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Title:
Intergalactic HeII absorption towards QSO 1157+3143
Authors:
Reimers, D.; Fechner, C.; Hagen, H.-J.; Jakobsen, P.; Tytler, D.; Kirkman, D.
Affiliation:
AA(Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany ), AB(Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany), AC(Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany), AD(Astrophysics Missions Division, RSSD, European Space Agency, ESTEC, 2200 AG Noordwijk, The Netherlands), AE(Center for Astrophysics and Space Sciences, University of California, San Diego, MS 0424, La Jolla, CA 92093-0424, USA), AF(Center for Astrophysics and Space Sciences, University of California, San Diego, MS 0424, La Jolla, CA 92093-0424, USA)
Publication:
Astronomy and Astrophysics, Volume 442, Issue 1, October IV 2005, pp.63-68 (A&A Homepage)
Publication Date:
10/2005
Origin:
EDP Sciences
Keywords:
galaxies: quasars: individual: QSO 1157+3143, galaxies: quasars: absorption lines, cosmology: observations
DOI:
10.1051/0004-6361:20053365
Bibliographic Code:
2005A&A...442...63R

Abstract

We report the discovery of a further line of sight allowing detection of He II Lyα absorption by the intergalactic medium. A HST/STIS survey of 32 bright z ˜ 3 quasars selected from the Hamburg Quasar Surveys yielded one detection toward QSO 1157+3143 (z ˜ 3, B ≃ 17). A 10 orbit follow-up spectrum reveals a UV spectrum significantly suppressed by two intervening Lyman limit systems at z=2.77 and 2.94, but with the continuum flux recovering sufficiently shortward of ~1700 Å to allow study of the He II absorption spectrum in the redshift range 2.75 ≤ z ≤ 2.97. The absorption is characterized by alternating voids and dense filament structures seen in both He II and H I. Attempts to model the He II opacity in terms of H I Lyα forest absorption are not successful in the voids, suggesting that He II reionization is not complete between z=2.77 and 2.97 or that an optically thin Lyman limit system with z ≈ 0.3 is responsible for the additional opacity.
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