Far-Ultraviolet Spectroscopy of the Intergalactic and Interstellar Absorption toward 3C 273

We present Far Ultraviolet Spectroscopic Explorer observations of the molecular, neutral atomic, weakly ionized, and highly ionized components of the interstellar and intergalactic material toward the quasar 3C 273. We identify Lyβ absorption in eight of the known intergalactic Lyα absorbers along the sight line with rest-frame equivalent widths W_r(Lyα) ≳ 50 mÅ. Refined estimates of the H I column densities and Doppler parameters (b) of the clouds are presented. We find a range of b ≈ 16-46 km s^-1. We detect multiple H I lines (Lyβ-Lyθ) in the 1590 km s^-1 Virgo absorber and estimate log N(H ) = 15.85 ±, which is 10 times more H I than in all of the other absorbers along the sight line combined. The Doppler width of this absorber, b ≈ 16 km s^-1, implies T ≲ 15,000 K. We detect O VI absorption at 1015 km s^-1 at the 2-3 σ level that may be associated with hot, X-ray-emitting gas in the Virgo Cluster. We detect weak C III and O VI absorption in the intergalactic medium at z = 0.12007; this absorber is predominantly ionized and has N(H⁺)/N(H I) ≥ 4000Z^-1, where Z is the metallicity. Strong Galactic interstellar O VI is present between -100 and 100 km s^-1, with an additional high-velocity wing containing about 13% of the total O VI between ~100 and ~240 km s^-1. The Galactic O VI, N V, and C IV lines have similar shapes, with roughly constant ratios across the -100 to 100 km s^-1 velocity range. The high-velocity O VI wing is not detected in other species. Much of the interstellar high ion absorption probably occurs within a highly fragmented medium within the Loop IV remnant or in the outer cavity walls of the remnant. Multiple hot gas production mechanisms are required. The broad O VI absorption wing likely traces the expulsion of hot gas out of the Galactic disk into the halo. A flux limit of 5.4 × 10^-16 ergs cm^-2 s^-1 on the amount of diffuse O VI emission present ~35 off the 3C 273 sight line combined with the observed O VI column density toward 3C 273, log N(O VI) = 14.73 ± 0.04, implies n_e ≲ 0.02 cm^-3 and p/k ≲ 11,500 cm^-3 K for an assumed temperature of 3 × 10⁵ K. The elemental abundances in the neutral and weakly ionized interstellar clouds are similar to those found for other halo clouds. The warm neutral and warm ionized clouds along the sight line have similar dust-phase abundances, implying that the properties of the dust grains in the two types of clouds are similar. Interstellar H₂ absorption is present at ≈16 km s^-1 at a level of log N(H₂) ~ 15.71 but does not trace the main column density concentration along the sight line observed in H I 21 cm emission.