O VI Absorbers Tracing Hot Gas Associated with a Pair of Galaxies at z = 0.167

Type Journal Article
Names B. D. Savage, A. Narayanan, B. P. Wakker, J. T. Stocke, B. A. Keeney, J. M. Shull, K. R. Sembach, Y. Yao, J. C. Green
Publication The Astrophysical Journal
Volume 719
Issue 2
Pages 1526-1545
Date August 1, 2010
URL http://adsabs.harvard.edu/abs/2010ApJ...719.1526S
Library Catalog NASA ADS
Abstract High signal-to-noise observations of the QSO PKS 0405-123 (z em = 0.572) with the Cosmic Origins Spectrograph from 1134 to 1796 Å with a resolution of ~17 km s-1 are used to study the multi-phase partial Lyman limit system (LLS) at z = 0.16716, which has previously been studied using relatively low signal-to-noise spectra from STIS and FUSE. The LLS and an associated H I-free broad O VI absorber likely originate in the circumgalactic gas associated with a pair of galaxies at z = 0.1688 and 0.1670 with impact parameters of 116 h -1 70 and 99 h -1 70. The broad and symmetric O VI absorption is detected in the z = 0.16716 rest frame with v = -278 ± 3 km s-1, log N(O VI) = 13.90 ± 0.03, and b = 52 ± 2 km s-1. This absorber is not detected in H I or other species with the possible exception of N V. The broad, symmetric O VI profile and the absence of corresponding H I absorption indicate that the circumgalactic gas in which the collisionally ionized O VI arises is hot (log T ~ 5.8-6.2). The absorber may represent a rare but important new class of low-z intergalactic medium absorbers. The LLS has strong asymmetrical O VI absorption with log N(O VI) = 14.72 ± 0.02 spanning a velocity range from -200 to +100 km s-1. The high and low ions in the LLS have properties resembling those found for Galactic highly ionized high-velocity clouds where the O VI is likely produced in the conductive and turbulent interfaces between cool and hot gas. Based on observations obtained with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS5-26555.
Tags Galaxies: Halos, ULTRAVIOLET: GALAXIES, intergalactic medium
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