The properties of low redshift intergalactic O VI absorbers determined from high S/N observations of 14 QSOs with the cosmic origins spectrograph

Abstract

We report on the observed properties of the plasma revealed through high signal-to-noise observations of 54 intervening O VI absorption systems containing 85 O VI and 133 H I components in a blind survey of 14 QSOs observed at ∼18 km s-1 resolution with the Cosmic Origins Spectrograph over a redshift path of 3.52 at z < 0.5. Simple systems with one or two H I components and one O VI component comprise 50% of the systems. For a sample of 45 well-aligned absorption components where the temperature can be estimated, we find evidence for cool photoionized gas in 31 (69%) and warm gas (6 > log T > 5) in 14 (31%) of the components. The total hydrogen content of the 14 warm components can be estimated from the temperature and the measured value of log N(H I). The very large implied values of log N(H) range from 18.38 to 20.38 with a median of 19.35. The metallicity, [O/H], in the 6 warm components with log T > 5.45 ranges from-1.93 to 0.03 with a median value of-1.0 dex. Ground-based galaxy redshift studies reveal that most of the absorbers we detect sample gas in the intergalactic medium extending 200 to 600 kpc beyond the closest associated galaxy. For the warm aligned O VI absorbers, we estimate Ωb(O VI)Warm = 0.0019 ± 0.0005 which corresponds to (4.1 ± 1.1)% of the baryons at low z. The warm plasma traced by the aligned O VI and H I absorption contains nearly as many baryons as are found in galaxies. © 2014. The American Astronomical Society. All rights reserved.