Intergalactic Baryons in the Local Universe
Charles W. Danforth (U. Colorado)

TL;DR
This paper reviews observational and theoretical evidence for the distribution of baryons in the local universe, emphasizing the role of the warm-hot intergalactic medium (WHIM) as a significant baryon reservoir.
Contribution
It argues that most OVI absorbers at low redshift are shock-heated gas in the WHIM, providing a more accurate estimate of baryons in this phase.
Findings
Warm, photoionized phase accounts for ~30% of baryons at z~0
Enriched gas at T=10^5-10^6 K can account for ~10% of baryons at z<0.5
Most OVI absorbers are likely shock-heated gas, not photoionized
Abstract
Simulations predict that shocks from large-scale structure formation and galactic winds have reduced the fraction of baryons in the warm, photoionized phase (the Lya forest) from nearly 100% in the early universe to less than 50% today. Some of the remaining baryons are predicted to lie in the warm-hot ionized medium (WHIM) phase at T=10^5-10^7 K, but the quantity remains a highly tunable parameter of the models. Modern UV spectrographs have provided unprecedented access to both the Lya forest and potential WHIM tracers at z~0, and several independent groups have constructed large catalogs of far-UV IGM absorbers along ~30 AGN sight lines. There is general agreement between the surveys that the warm, photoionized phase makes up ~30% of the baryon budget at z~0. Another ~10% can be accounted for in collapsed structures (stars, galaxies, etc.). However, interpretation of the ~100 high-ion…
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