We discuss physical properties and the baryonic content of the Warm-hot Intergalactic Medium ( WHIM ) at low redshifts .
Cosmological simulations predict that the WHIM contains a large fraction of the baryons at z = 0 in the form of highly-ionized gas at temperatures between 10 ^ { 5 } and 10 ^ { 7 } K. Using high-resolution ultraviolet spectra obtained with the Space Telescope Imaging Spectrograph ( STIS ) and the Far Ultraviolet Spectroscopic Explorer ( FUSE ) we have studied the WHIM at low redshifts by searching for intervening O vi and thermally broadened Lyman \alpha ( BL ) absorption toward a number of quasars and active galactic nuclei ( AGNs ) .
Our measurements imply cosmological mass densities of \Omega _ { b } ( O vi ) \approx 0.0027 h _ { 75 } ^ { -1 } and \Omega _ { b } ( BL ) \approx 0.0058 h _ { 75 } ^ { -1 } .
Our results suggest that the WHIM at low z contains more baryonic mass than stars and gas in galaxies .