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Unformatted text preview: forests (Tripp, Savage, and Jenkins 2000 ApJL 534, L1), a major target of this year's FUSE observations. The ionization balance is so poorly constrained that estimates of the metallicity are extremely crude. X-ray absorption measurements of O VI-O VIII work on a few lines of sight, and suggest that the hot and hotter phases of the IGM are major reservoirs of baryons. In fact, more properly, the major reservoirs of baryons. The following table lists some recent consensus values (courtesy of G. Bothun) on the fractions of critical density contributed by various kinds of (normal) matter. Phase Density fraction All baryons 0.041 Galaxies 0.003 0.001 H I 0.00039-0.00063 Lyman forest 0.008-0.012 O VI medium 0.003-0.008 The enrichment of the IGM may go beyond supernova ejecta leaking from galaxies and clusters, back to the first generation of massive stars before galaxy formation proper occurred....
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- Fall '10