Astronomy and Astrophysics – Astrophysics – Cosmology and Extragalactic Astrophysics
Scientific paper
2011-08-24
Astronomy and Astrophysics
Astrophysics
Cosmology and Extragalactic Astrophysics
ApJ accepted. 25 pages, 3 figures, 4 tables
Scientific paper
Observations of He II Ly{\alpha} Gunn-Peterson troughs have proved to be a valuable probe of the epoch of helium reionization at z~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}_eff,{\beta}/{\tau}_eff,{\alpha} is not simply predicted by (f_{\beta} {\lambda}_{\beta})/(f_{\alpha} {\lambda}_{\alpha})=0.16, and we analyze cosmological simulations to find that the correct ratio for helium at z~3 is ~0.35. In one case we infer {\tau}_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.
Anderson Scott F.
Kriss Gerard Anthony
Meiksin Avery
Pieri Matthew
Schneider Donald P.
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