Observations of intergalactic heavy-element enrichment in the early universe

Details Observations of intergalactic heavy-element enrichment in the early universe Observations of intergalactic heavy-element enrichment in the early universe

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004phdt........33s&link_type=abstract

Ph.D dissertation, 2004. 165 pages; United States -- California: California Institute of Technology; 2004. Publication Number:

Statistics

Intergalactic, Heavy-Element Enrichment, Early Universe, Lyman-Alpha, Galaxy Formation, Quasars

Scientific paper

We present the results of a search for O VI absorption in the intergalactic medium (IGM) at 2 [Special characters omitted.] z [Special characters omitted.] 3. The measurements are taken from a set of 7 quasars observed with Keck I/ HIRES. We find two classes of O VI system in the high redshift IGM. The first class is more rare (2-4 per sightline) and also quite strong ( N H I >= 10 15.2 ). These systems resemble hot, collisionally ionized gas at high densities, and contain complex mixtures of H I 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 O VI 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 r/ r [Special characters omitted.] 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-a forest using survival statistics. Carbon and oxygen are both distributed lognormally, with mean [left angle bracket][ O/H ][right angle bracket] [approximate] -2.85 and scatter of s = 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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