Abstract
Abstract We present a new investigation of the thermal history of the intergalactic medium (IGM) during and after reionization using the Lyα forest flux power spectrum at 4.0 ≲ z ≲ 5.2. Using a sample of 15 high-resolution spectra, we measure the flux power down to the smallest scales ever probed at these redshifts (−1 ≲ log(k/km−1 s) ≲ −0.7). These scales are highly sensitive to both the instantaneous temperature of the IGM and the total energy injected per unit mass during and after reionization. We measure temperatures at the mean density of T 0 ∼ 7000–8000 K, consistent with no significant temperature evolution for redshifts 4.2 ≲ z ≲ 5.0. We also present the first observational constraints on the integrated IGM thermal history, finding that the total energy input per unit mass increases from u 0 ∼ 4.6 to 7.3 eV from z ∼ 6 to 4.2 assuming a ΛCDM cosmology. We show how these results can be used simultaneously to obtain information on the timing and the sources of the reionization process. Our first proof of concept using simplistic models of instantaneous reionization produces results comparable to and consistent with the recent Planck constraints, favoring models with .
Highlights
The epoch of hydrogen reionization represents one of the most dramatic phases of evolution of the universe
While current constraints from cosmic microwave background (CMB) observations are consistent with a rapid reionization at redshift zrei ; 7.7 ± 0.7 (Planck Collaboration et al 2018), measurements of the fraction of neutral hydrogen at high redshift have been obtained from the presence of Lyα damping wings (Mortlock et al 2011; Simcoe et al 2012; Greig et al 2017; Davies et al 2018) and from the weakening of Lyα emission lines in z ∼ 6–8 galaxies (e.g., Caruana et al 2014; Schmidt et al 2016; Sadoun et al 2017; Mason et al 2018)
According to the analysis presented in N16 using mock observations with a redshift path Δz = 4, a continuum-to-noise ratio (C/N) of ∼15 per 3 km s−1 pixel is necessary to break the degeneracy between thermal broadening and pressure smoothing and measure the thermal parameters with a statistical uncertainty of ∼20%
Summary
The epoch of hydrogen reionization represents one of the most dramatic phases of evolution of the universe. During this period, the UV radiation from the first luminous sources reionized the neutral hydrogen (and He I) atoms in the diffuse intergalactic medium (IGM), driving the transition from a neutral to a highly ionized universe. The most direct probes of the highly ionized IGM have been obtained from observations of intergalactic Lyα absorption along the lines of sight to high-redshift quasars. The available data seem to generally support a late reionization scenario (with the bulk of reionization happening at z ∼ 6–8) but are still consistent with a relatively broad range of reionization histories
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