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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 606657.0, MPI für Astronomie / Publikationen_mpia
The end of Helium reionization at z ~= 2.7 inferred from cosmic variance in HST/COS He II Lya absorption spectra
Authors:Worseck, G.; Prochaska, J. X.; McQuinn, M.; Dall'Aglio, A.; Fechner, C.; Hennawi, J. F.; Reimers, D.; Richter, P.; Wisotzki, L.
Date of Publication (YYYY-MM-DD):2011
Journal Abbrev.:The Astrophysical Journal Letters
Issue / Number:2
Audience:Not Specified
Abstract / Description:We report on the detection of strongly varying intergalactic He II absorption in HST/COS spectra of two z em ~= 3 quasars. From our homogeneous analysis of the He II absorption in these and three archival sightlines, we find a marked increase in the mean He II effective optical depth from \langle \tau _{eff,He\,\mathsc{ii}}\rangle \simeq 1 at z ~= 2.3 to \langle \tau _{eff,He\,\mathsc{ii}}\rangle \gtrsim 5 at z ~= 3.2, but with a large scatter of 2\lesssim \tau _{eff,He\,\mathsc{ii}}\lesssim 5 at 2.7 < z < 3 on scales of ~10 proper Mpc. This scatter is primarily due to fluctuations in the He II fraction and the He II-ionizing background, rather than density variations that are probed by the coeval H I forest. Semianalytic models of He II absorption require a strong decrease in the He II-ionizing background to explain the strong increase of the absorption at z >~ 2.7, probably indicating He II reionization was incomplete at z reion >~ 2.7. Likewise, recent three-dimensional numerical simulations of He II reionization qualitatively agree with the observed trend only if He II reionization completes at z reion ~= 2.7 or even below, as suggested by a large \tau _{eff,He\,\mathsc{ii}}\gtrsim 3 in two of our five sightlines at z < 2.8. By doubling the sample size at 2.7 <~ z <~ 3, our newly discovered He II sightlines for the first time probe the diversity of the second epoch of reionization when helium became fully ionized. Based on observations made 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 NAS5-26555 (programs 7575, 9350, 11528, 11742). Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and NASA; it was made possible by the generous financial support of the W.M. Keck Foundation. Based on observations collected at the European Organization for Astronomical Research in the Southern Hemisphere, Chile (programs 166.A.-0106, 071.A-0066, 083.A-0421).
Free Keywords:dark ages; reionization; first stars; diffuse radiation; intergalactic medium; quasars: absorption lines; quasars: individual: SDSS J092447.36+485242.8 SDSS J110155.74+105302.3
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
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