THE END OF HELIUM REIONIZATION AT z {approx_equal} 2.7 INFERRED FROM COSMIC VARIANCE IN HST/COS He II Ly{alpha} ABSORPTION SPECTRA

Journal Article · Wed Jun 01 04:00:00 EDT 2011 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/733/2/L24· OSTI ID:21562655

Worseck, Gabor; Xavier Prochaska, J ^[1]; McQuinn, Matthew ^[2]; Dall'Aglio, Aldo; Wisotzki, Lutz ^[3]; Fechner, Cora; Richter, Philipp ^[4]; Hennawi, Joseph F ^[5]; Reimers, Dieter ^[6]

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1. Department of Astronomy and Astrophysics, UCO/Lick Observatory, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States)
2. Department of Astronomy, University of California, 601 Campbell Hall, Berkeley, CA 94720 (United States)
3. Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam (Germany)
4. Institut fuer Physik und Astronomie, Universitaet Potsdam, Karl-Liebknecht-Str. 24/25, 14476 Potsdam (Germany)
5. Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, 69117 Heidelberg (Germany)
6. Hamburger Sternwarte, Universitaet Hamburg, Gojenbergsweg 112, 21029 Hamburg (Germany)

We report on the detection of strongly varying intergalactic He II absorption in HST/COS spectra of two z{sub em} {approx_equal} 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 <{tau}{sub eff},He{sub ii}>{approx_equal}1 at z {approx_equal} 2.3 to <{tau}{sub eff},He{sub ii}>{approx}>5 at z {approx_equal} 3.2, but with a large scatter of 2{approx}<{tau}{sub eff},He{sub ii}{approx}<5 at 2.7 < z < 3 on scales of {approx}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 {approx}> 2.7, probably indicating He II reionization was incomplete at z{sub reion} {approx}> 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{sub reion} {approx_equal} 2.7 or even below, as suggested by a large {tau}{sub eff},He{sub ii}{approx}>3 in two of our five sightlines at z < 2.8. By doubling the sample size at 2.7 {approx}< z {approx}< 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.

• OSTI ID: 21562655
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 2 Vol. 733; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABSORPTION SPECTRA
COMPUTERIZED SIMULATION
COSMIC RADIO SOURCES
ELEMENTS
FLUIDS
GASES
HELIUM
IONIZATION
NONMETALS
QUASARS
RARE GASES
SIMULATION
SPECTRA
THREE-DIMENSIONAL CALCULATIONS