He II Ly{beta} GUNN-PETERSON ABSORPTION: NEW HST OBSERVATIONS AND THEORETICAL EXPECTATIONS

Journal Article · Thu Dec 01 00:00:00 EST 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/742/2/99· OSTI ID:22004621

Syphers, David; Pieri, Matthew; Shull, J Michael ^[1]; Anderson, Scott F ^[2]; Zheng, Wei; Kriss, Gerard A ^[3]; Smith, Britton ^[4]; Meiksin, Avery ^[5]; Schneider, Donald P ^[6]

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1. CASA, Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309 (United States)
2. Astronomy Department, University of Washington, Seattle, WA 98195 (United States)
3. Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States)
4. Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States)
5. Scottish Universities Physics Alliance (SUPA), Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ (United Kingdom)
6. Department of Physics and Astronomy, Pennsylvania State University, University Park, PA 16802 (United States)

Observations of He II Ly{alpha} Gunn-Peterson troughs have proved to be a valuable probe of the epoch of helium reionization at z {approx} 3. Since this optical depth can become unmeasurably large even for modest He II fractions, various alternate techniques have been proposed to push to higher redshift, and among the more promising is looking at higher-order Lyman-series troughs. We here report four new observations of the He II Ly{beta} trough, including new data on the only sightline with a prior Ly{beta} observation. However, the effective optical depth ratio {tau}{sub eff,{beta}}/{tau}{sub eff,{alpha}} is not simply predicted by f{sub {beta}}{lambda}{sub {beta}}/f{sub {alpha}}{lambda}{sub {alpha}} = 0.16, and we analyze cosmological simulations to find that the correct ratio for helium at z {approx} 3 is {approx_equal}0.35. In one case we infer {tau}{sub eff,{alpha}} > 8.8, strong evidence that helium was not fully reionized at z = 3.2-3.5, in agreement with previous measurements suggesting a later completion of reionization.

• OSTI ID: 22004621
• Journal Information: Astrophysical Journal, Vol. 742, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ABSORPTION
COMPUTERIZED SIMULATION
COSMOLOGICAL MODELS
GALAXIES
HELIUM
LYMAN LINES
QUASARS
RED SHIFT
ULTRAVIOLET RADIATION