Journal Article

Detection of extended He <span class="smallCaps">ii</span> reionization in the temperature evolution of the intergalactic medium*

George D. Becker, James S. Bolton, Martin G. Haehnelt and Wallace L. W. Sargent

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 410, issue 2, pages 1096-1112
Published in print January 2011 | ISSN: 0035-8711
Published online December 2010 | e-ISSN: 1365-2966 | DOI:
Detection of extended He ii reionization in the temperature evolution of the intergalactic medium*

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We present new measurements of the temperature of the intergalactic medium (IGM) derived from the Lyα forest over 2.0 ≤z≤ 4.8. The small-scale structure in the forest of 61 high-resolution quasi-stellar object spectra is quantified using a new statistic, the curvature, and the conversion to temperature calibrated using a suite of hydrodynamic simulations. At each redshift, we focus on obtaining the temperature at an optimal overdensity probed by the Lyα forest, , where the temperature is nearly a one-to-one function of the curvature regardless of the slope of the temperature–density relation. The median 2σ statistical uncertainty in these measurements is 8 per cent, though there may be comparable systematic errors due to the unknown amount of Jeans smoothing in the IGM. We use our results to infer the temperature at the mean density, T0. Even for a maximally steep temperature–density relation, T0 must increase from ∼8000 K at z≃ 4.4 to ≳12 000 K at z≃ 2.8. This increase is not consistent with the monotonic decline in T0 expected in the absence of He ii reionization. We therefore interpret the observed rise in temperature as evidence of He ii reionization beginning at z≳ 4.4. The evolution of T0 is consistent with an end to He ii reionization at z∼ 3, as suggested by opacity measurements of the He ii Lyα forest, although the redshift at which T0 peaks will depend somewhat on the evolution of the temperature–density relation. These new temperature measurements suggest that the heat input due to the reionization of He ii dominates the thermal balance of the IGM over an extended period with Δz≳ 1.

Keywords: intergalactic medium; quasars: absorption lines; cosmology: observations; dark ages, reionization, first stars; early Universe

Journal Article.  13228 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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