It is generally taken for granted that reionization has completed by z=6, due to the detection of flux in the Lyman alpha forest at redshifts z<6. However, since reionization is expected to be highly inhomogeneous, much of the spectra pass through just the ionized component of the intergalactic medium (IGM) even for non-negligible values of the volume-weighted mean neutral hydrogen fraction, x_HI. We study the expected signature of an incomplete reionization at z ~ 5--6, using very large-scale (2 Gpc) seminumeric simulations. We find that ruling out an incomplete reionization is difficult at these redshifts since: (1) quasars reside in biased regions of the ionization field, with fewer surrounding HI patches than implied by the global mean, x_H; (2) absorption from the residual neutral hydrogen inside the ionized IGM generally dominates over the absorption from the remaining HI regions; (3) modeling the Lyman alpha forest and its redshift evolution even in just the ionized IGM is very difficult, and nearly impossible to do a priori. We propose using the fraction of pixels which are dark as a simple, nearly model-independent upper limit on x_HI. Alternately, the size distribution of regions with no detectable flux (dark gaps) can be used to place a more model dependent constraint. Either way, the current sample of quasars is statistically insufficient to constrain x_HI at z~6 to even the 10 per cent level. At z~5, where there are more available sightlines and the forest is less dark, constraining x_HI < 0.1 might be possible given a large dynamic range from very deep spectra and/or the Lyman beta forest. We conclude with the caution against over-interpreting the observations. There is currently no direct evidence that reionization was complete by z ~ 5-6.
We present a comparison between several observational tests of the post-reionization IGM and the numerical simulations of reionization completed under the Cosmic Reionization On Computers (CROC) project. The CROC simulations match the gap distribution reasonably well, and also provide a good match for the distribution of peak heights, but there is a notable lack of wide peaks in the simulated spectra and the flux PDFs are poorly matched in the narrow redshift interval 5.5<z<5.7, with the match at other redshifts being significantly better, albeit not exact. Both discrepancies are related: simu…
We have run a new suite of simulations that solve hydrodynamics and radiative transfer simultaneously to study helium II reionization. Our suite of simulations employs various models for populating quasars inside of dark matter halos, which affect the He II reionization history. In particular, we are able to explore the impact that differences in the timing and duration of reionization have on observables. We examine the thermal signature that reionization leaves on the IGM, and measure the temperature-density relation. As previous studies have shown, we confirm that the photoheating feedback …
The thermal state of the post-reionization IGM is sensitive to the timing of reionization and the nature of the ionizing sources. We have modelled here the thermal state of the IGM in cosmological radiative transfer simulations of a realistic, extended, spatially inhomogeneous hydrogen reionization process, carefully calibrated with Ly-alpha forest data. We compare these with cosmological simulations run using a spatially homogeneous ionizing background. The simulations with a realistic growth of ionized regions and a realistic spread in reionization redshifts show, as expected, significant sp…
Because the same massive stars that reionized the intergalactic medium (IGM) inevitably exploded as supernovae that polluted the Universe with metals, the history of cosmic reionization and enrichment are intimately intertwined. While the overly sensitive Ly-alpha transition completely saturates in a neutral IGM, strong low-ionization metal lines like the MgII 2796,2804 doublet will give rise to a detectable `metal-line forest' if the metals produced during reionization (Z ~ 10^{-3}Z_sol) permeate the neutral IGM. We simulate the MgII forest for the first time by combining a large hydrodynamic…
Recent years have brought more precise temperature measurements of the low-density intergalactic medium (IGM). These new measurements constrain the processes that heated the IGM, such as the reionization of H I and of He II. We present a semi-analytical model for the thermal history of the IGM that follows the photoheating history of primordial gas. Our model adopts a multizone approach that, compared to previous models, more accurately captures the inhomogeneous heating and cooling of the IGM during patchy reionization. We compare our model with recent temperature measurements spanning z = 1.…
We investigate self-shielding of intergalactic hydrogen against ionizing radiation in radiative transfer simulations of cosmic reionization carefully calibrated with Lyman alpha forest data. While self-shielded regions manifest as Lyman-limit systems in the post-reionization Universe, here we focus on their evolution during reionization (redshifts z=6-10). At these redshifts, the spatial distribution of hydrogen-ionizing radiation is highly inhomogeneous, and some regions of the Universe are still neutral. After masking the neutral regions and ionizing sources in the simulation, we find that t…
In this work we present a new hybrid method to simulate the thermal effects of the reionization in cosmological hydrodynamical simulations. The method improves upon the standard approach used in simulations of the intergalactic medium (IGM) and galaxy formation without a significant increase of the computational cost allowing for efficient exploration of the parameter space. The method uses a small set of phenomenological input parameters and combines a semi-numerical reionization model to solve for the topology of reionization and an approximate model of how reionization heats the IGM, with t…
During reionization, neutral hydrogen in the intergalactic medium (IGM) imprints a damping wing absorption feature on the spectrum of high-redshift quasars. A detection of this signature provides compelling evidence for a significantly neutral Universe, and enables measurements of the hydrogen neutral fraction $x_{\rm HI}(z)$ at that epoch. Obtaining reliable quantitative constraints from this technique, however, is challenging due to stochasticity induced by the patchy inside-out topology of reionization, degeneracies with quasar lifetime, and the unknown unabsorbed quasar spectrum close to r…
We assess the probable redshift (z_rei ~ 7) for full reionization of the intergalactic medium (IGM) using a prescription for the co-moving star-formation-rate (SFR) density (rho_SFR) required to maintain photoionization against recombination. Our newly developed on-line reionization simulator allows users to assess the required SFR and ionization histories, using a variety of assumptions for galactic and stellar populations, IGM clumping factor and temperature, and LyC escape fraction. The decline in high-redshift galaxy candidates and Lya emitters at z = 6-8 suggests a rising neutral fraction…
The large opacity fluctuations in the $z > 5.5$ Ly$α$ forest may indicate inhomogeneous progress of reionization. To explain the observed large scatter of the effective Ly$α$ optical depth ($τ_{\rm eff}$) of the intergalactic medium (IGM), fluctuation of UV background ($Γ$ model) or the IGM gas temperature ($T$ model) have been proposed, which predict opposite correlations between $τ_{\rm eff}$ and galaxy density. In order to address which model can explain the large scatter of $τ_{\rm eff}$, we search for Ly$α$ emitters (LAEs) around two (J1137+3549 and J1602+4228) quasar sightlines with $τ_{…
The highly neutral inter-galactic medium (IGM) during the Epoch of Reionization (EoR) is expected to suppress Ly$α$ emission with damping-wing absorption, causing nearly no Ly$α$ detection from star-forming galaxies at $z{\sim}8$. However, spectroscopic observations of the 4 brightest galaxies (${\rm H}_{160}{\sim}25$ mag) at these redshifts do reveal prominent Ly$α$ line, suggesting locally ionised IGM. In this paper, we explore the Ly$α$ IGM transmission and environment of bright galaxies during the EoR using the Meraxes semi-analytic model. We find brighter galaxies to be less affected by d…
Due to the large cross section of Ly$α$ photons with hydrogen, Lyman Alpha Emitters (LAEs) are sensitive to the presence of neutral hydrogen in the intergalactic medium (IGM) during the Epoch of Reionization (EoR): the period in the Universe's history where neutral hydrogen in the IGM is ionized. The correlation of the ionized regions in the IGM with respect to the underlying intrinsic LAEs has a pronounced effect on the number of observed LAEs and their apparent clustering. As a result, observations of LAEs during the EoR can be used as a probe of the EoR morphology. Here we build on previous…
I present our analysis of the 21cm power spectrum upper limits from the HERA radio interferometer, published in HERA Collaboration et al. 2022. We use the recent limits to constrain reionization and the properties of the IGM and galaxies in the early universe. I focus in particular on the possibility of a radio background in addition to the CMB (e.g. produced by early galaxies) which can lead to a stronger 21cm signal and is thus easier to constrain. I show what limits the HERA observations can put on these models and the IGM, and how this compares to existing constraints on the radio and X-ra…
Galaxy Underdensities Host the Clearest IGM Ly$α$ Transmission and Indicate Anisotropic Reionization
Steward Observatory, University of Arizona（亚利桑那大学斯图尔德天文台）；Department of Physics & Astronomy, University of California, Riverside（加州大学河滨分校物理与天文学系）；Department of Astronomy, The University of Texas at Austin（德克萨斯大学奥斯汀分校天文学系）；School of Earth and Space Exploration, Arizona State University（亚利桑那州立大学地球与空间探索学院）；Cosmic Dawn Center(DAWN)（宇宙黎明中心）；Niels Bohr Institute, University of Copenhagen（哥本哈根大学尼尔斯玻尔研究所）
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 $4.0\lesssim z\lesssim5.2$. Using a sample of 15 high-resolution spectra, we measure the flux power down to the smallest scales ever probed at these redshifts ($-1\lesssim \log(k/$km$^{-1}$s)$\lesssim -0.7$). 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 $T_{0}\sim7000$-80…
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 com…
Detecting neutral hydrogen structures in the intergalactic medium (IGM) during cosmic reionization via absorption (21 cm forest) against a background radiation is considered independent and complementary to the three-dimensional tomography and power spectrum techniques. The direct detection of this absorption requires very bright ($\gtrsim 10$-100 mJy) background sources at high redshifts ($z\gtrsim 8$), which are evidently rare; very long times of integration; or instruments of very high sensitivity. This motivates a statistical one-dimensional (1D) power spectrum approach along narrow sightl…
The detection of an unexpectedly large number of faint candidate quasars (QSO) at $z \gtrsim 4$ has motivated Madau and Haardt to investigate a reionization scenario in which active galactic nuclei dominate the photon budget at all times. Their analytical study reveals that this picture is in agreement with the evolution of the HI volume fraction in the intergalactic medium (IGM) and the optical depth to Thomson scattering of the cosmic microwave background. We employ a suite of hydrodynamical simulations post-processed with a radiative transfer code to further investigate the properties of su…
PAPER-64 Constraints On Reionization II: The Temperature Of The z=8.4 Intergalactic Medium
我们提出的约束的星系际介质（IGM）在z=8.4的动力学温度，并在模型上加热IGM在高红移与X射线发射的第一个崩溃的对象。这些约束条件是用半解析方法推导出来的，以探索唐纳德C。Backer Precision Array for Probing the Epoch of Reionization（PAPER），在Ali et al.（2015）的配套论文中提出。如果IGM的动力学温度显著低于宇宙微波背景（CMB）的温度，一般可以产生振幅为数百mK ^2的21 cm功率谱;因此，PAPER的新结果将IGM温度的下限定在z=8.4。考虑到IGM的未知电离状态，我们的测量发现IGM温度对于10%和85%之间的中性部分高于~5 K，对于15%和80%之间的中性部分高于~7 K，或者对于30%和70%之间的中性部分高于~10 K。我们还计算了加热的IGM，将提供所观察到的高红移星系人口，并发现，对于大多数模型，这些星系足以使IGM温度高于我们的下限。然而，有显着范围的参数空间，可以产生一个信号排除了PAPER测量;模型与陡峭的下降，在恒星形成率密度在高红移或相对较低的价值观的X射线恒星形成率效率的高红移星系通常是不受欢迎的。的纸测量是一致的（但不约束）的氢自旋温度高于CMB温度，这种情况下，我们发现一般预测，如果星系暗于目前的检测极限的光学/近红外测量包括在计算中的X射线加热。
We present semi-analytic models of the epoch of reionization focusing on the differences between continuous and bursty star formation (SF). Our model utilizes physically motivated analytic fits to 1D radiative transfer simulations of HII regions around dark matter halos in a representative cosmic volume. Constraining our simulations with observed and extrapolated UV luminosity functions of high redshift galaxies, we find that for a fixed halo mass, stellar populations forming in bursty models produce larger HII regions which leave behind long-lived relic HII regions which are able to maintain …
Recent measurements of the ionizing photon mean free path ($λ_{912}^{\rm mfp}$) at $5 < z < 6$ suggest that the IGM was rapidly evolving at those times. We use radiative transfer simulations to explore the implications for reionization, with a focus on the short value of $λ_{912}^{\rm mfp} = 3.57^{+3.09}_{-2.14}$ cMpc/$h$ at $z=6$. We introduce a model for sub-resolution ionizing photon sinks based on radiative hydrodynamics simulations of small-scale IGM clumping. We argue that the rapid evolution in $λ_{912}^{\rm mfp}$ at $z=5-6$, together with constraints on the metagalactic ionizing backgr…
Fast radio bursts (FRBs) are millisecond-duration radio transients and can be used as a cosmological probe. However, the dispersion measure (DM) contributed by intergalactic medium (IGM) is hard to be distinguished from other components. In this paper, we use the IllustrisTNG simulation to realistically estimate the $DM_{\rm IGM}$ up to $z\sim 9$. We find $DM_{\rm IGM} = 892^{+721}_{-270}$ pc cm$^{-3}$ at $z=1$. The probability distribution of $DM_{\rm IGM}$ can be well fitted by a quasi-Gaussian function with a long tail. The tail is caused by the structures along the line of sight in IGM. Su…
The ultraviolet background (UVB) emitted by quasars and galaxies governs the ionization and thermal state of the intergalactic medium (IGM), regulates the formation of high-redshift galaxies, and is thus a key quantity for modeling cosmic reionization. The vast majority of cosmological hydrodynamical simulations implement the UVB via a set of spatially uniform photoionization and photoheating rates derived from UVB synthesis models. We show that simulations using canonical UVB rates reionize and, perhaps more importantly, spuriously heat the IGM, much earlier z ~ 15 than they should. This prob…
JWST ASPIRE: How Did Galaxies Complete Reionization? Evidence for Excess IGM Transmission around ${\rm [O\,{\scriptstyle III}]}$ Emitters during Reionization
The amplitude of the ionizing background that pervades the intergalactic medium (IGM) at the end of the epoch of reionization provides a valuable constraint on the emissivity of the sources which reionized the Universe. While measurements of the ionizing background at lower redshifts rely on a simulation-calibrated mapping between the photoionization rate and the mean transmission of the Ly$α$ forest, at $z\gtrsim6$ the IGM becomes increasingly opaque, and transmission arises solely in narrow spikes separated by saturated Gunn-Peterson troughs. In this regime, the traditional approach of measu…
HST Spectral Observations near the He II Ly-alpha Break: Implications for He II Reionization
能够研究IGM He II的类星体非常罕见，因为它们必须沿着没有大量氢吸收的视线处于高红移，但最近的工作显着扩大了已知的此类类星体的数量。我们分析了24个来自HST的高红移（z=3.1-3.9）低分辨率He II类星体的光谱，发现它们的He II Gunn-Peterson槽表明排除了非常早和非常晚的再电离模型，支持z~3的再电离红移。虽然数据的质量是不足以揭示细节，如预期的红移演变的氦不透明度，我们得到的第一个合奏措施的氦不透明度在高红移平均在许多视线：τ =4.90在z~3.3。我们还发现，从He II再电离开始观察IGM红翼吸收是非常困难的，但取决于再电离的红移和电离区的大小，用当前一代的紫外光谱仪在某些物体中可能这样做。
