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We conduct an ultraviolet (HST and FUSE) spectroscopic survey of HI (Lyman lines) and seven metal ions (OVI, NV, CIV, CIII, SiIV, SiIII, FeIII) in the low-redshift intergalactic medium (IGM) at z<0. 4. We analyzed 650 Lya absorbers over redshift pathlength Delta z=5. 27, detecting numerous absorbers: 83 OVI systems, 39 CIII, 53 SiIII, 24 CIV, 24 NV, and so on. Our survey yields distributions in column density and estimates of the IGM baryon content and metallicities of C, N, O in the IGM. In the low-z IGM, we have accounted for ~40% of the baryons: 30% in the photoionized Lya forest and 10% in the (T=10⁵-6 K) warm-hot intergalactic medium (WHIM) traced by OVI. Statistical metallicities of C, N, O ions are consistent with the canonical (z=0) value of 10% solar, with considerable scatter. Improved statistics for weak OVI absorbers allows us to estimate OmegaWHIM/Omegab=0. 073+-0. 008 down to logNOVI=13. 4. NV absorption is well-correlated with OVI and both ions show similarly steep power-law indices dN/dz N^-beta with betaOVI betaNV 2 while betaHI=1. 7. We conclude that OVI and NV are reliable tracers of the portion of the WHIM at T=10⁵-6 K. CIV may be present in both collisional and photoionized phases; NCIV correlates poorly with both NHI and NOVI and betaHI<betaCIV<betaOVI. The ions CIII, SiIII, and SiIV are well correlated with HI and show patterns typical of photoionization. Adjacent ion stages of the same element (CIII/IV and SiIII/IV) provide useful constraints on the photoionization parameter, logU=-1. 5+-0. 5. Comparison of SiIV and CIV with high-z surveys shows a modest increase in line density, consistent with increasing IGM metallicity at recent epochs.
Danforth et al. (Tue,) studied this question.