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Resolving the Structure of Ionized Helium in the Intergalactic Medium with the Far Ultraviolet Spectroscopic ExplorerThe neutral hydrogen and the ionized helium absorption in the spectra of high-redshift quasi-stellar objects (QSOs) are unique probes of structure in the universe at epochs intermediate between the earliest density fluctuations seen in the cosmic background radiation and the distribution of galaxies visible today. We present Far-Ultraviolet Spectroscopic Explorer (FUSE) observations of the line of sight to the QSO HE2347-4342 in the 1000-1187 angstrom band at a resolving power of 15,000. Above redshift z = 2.7, the IGM is largely opaque in He II Ly-alpha (304 angstroms). At lower redshifts, the optical depth gradually decreases to a mean value tau = 1 at z = 2.4. We resolve the He II Ly-alpha absorption as a discrete forest of absorption lines in the z = 2.3 - 2.7 redshift range. Approximately 50% of these spectral features have H I counterparts with column densities N(sub HI) > 10(exp 12.3)/sq cm visible in a Keck spectrum. These account for most of the observed opacity in He II Ly-alpha. The remainder have N(sub HI) < 10(exp 12.3)/sq cm, below the threshold for current observations. A short extrapolation of the power-law distribution of H I column densities to lower values can account for these new absorbers. The He II to H I column density ratio eta averages approximately 80, consistent with photoionization of the IGM by a hard ionizing spectrum resulting from the integrated light of quasars at high redshift, but there is considerable scatter. Values of eta > 100 in many locations indicate that there may be localized contributions from starbursts or heavily filtered QSO radiation.
Document ID
20010072022
Acquisition Source
Goddard Space Flight Center
Document Type
Other
Authors
Kriss, G. A. (Space Telescope Science Inst. Baltimore, MD United States)
Shull, J. M. (Colorado Univ. Boulder, CO United States)
Oegerle, W. (NASA Goddard Space Flight Center Greenbelt, MD United States)
Zheng, W. (Johns Hopkins Univ. Baltimore, MD United States)
Davidsen, A. F. (Johns Hopkins Univ. Baltimore, MD United States)
Songaila, A. (Hawaii Univ. Honolulu, HI United States)
Tumlinson, J. (Colorado Univ. Boulder, CO United States)
Cowie, L. L. (Hawaii Univ. Honolulu, HI United States)
Dehavreng, J.-M. (Laboratoire d'Astronomie Spatiale Marseille, France)
Friedman, S. D. (Johns Hopkins Univ. Baltimore, MD United States)
Date Acquired
September 7, 2013
Publication Date
May 18, 2001
Subject Category
Astrophysics
Funding Number(s)
CONTRACT_GRANT: NAS5-32985
CONTRACT_GRANT: NAG5-7262
CONTRACT_GRANT: NAS5-26555
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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