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arxiv: astro-ph/9912432 · v2 · submitted 1999-12-20 · 🌌 astro-ph

The thermal history of the intergalactic medium

classification 🌌 astro-ph
keywords densityintergalacticmediumcolumncut-offhighlyman-alpharedshift
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At redshifts z >~ 2, most of the baryons reside in the smooth intergalactic medium which is responsible for the low column density Lyman-alpha forest. This photoheated gas follows a tight temperature-density relation which introduces a cut-off in the distribution of widths of the Lyman-alpha absorption lines (b-parameters) as a function of column density. We have measured this cut-off in a sample of nine high resolution, high signal-to-noise quasar spectra, and determined the thermal evolution of the intergalactic medium in the redshift range 2.0-4.5. At redshift z ~ 3, the temperature at the mean density shows a peak and the gas becomes nearly isothermal. We interpret this as evidence for the reionization of HeII.

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