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We present the Sherwood–Relics simulations, a new suite of large cosmological hydrodynamical simulations aimed at modelling the intergalactic medium (IGM) during and after the cosmic reionization of hydrogen. The suite consists of over 200 simulations that cover a wide range of astrophysical and cosmological parameters. It also includes simulations that use a new lightweight hybrid scheme for treating radiative transfer effects. This scheme follows the spatial variations in the ionizing radiation field, as well as the associated fluctuations in IGM temperature and pressure smoothing. It is computationally much cheaper than full radiation hydrodynamics simulations, and circumvents the difficult task of calibrating a galaxy formation model to observational constraints on cosmic reionization. Using this hybrid technique, we study the spatial fluctuations in IGM properties that are seeded by patchy cosmic reionization. We investigate the relevant physical processes and assess their impact on the z > 4 Lyman-α forest. Our main findings are: (i) consistent with previous studies patchy reionization causes large-scale temperature fluctuations that persist well after the end of reionization, (ii) these increase the Lyman-α forest flux power spectrum on large scales, and (iii) result in a spatially varying pressure smoothing that correlates well with the local reionization redshift. (iv) Structures evaporated or puffed up by photoheating cause notable features in the Lyman-α forest, such as flat-bottom or double-dip absorption profiles. [ABSTRACT FROM AUTHOR]

Recent determinations of the mean free path of ionizing photons (mfp) in the intergalactic medium (IGM) at z = 6 are lower than many theoretical predictions. In order to gain insight, we investigate the evolution of the mfp in our new massive fully coupled radiation-hydrodynamics cosmological simulation of reionization: Cosmic Dawn III (CoDa III). CoDa III's scale (⁠|$\rm 94^3 \, cMpc^3$|⁠) and resolution (⁠|$\rm 8192^3$| grid) make it particularly suitable to study the IGM during reionization. The simulation was performed with ramses - cudaton on Summit, and used 13 1072 processors coupled to 24 576 GPUs, making it the largest reionization simulation, and largest ever ramses simulation. A superior agreement with global constraints on reionization is obtained in CoDa III over Cosmic Dawn II (CoDa II), especially for the evolution of the neutral hydrogen fraction and the cosmic photoionization rate, thanks to an improved calibration, later end of reionization (z = 5.6), and higher spatial resolution. Analysing the mfp, we find that CoDa III reproduces the most recent observations very well, from z = 6 to z = 4.6. We show that the distribution of the mfp in CoDa III is bimodal, with short (neutral) and long (ionized) mfp modes, due to the patchiness of reionization and the coexistence of neutral versus ionized regions during reionization. The neutral mode peaks at sub-kpc to kpc scales of mfp, while the ionized mode peak evolves from 0.1 Mpc  h −1 at z = 7 to ∼10 Mpc  h −1 at z = 5.2. Computing the mfp as the average of the ionized mode provides the best match to the recent observational determinations. The distribution reduces to a single neutral (ionized) mode at z > 13 (z < 5). [ABSTRACT FROM AUTHOR]

Our understanding of the intergalactic medium at redshifts z  = 5–6 has improved considerably in the last few years due to the discovery of quasars with z > 6 that enable Lyman-α forest studies at these redshifts. A realization from this has been that hydrogen reionization could end much later than previously thought, so that large 'islands' of cold, neutral hydrogen could exist in the IGM at redshifts z  = 5–6. By using radiative transfer simulations of the IGM, we consider the implications of the presence of these neutral hydrogen islands for the 21-cm power spectrum signal and its potential detection by experiments such as hera, ska, lofar , and mwa. In contrast with previous models of the 21-cm signal, we find that thanks to the late end of reionization the 21-cm power in our simulation continues to be as high as |$\Delta ^2_{21}=10~\mathrm{mK}^2$| at k ∼ 0.1  h  cMpc−1 at z  = 5–6. This value of the power spectrum is several orders of magnitude higher than that in conventional models considered in the literature for these redshifts. Such high values of the 21-cm power spectrum should be detectable by hera and ska1-low in ∼1000 h, assuming optimistic foreground subtraction. This redshift range is also attractive due to relatively low sky temperature and potentially greater abundance of multiwavelength data. [ABSTRACT FROM AUTHOR]

A long (110 cMpc  h−1) and deep absorption trough in the Ly α forest has been observed extending down to redshift 5.5 in the spectrum of ULAS J0148+0600. Although no Ly α transmission is detected, Ly β spikes are present which has led to claims that the gas along this trough must be ionized. Using high-resolution cosmological radiative transfer simulations in large volumes, we show that in a scenario where reionization ends late (z ∼ 5.2), our simulations can reproduce troughs as long as observed. In this model, we find that the troughs are caused by islands of neutral hydrogen. Small ionized holes within the neutral islands allow for the transmission of Ly β. We have also modelled the Ly α emitter population around the simulated troughs, and show that there is a deficit of Ly α emitters close to the trough as is observed. [ABSTRACT FROM AUTHOR]

We calibrate here cosmological radiative transfer simulations with aton/ramses with a range of measurements of the Ly α opacity from Quasi-Stellar Objects (QSO) absorption spectra. We find the Ly α opacity to be very sensitive to the exact timing of hydrogen reionization. Models reproducing the measured evolution of the mean photoionization rate and average mean free path reach overlap at z ~ 7 and predict an accelerated evolution of the Ly α opacity at z > 6 consistent with the rapidly evolving luminosity function of Ly α emitters in this redshift range. Similar to 'optically thin' simulations our full radiative transfer simulations fail, however, to reproduce the high-opacity tail of the Ly α opacity PDF (probability distribution function) at z > 5. We argue that this is due to spatial UV fluctuations in the post-overlap phase of reionization on substantially larger scales than predicted by our source model, where the ionizing emissivity is dominated by large numbers of sub-L* galaxies. We further argue that this suggests a significant contribution to the ionizing UV background by much rarer bright sources at high redshift. [ABSTRACT FROM AUTHOR]

In a series of three papers, the dynamical interplay between environments and dark matter haloes is investigated, while focusing on the dynamical flows through the virtual virial sphere. It relies on both cosmological simulations, to constrain the environments, and an extension to the classical matrix method to derive the responses of the halo. A companion paper (Paper I) showed how perturbation theory allows us to propagate the statistical properties of the environment to an ensemble description of the dynamical response of the embedded halo. The current paper focuses on the statistical characterization of the environments surrounding haloes, using a set of large-scale simulations; the large statistic of environments presented here allows us to put quantitative and statistically significant constrains on the properties of flows accreted by haloes. The description chosen in this paper relies on a ‘fluid’ halocentric representation. The interactions between the halo and its environment are investigated in terms of a time-dependent external tidal field and a source term characterizing the infall. The former accounts for fly bys and interlopers. The latter stands for the distribution function of the matter accreted through the virial sphere. The method of separation of variables is used to decouple the temporal evolution of these two quantities from their angular and velocity dependence by means of projection on a 5D basis. It is shown that how the flux densities of mass, momentum and energy can provide an alternative description to the 5D projection of the source. Such a description is well suited to regenerate synthetic time lines of accretion which are consistent with environments found in simulations as discussed in the Appendix . The method leading to the measurements of these quantities in simulations is presented in detail and applied to 15 000 haloes, with masses between and evolving between and 0. The influence of resolution, class of mass, and selection biases are investigated with higher resolution simulations. The emphasis is put on the one- and two-point statistics of the tidal field, and of the flux density of mass, while the full characterization of the other fields is postponed to Paper III. The net accretion at the virial radius is found to decrease with time. This decline results from both an absolute decrease of infall and a growing contribution of outflows. Infall is found to be mainly radial and occurring at velocities ∼0.75 times the virial velocity. Outflows are also detected through the virial sphere and occur at lower velocities on more circular orbits. The external tidal field is found to be strongly quadrupolar and mostly stationary, possibly reflecting the distribution of matter in the halo's near environment. The coherence time of the small-scale fluctuations of the potential hints a possible anisotropic distribution of accreted satellites. The flux density of mass on the virial sphere appears to be more clustered than the potential, while the shape of its angular power spectrum seems stationary. Most of these results are tabulated with simple fitting laws and are found to be consistent with published work, which rely on a description of accretion in terms of satellites. [ABSTRACT FROM AUTHOR]

We investigate statistically the dynamical consequences of cosmological fluxes of matter and related moments on progenitors of today's dark matter haloes. These haloes are described as open collisionless systems which do not undergo strong interactions anymore. Their dynamics is described via canonical perturbation theory which accounts for two types of perturbations: the tidal field corresponding to flybys and accretion of dark matter through the outer boundary of the halo. The non-linear evolution of both the entering flux and the particles of the halo is followed perturbatively. The dynamical equations are solved linearly, order by order, projecting on a bi-orthogonal basis to consistently satisfy the field equation. Since our perturbative solution of the Boltzmann–Poisson is explicit, we obtain, as a result, expressions for the N-point correlation function of the response of the halo to the perturbative environment. It allows statistical predictions for the ensemble distribution of the inner dynamical features of haloes. We demonstrate the feasibility of the implementation via a simple example in Appendix B . We argue that the fluid description accounts for the dynamical drag and the tidal stripping of incoming structures. We discuss the realm of non-linear problems which could be addressed statistically by such a theory, such as differential dynamical friction, tidal stripping and the self-gravity of objects within the virial sphere. The secular evolution of open galactic haloes is investigated: we derive the kinetic equation which governs the quasi-linear evolution of dark matter profile induced by infall and its corresponding gravitational correlations. This yields a Fokker–Planck-like equation for the angle-averaged underlying distribution function. This equation has an explicit source term accounting for the net infall through the virial sphere. Under the assumption of ergodicity we then relate the corresponding source, drift and diffusion coefficients for the ensemble-average distribution to the underlying cosmic two-point statistics of the infall and discuss possible applications. The internal dynamics of substructures within galactic haloes (distortion, clumps as traced by Xray emissivity, weak lensing, dark matter annihilation, tidal streams, etc.), and the implication for the disc (spiral structure, warp, etc.) are then briefly discussed. We show how this theory could be used to (i) observationally constrain the statistical nature of the infall, (ii) predict the observed distribution and correlations of substructures in upcoming surveys, (iii) predict the past evolution of the observed distribution of clumps and finally (iv) weight the relative importance of the intrinsic (via the unperturbed distribution function) and external (tidal and/or infall) influence of the environment in determining the fate of galaxies. We stress that our theory describes the perturbed distribution function (mean profile removed) directly in phase space. [ABSTRACT FROM AUTHOR]