Cosmic Origins Spectrograph Detection of Ne VIII Tracing Warm-Hot Gas Toward PKS 0405–123

Type Journal Article
Names Anand Narayanan, Blair D. Savage, Bart P. Wakker, Charles W. Danforth, Yangsen Yao, Brian A. Keeney, J. Michael Shull, Kenneth R. Sembach, Cynthia S. Froning, James C. Green
Publication The Astrophysical Journal
Volume 730
Issue 1
Pages 15
Date March 1, 2011
Library Catalog NASA ADS
Abstract We report on the detection of Ne VIII in the Hubble Space Telescope/Cosmic Origins Spectrograph (COS) spectrum of the intervening absorption system at z = 0.495096 toward PKS 0405–123 (z em = 0.5726). The high signal-to-noise COS spectrum also covers absorption from H I, C III, O III, O IV, and O VI associated with this multiphase system. The Ne VIII is detected with high significance in both lines of the doublet, with integrated column densities of log Na (Ne VIII 770) = 13.96 ± 0.06 and log Na (Ne VIII 780) = 14.08 ± 0.07. We find the origin of Ne VIII consistent with collisionally ionized gas at T ~ 5 × 105 K with a large baryonic column density of N(H) ~ 1019-1020 cm–2. The metallicity in the Ne VIII gas phase is estimated to be [Ne/H] ~–0.6 ± 0.3 dex. The intermediate ions such as C III, O III, O IV, and H I are consistent with photoionization in lower ionization gas at T ~ 104 K. The O V and O VI in this absorber can have contributions from both the photoionized and collisionally ionized gas phases. The absorber is at |Δv| = 180 km s–1 systematic velocity and ρ = 110h –1 70 kpc projected separation from an MR = –19.6 galaxy of extended morphology. The collisionally ionized gas at T ~ 5 × 105 K detected in Ne VIII and O VI points to an origin in multiphase gas embedded in the hot halo of the galaxy, or in a nearby WHIM structure. The high-sensitivity UV spectroscopy afforded by COS has opened up new opportunities for discovering large reservoirs of missing baryons in the low-z universe through the detection of Ne VIII systems. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 05-26555, and the NASA-CNES/ESA Far-Ultraviolet Spectroscopic Explorer mission, operated by the Johns Hopkins University, supported by NASA contract NAS 05-32985.
Tags Galaxies: Halos, intergalactic medium, quasars: absorption lines, quasars: individual: PKS 0405–123, ultraviolet: general
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