Abstract
ABSTRACT We compare a sample of five high-resolution, high S/N Ly α 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 Sherwoodand Sherwood–Relics simulation 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 characterize 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 T0 = (11 000 ± 1600, 10 500 ± 2100, 12 000 ± 2200) K at z = (5.4, 5.6, 5.8). This is weakly dependent on the slope of the temperature-density relation, which is favoured 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 T0 caused by spatial fluctuations in the temperature–density relation.
Highlights
The reionization of intergalactic H i and He i by ultraviolet photons from stars and black holes in the first galaxies is one of the major phase transitions of the universe
For the reionization and thermal history models we consider in this work, the spike statistics are only very weakly affected by pressure (Jeans) smoothing at the typical gas densities probed by the Lyα transmission spikes (Gnedin & Hui 1998; Theuns et al 2000; Peeples et al 2010; Kulkarni et al 2015; Lukic et al 2015; Nasir et al 2016; Maitra et al 2019; Wu et al 2019)
7 The mean transmitted flux in hot, cold and default models is matched to that in the observed spectra to account for the uncertainty in the continuum placement and UV background amplitude, see appendix ??. 8 We find that the flux power spectrum (FPS) and Pseudo Column Density Distribution Function (pCDDF) statistics are sensitive to continuum fitting uncertainty and ΓHI, whereas the spike width distribution is less sensitive to continuum placement and ΓHI
Summary
The reionization of intergalactic H i and He i by ultraviolet photons from stars and black holes in the first galaxies is one of the major phase transitions of the universe Garaldi et al (2019) found that the spike shape (especially the widths of the spikes) appeared to be only weakly correlated with the temperature of the IGM We revisit this question here with a larger sample of higher resolution, higher quality Lyα forest spectra which we compare to high-resolution hydrodynamical simulations of the IGM using the Sherwood and Sherwood-Relics simulation suites. Once we have established this we investigate the effect of inhomogeneous reionization in more physically motivated, spatially inhomogeneous H i reionization simulations including radiative transfer (see Kulkarni et al 2019b; Keating et al 2019) Another problem when comparing simulated and observed Lyα forest spectra is the accurate characterisation of the transmission spike properties. ΓHI expressed in units of 10−12 s−1 is denoted by Γ12
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