Journal Article

Temperature fluctuations in the intergalactic medium

Tom Theuns, Saleem Zaroubi, Tae-Sun Kim, Panayiotis Tzanavaris and Robert F. Carswell

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 332, issue 2, pages 367-382
Published in print May 2002 | ISSN: 0035-8711
Published online May 2002 | e-ISSN: 1365-2966 | DOI:
Temperature fluctuations in the intergalactic medium

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The temperature of the low-density intergalactic medium (IGM) is set by the balance between adiabatic cooling resulting from the expansion of the Universe, and photoheating by the ultraviolet (UV) background. We have analysed the Lyα forest of 11 high-resolution quasar spectra using wavelets, and find strong evidence of a marked jump in the temperature at the mean density, T0, of 60±14 per cent over the redshift interval z=[3.5,3.1], which we attribute to reionization of He ii. The jump can be seen in all three of our spectra that straddle redshift 3.3, at a significance of ≥99 per cent. Below z∼3.1, our results are consistent with a smooth cooling down of the universe, as expected when adiabatic expansion dominates over photoheating by a UV background from quasi-stellar objects (QSOs) and galaxies. We find no evidence of thermal fluctuations on scales ≥5000 km s−1 larger than 50 per cent, which could be detected by our method, suggesting that the IGM follows a reasonably well-defined temperature–density relation. We demonstrate that the mean wavelet amplitude 〈A〉∝1/T0, and calibrate the relation with hydrodynamical simulations. We find T0≥1.2×104 K at z≥3.6. Such high temperatures suggest that H i reionization occurred relatively recently.

Keywords: hydrodynamics; intergalactic medium; quasars: absorption lines; cosmology: theory; large-scale structure of Universe

Journal Article.  11746 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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