2005/03/02 by Blair D. Savage, Nicolas Lehner, Bart P. Wakker +2 · 10 citations
Chemistry · Physics and Astronomy · #Absorption (acoustics) #Absorption spectroscopy #Analytical Chemistry (journal) #Astrophysics #Astrophysics and Star Formation Studies #Atomic physics #Chemistry #Galaxies: Formation, Evolution, Phenomena #Galaxy #Intergalactic travel #Line (geometry) #Optics #Physics #Quasar #Redshift #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/429985
published as Astrophys.J. 626 (2005) 776-794 · 32 pages text and 9 pages of figures. Accepted by the Astrophysical Journal
arxiv created 2005/03/02 · openalex publication_date 2005/06/15 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
High-resolution FUSE and STIS observations of the bright QSO HE 0226-4110 ( z em = 0.495) reveal the presence of a multiphase absorption-line system at z abs (O ) = 0.20701 containing absorption from H I (Lyα to Lyθ), C III, O III, O IV, O VI, N III, Ne VIII, Si III, S VI, and possibly S V. Single-component fits to the Ne VIII and O VI absorption doublets yield log N (Ne ) = 13.89 ± 0.11, b = 23 ± 15 km s -1 , and v = -7 ± 6 km s -1 and log N (O ) = 14.37 ± 0.03, b = 31 ± 2 km s -1 , and v = 0 ± 2 km s -1 . The Ne VIII and O VI doublets are detected at 3.9 and 16 σ significance levels, respectively. This represents the first detection of intergalactic Ne VIII, a diagnostic of gas with temperature in the range from ~5 × 10 5 to ~1 × 10 6 K. Through the entire absorber, N (Ne )/ N (O ) = 0.33 ± 0.10. The O VI and Ne VIII are not likely to have been created in a low-density medium photoionized solely by the extragalactic background at z = 0.2, since the required path length ~11 Mpc (assuming [ Z /H] = -0.5) implies that the Hubble flow absorption-line broadening would be ~10 times greater than the observed line widths. A collisional ionization origin is therefore more likely. Assuming [Ne/H] and [O/H] = -0.5, the value N (Ne )/ N (O ) = 0.33 ± 0.10 is consistent with gas in collisional ionization equilibrium near T = 5.4 × 10 5 K with log N (H) = 19.9 and N (H)/ N (H ) = 1.7 × 10 6 . Various nonequilibrium ionization processes are also considered, because gas with T ~ (1-6) × 10 5 K cools efficiently. The observations of O VI and Ne VIII in the z = 0.20701 system support the basic idea that a substantial fraction of the baryonic matter at low redshift exists in hot, very highly ionized gaseous structures. Absorption by the moderately ionized gas (including O IV and S VI) is well modeled by gas in photoionization equilibrium with [ Z /H] = -0.5 ± 0.2, log U ~ -1.85, T ~ 2.1 × 10 4 K, n H ~ 2.6 × 10 -5 cm -3 , P / k ~ 0.5 cm -3 K, and a path length of ~60 kpc. These values suggest that the moderately ionized absorber may be associated with the modestly enriched photoionized gas in a galaxy group or the outermost regions of a galaxy halo.