Observations of Intergalactic Heavy-Element Enrichment in the Early Universe

Citation

Simcoe, Robert Andrew (2004) Observations of Intergalactic Heavy-Element Enrichment in the Early Universe. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/E1N9-BF97. https://resolver.caltech.edu/CaltechETD:etd-05082004-134233

Abstract

We present the results of a search for OVI absorption in the intergalactic medium (IGM) at 2 ≾ z ≾ 3. The measurements are taken from a set of 7 quasars observed with Keck I/HIRES. We find two classes of OVI system in the high redshift IGM. The first class is more rare (2-4 per sightline) and also quite strong (N_H1≥10^15.2). These systems resemble hot, collisionally ionized gas at high densities, and contain complex mixtures of HI and metals at a range of temperatures. Although we cannot measure the metallicities of individual strong absorbers, we estimate that the total population is enriched over 10 times above the level of the general IGM. We propose that the strong systems represent either accretion-shocked gas falling onto primitive large-scale structure, or (more likely) the remnants of high redshift galactic winds mixing into the IGM.

The second class of OVI absorber is much weaker, arising in low-density gas that is photoionized by metagalactic UV/X-ray radiation. We measure the metal content of these systems, down to densities of ρ/ρ̅ ≥ 1.6 relative to the cosmic mean. This corresponds to the filaments of the cosmic web, which contain over half of the baryons in the high redshift universe. We develop a new method to calculate the metallicity distribution function of the Ly-α forest using survival statistics. Carbon and oxygen are both distributed lognormally, with mean〈[O/H]〉≈ -2.85 and scatter of σ = 0.75 dex. We observe no decline in metallicity toward lower densities, indicating that metals are mixed very efficiently within the filaments. Comparison with Population III and galactic wind enrichment models suggests that the enrichment was dominated by superwinds. We estimate that roughly half of all baryons in the IGM came into contact with metal-rich winds by z ~ 2.5. Using a "closed box" model of intergalactic enrichment, we estimate that early galaxies typically recycled 0.1-0.4% of their mass back into the IGM as heavy elements prior to this epoch.

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