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

Abstract

We compare a sample of five high-resolution, high S/N Lyα forest spectra of bright 6 < z <∼ 6.5 QSOs aimed at spectrally resolving the last remaining transmission spikes at z > 5 with those obtained from mock absorption spectra from the Sherwood and Sherwood-Relics suites of hydrodynamical simulations of the intergalactic medium (IGM). We use a profile fitting procedure for the inverted transmitted flux, 1−F , similar to the widely used Voigt profile fitting of the transmitted flux F at lower redshifts, to characterise the transmission spikes that probe predominately underdense regions of the IGM. We are able to reproduce the width and height distributions of the transmission spikes, both with optically thin simulations of the post-reionization Universe using a homogeneous UV background and full radiative transfer simulations of a late reionization model. We find that the width of the fitted components of the simulated transmission spikes is very sensitive to the instantaneous temperature of the reionized IGM. The internal structures of the spikes are more prominent in low temperature models of the IGM. The width distribution of the observed transmission spikes, which require high spectral resolution (≤ 8 km s −1 ) to be resolved, is reproduced for optically thin simulations with a temperature at mean density of T 0 = (11000 ± 1600, 10500 ± 2100, 12000 ± 2200) K at z = (5.4, 5.6, 5.8). This is weakly dependent on the slope of the temperature-density relation, which is favored to be moderately steeper than isothermal. In the inhomogeneous, late reionization, full radiative transfer simulations where islands of neutral hydrogen persist to z ∼ 5.3, the width distribution of the observed transmission spikes is consistent with the range of T 0 caused by spatial fluctuations in the temperature-density relation.

Dark photon dark matter in the presence of inhomogeneous structure

“…[57] for a review). Exotic heating of the IGM during the post-reionization epoch can therefore be constrained to the level of ≤ 0.5 eV / baryon for 2 z 6 [58][59][60][61][62]. Using this bound, ref.…”

“…where the sensitivity thresholds are (roughly) based on the signal-to-noise ratio of Ly-α observations [61]. For an alternative approach, we adopt a sensitivity function that varies smoothly with overdensity.…”

“…, where T 0 is the temperature at the mean density and γ ∼ 1.5 [58,61,65]. This problem is complicated by the fact that the average local neutral hydrogen fraction n H is not a known quantity; to leading order the Universe is fully ionized at these redshifts, and thus naïvelyn H ∼ 0.…”

“…[63] to fix e.g. τ eff (z = 1.9) ∼ 0.1. , from [61] and used the measurements in ref. [63] to normalize the optical depth at each redshift.…”

Radio detection of VIK J2318−3113, the most distant radio-loud quasar (z = 6.44)

“…These sources have already proved to be very useful tools for investigating the intergalactic medium (IGM) at early cosmic times through the absorption of their optical spectra bluewards of Lyα (e.g. Kashikawa et al 2006;Gaikwad et al 2020). Moreover, the mere presence of such powerful and massive objects in the primordial Universe places strong constraints on theoretical models describing the evolution and the accretion rate of supermassive black holes (SMBHs; e.g.…”