Probing the Intergalactic Medium with the O Vi Forest

Recent STIS and FUSE observations have detected O VI absorption lines at low redshift that are not clearly associated with any galactic system. In this paper, we argue that these lines are due to metal enriched hot gas in the intergalactic medium. Using numerical simulations of a cosmological-constant dominated cosmology, combined with reasonable assumptions about the metallicity distribution, we show that the number density and internal characteristics of these lines are correctly predicted. We find that the O VI is primarily produced by collisional ionization from gas at a few times 10 K for lines with equivalent widths larger than 40 mÅ, while weaker lines can also be produced by photo-ionization. The absorption occurs in diffuse gas in filaments at moderate overdensity (δ ∼ 5− 100). Subject headings: intergalactic medium — quasars: absorption lines — large-scale structure of universe — methods: numerical