2008ApJ...679..194D

We conduct an ultraviolet (HST and FUSE) spectroscopic survey of H I (Lyman lines) and seven metal ions (O VI, N V, C IV, C III, Si IV, Si III, Fe III) in the low-redshift IGM at z<0.4. We analyzed 650 Lyα absorbers over redshift path length Δz=5.27, detecting numerous absorbers: 83 O VI systems, 39 C III, 53 Si III, 24 C IV, 24 N V, and so on. In the low-z IGM, we have accounted for ∼40% of the baryons: 30% in the photoionized Lyα forest and 10% in the (T=10⁵-10⁶) WHIM traced by O VI. Statistical metallicities are consistent with the canonical value of 10% solar, with considerable scatter. Improved statistics for weak absorbers allows us to estimate Ω_WHIM/Ω_b=0.073±0.008 down to logN_OVI_=13.4 and 0.086±0.008 down to logN_OVI_=13.0. The O VI absorber line frequency, dN/dz=40⁺¹⁴_–8, down to 10 mÅ equivalent width suggests a 250-300 kpc extent of metals around dwarf galaxies. Many absorbers appear to contain multiphase gas, with both collisional ionization and photoionization determining the ionization state. N V absorption is well correlated with O VI, and both ions show similarly steep power-law indices dN/dz∝N^–β with β_OVI_~βNV_~2 while β_HI_=1.7. We conclude that O VI and N V are reliable tracers of the portion of the WHIM at T~10⁵-10⁶ K. C IV may be present in both collisional and photoionized phases; N_CIV_ correlates poorly with both N_HI_ and N_OVI_and β_HI_<βCIV_<βOVI_. The ions C III, Si III, and Si IV are well correlated with H I and show patterns typical of photoionization. Adjacent ion stages of the same element (C III/IV and Si III/IV) provide useful constraints on the photoionization parameter, logU~-1.5±0.5.