2001/10/31 by Tom Theuns, Saleem Zaroubi, Tae-Sun Kim +5 · 5 citations
Environmental Science · Physics and Astronomy · #Adiabatic process #Amplitude #Astronomy #Astrophysics #Galaxies: Formation, Evolution, Phenomena #Galaxy #Physics #Plant Water Relations and Carbon Dynamics #QSOS #Quantum mechanics #Quasar #Redshift #Reionization #Spectral line #Stellar, planetary, and galactic studies #Universe #astro-ph
paper · pdf · doi:10.1046/j.1365-8711.2002.05316.x
published as Mon.Not.Roy.Astron.Soc. 332 (2002) 367-382 · 17 pages, minor changes, MNRAS published version
arxiv created 2002/01/30 · openalex publication_date 2002/05/01 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
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.