| Metals are produced in the stars in the galaxies, and a variety of feedback processes move metals from the sites of production into the intergalactic medium (IGM), enriching the material for future generations of stars. The signature of this process is etched in the recycled gas: its metallicity, elemental abundances, density, distribution, etc. The study of the low-redshift, z <, IGM is the study of the last eight-billion years of cosmic chemical evolution and all prior enrichment.;In this thesis, I characterize the cosmic enrichment cycle with the use of observations and simulations. The gas is observed through quasar absorption-line spectroscopy. As the light of a distant quasar travels to us, intervening clouds of gas absorb the light at wavelengths characteristic, albeit redshifted, of the elements in the clouds. By identifying and modeling the elements associated with the absorption systems, I learn the ionic composition and density of the cosmic web (voids, filaments, and/or groups) along the line of sight.;From a detailed study of a single sightline, I observe a multi-phase IGM, with kinematically-distinct, hot and warm components (T ≈ 105.5 K and 104 K, respectively). By correlating the absorption systems with a complementary galaxy survey of the field around the background quasar, I find that the IGM systems arise in a variety of galactic environments. The metal-lines systems all have L > 0.1 L* galaxies within a few hundred kiloparsecs, which suggests this is the distance to which galactic feedback processes typically disperse metals.;I conduct a large, blind survey for triply-ionized carbon (C IV) absorption at z < 1 in the spectra of 49 low-redshift quasars and compare their properties with those detected at z > 1. The mass density in C IV doublets with 13 ≤ log N(C+3) ≤ 15 at z < 1 has increased by a factor of 2.8 +/- 0.7 over the error-weighted mean of the 1.5 < z < 5 measurements, where the mass density has not evolved significantly. The line density d NCIV /dX has not evolved as much, indicating that the average column density per doublet increases with decreasing redshift.;In addition, I compare the observed properties of C IV absorbers with those predicted by cosmological hydrodynamic simulations with a variety of physical models (e.g., feedback, cosmology). I also use the results from the simulations that reproduce well the observations to understand better the physical conditions giving rise to the C IV absorbing gas. The observations and simulations indicate that the log N(C+3) > 13 C IV absorption systems predominately come from circum-galactic (or halo) gas. |
