Most of our detailed information about IGM physics comes from QSO absorption spectra at 2.5 < z < 3.5, where bright background sources are relatively abundant and optical spectrographs are fast. This contribution describes newer measurements made with high-quality Magellan and Gemini spectra of the z > 4 IGM, and compares these with the existing body of work at lower redshift. Fairly detailed measurements of chemical abundance evolution can be made at
intermediate redshifts (with associated implications for galaxy feedback), and there is some tentative indication of IGM enrichment as high as z ~ 6.
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