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| Paper: |
Missing Baryons in the Warm-Hot Intergalactic Medium |
| Volume: |
348, Astrophysics in the Far Ultraviolet: Five Years of Discovery with FUSE |
| Page: |
341 |
| Authors: |
Tripp, T.M.; Bowen, D.V.; Sembach, K.R.; Jenkins, E.B.; Savage, B.D.; Richter, P. |
| Abstract: |
This review briefly discusses the use of UV absorption lines in the spectra of low-redshift QSOs for the study of the physical conditions, metallicity, and baryonic content of the low–z IGM, with emphasis on implications for the missing baryons problem. Current results on the statistics and baryonic content of intervening, low–z O VI and Lyα absorption-line systems are presented with some comments on overlap between these two classes of absorbers and consequent baryon double-counting problems. From observations of a sample of 16 QSOs observed with the E140M echelle mode of STIS, we find 44 intervening O VI absorbers and 14 associated O VI systems (i.e, systems with zabs ≈ zQSO). This sample implies that the number of intervening O VI absorbers per unit redshift is dN/dz(O VI) = 23 ± 4 for lines with rest equivalent width > 30 mÅ. The intervening O VI systems contain at least 7% of the baryons if their typical metallicity is 1/10 solar and the O VI ion fraction is ≤0.2. This finding is consistent with predictions made by cosmological simulations of large-scale structure growth. Recently, a population of remarkably broad Lyα lines have been recognized in low–z quasar spectra. If the breadth of these Lyα features is predominantly due to thermal motions, then these H I absorbers likely harbor an important fraction of the baryons. We present and discuss some examples of the broad Lyα absorbers. Finally, we summarize some findings on the relationships between O VI absorbers and nearby galaxies/large-scale structures. |
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