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Detection of extended He II reionization in the temperature evolution of the intergalactic medium

Becker, George D. and Bolton, James S. and Haehnelt, Martin G. and Sargent, Wallace L. W. (2011) Detection of extended He II reionization in the temperature evolution of the intergalactic medium. Monthly Notices of the Royal Astronomical Society, 410 (2). pp. 1096-1112. ISSN 0035-8711.

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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, T(Δ[overbar]), 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 T(Δ[overbar]) results to infer the temperature at the mean density, T_0. Even for a maximally steep temperature–density relation, T_0 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 T_0 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 T_0 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.

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Additional Information:© 2010 The Authors. Monthly Notices of the Royal Astronomical Society © 2010 RAS. Accepted 2010 August 11. Received 2010 August 5; in original form 2010 May 21. A part of the observations were made at the W. M. Keck Observatory which is operated as a scientific partnership between the California Institute of Technology and the University of California; it was made possible by the generous support of the W. M. Keck Foundation. This paper also includes data gathered with the 6.5-m Magellan Telescopes located at Las Campanas Observatory, Chile. The authors would like to thank Bryan Penprase for reducing much of the low-redshift HIRES data, and the anonymous referee for their helpful comments.We also wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. The hydrodynamical simulations used in this work were performed using the Darwin Supercomputer of the University of Cambridge High Performance Computing Service (, provided by Dell Inc. using Strategic Research Infrastructure Funding from the Higher Education Funding Council for England. GDB acknowledges financial support from the Kavli foundation. JSB has been supported by an ARC Australian post-doctoral fellowship (DP0984947). WLWS has been supported by the National Science Foundation through grant AST-0606868.
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Kavli foundationUNSPECIFIED
ARC Australian post-doctoral fellowshipDP0984947
Subject Keywords:intergalactic medium; quasars: absorption lines; cosmology: observations; dark ages, reionization, first stars; early Universe
Issue or Number:2
Record Number:CaltechAUTHORS:20110214-104208307
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Official Citation:Becker, G. D., Bolton, J. S., Haehnelt, M. G. and Sargent, W. L. W. (2011), Detection of extended He ii reionization in the temperature evolution of the intergalactic medium. Monthly Notices of the Royal Astronomical Society, 410: 1096–1112. doi: 10.1111/j.1365-2966.2010.17507.x
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:22168
Deposited By: Jason Perez
Deposited On:15 Feb 2011 20:17
Last Modified:03 Oct 2019 02:35

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