Revealing Reionization with the Thermal History of the Intergalactic Medium: New Constraints from the Lyα Flux Power Spectrum

Abstract

We present a new investigation of the thermal history of the intergalactic medium (IGM) during and after reionization using the Lyman-α forest flux power spectrum at 4.0 z 5.2. Using a sample of 15 highresolution 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 eV m −1 p to 7.3 eV m −1 p from z ∼ 6 to 4.2 assuming a Λ-CDM 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 z rei ∼ 8.5 +1.1 −0.8 .

Probing the thermal state of the intergalactic medium at z > 5 with the transmission spikes in high-resolution Ly α forest spectra

“…Nasir et al 2016). For comparison, Boera et al (2019) have recently inferred u0 = 4.6 +1.4 −1.2 eV m −1 p over the redshift interval 6 < z < 13 from new measurements of the Lyα FPS at z = 5, which is consistent with our default simulation at ∼ 1.3σ. Interestingly, Fig.…”

Observing the tail of reionization: neutral islands in the z = 5.5 Lyman-α forest

“…The bottom panel of Fig. 8 compares our models of u 0 with measurements by Boera et al (2019). The post-reionization u 0 in early-reion-short-mfp is ∼ 25 % higher than in the late models owing to the earlier start of reionization.…”

“…The post-reionization u 0 in early-reion-short-mfp is ∼ 25 % higher than in the late models owing to the earlier start of reionization. Figure 9 compares our models to the z = 5 joint posterior distribution of T 0 and u 0 from Boera et al (2019). The contours correspond to 68 and 95 % credibility regions and the red, blue, and green dots correspond to the late-reion-long-mfp, early-reion-short-mfp, and late-reion-short-mfp models, respectively.…”

“…Posterior distributions for the parameters T 0 and u 0 fromBoera et al (2019), obtained from flux power spectrum measurements at z = 5. The red, blue, and green dots correspond to the late-reion-long-mfp, early-reion-short-mfp, and latereion-short-mfp models, respectively The grey contours show the 68 and 95 percent credibility regions.…”

Imprints of temperature fluctuations on the z ∼ 5 Lyman-α forest: a view from radiation-hydrodynamic simulations of reionization

“…This value of F also brings our simulated power spectra into better agreement with the observational data of Viel et al (2013). At z = 5, the adopted F is the same as obtained by Boera et al (2019). We also show results where the optical depth in different simulations uses the same scaling factor, so all simulations have the same UVB.…”