal content of the objects and winds saturates. Metal cooling transfers metals from the WHIM to bound gas, and increases the SFR. Metal diffusion allows winds to mix prior to escape, thus decreasing the IGM metal content in favour of gas within galactic halos and star forming gas. Diffusion significantly increases the amount of low metallicity gas and affects the density-metallicity relation.