<p> A study of metal enrichment of the intergalactic medium (IGM) using a series
of smooth particle hydrodynamics (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 timescale 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 universal neutral hydrogen fraction (OHI) that compares
reasonably well with observations. The evolution of the mass and metallicities
in stars and various gas phases was investigated. At z=O, about 40% of the
baryons are in the warm-hot intergalactic medium (WHIM), but most metals
(80%-90%) 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. Metals enhance cooling which allows WHIM gas to
cool onto galaxies and increases star formation. Metal diffusion allows winds
to mix prior to escape, decreasing the IGM metal content in favour of gas
within galactic halos and star forming gas. Diffusion significantly increases
the amount of gas with low metallicities and improves the density-metallicity
relation. </p> <p> The galactic wind generation mechanism and the wind properties from
our simulations were investigated. It was found that: 1. Galactic winds are
most efficient for halos in the intermediate mass range 10^10Mo - 10^11 Mo . These winds dominate the metal ejection at all redshifts, although towards
lower redshift the contributions from larger halos become relatively more important.
At the low mass end gas is prevented from accreting onto halos and
has very low metallicities. At the high mass end, the fraction of halo baryons
escaped as winds declines along with the decline of stellar mass fraction in
these halos. The decrease in wind ejection is likely because of the decreases
in star formation activity, wind mass loading and wind escape efficiency as
the halo mass increases. 2. The adiabatic feedback can generate winds with
mass loading factors comparable to the ones used in explicit superwind models.
The mass loading factor decreases towards lower redshift, implying that
smaller halos have larger mass loading. 3. Metals located at lower density
were generated at earlier epochs from small halos, suggesting that the wind
traveling speed can affect the metal distribution in the IGM. </p> / Thesis / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/19188 |
| Date | 09 1900 |
| Creators | Shen, Sijing |
| Contributors | Wadsley, James, Physics and Astronomy |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
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