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T. M. Tripp (University of Massachusetts)
Hydrodynamic simulations of the growth of large-scale structures predict that at the present epoch, 30-50% of the baryons in the universe are located in shock-heated intergalactic gas at 105 - 107 K, the ``warm-hot intergalactic medium" (WHIGM). A variety of methods can be used to search for this shocked gas. For example, gas in this temperature range should emit soft X-rays. However, since the gas is also predicted to have rather low density, it is quite challenging to detect in emission, and compelling detections of these baryons in emission have not yet emerged. Studies of absorption lines in the spectra of background quasars provide a much more sensitive probe of low-density gas, and absorption lines hold the greatest promise for revealing this baryon reservoir. This talk will review results from absorption-line studies of highly ionized intergalactic gas at low redshifts. The talk will begin with observations of gas in the immediate vicinity of the Milky Way, with emphasis on the high-velocity clouds, and then turn to observations of progressively more distant absorption-line systems. Comments will be made on the physical conditions, baryonic content, and metal enrichment of the low-z IGM and the relationships between QSO absorption-line systems and galaxies/large-scale structures.
This research is supported by the NASA LTSA grant NAG5-11136.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.