Measurement of the spatial distribution of neutral hydrogen via the redshifted 21 cm line promises to revolutionize our knowledge of the epoch of reionization and the first galaxies, and may provide a powerful new tool for observational cosmology from redshifts 1<z<4 . In this review we discuss recent advances in our theoretical understanding of the epoch of reionization (EoR), the application of 21 cm tomography to cosmology and measurements of the dark energy equation of state after reionization, and the instrumentation and observational techniques shared by 21 cm EoR and post reionization cosmology machines. We place particular emphasis on the expected signal and observational capabilities of first generation 21 cm fluctuation instruments.
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…
It has been recently shown that the astrophysics of reionization can be extracted from the Ly$α$ forest power spectrum by marginalizing the memory of reionization over cosmological information. This impact of cosmic reionization on the Ly$α$ forest power spectrum can survive cosmological time scales because cosmic reionization, which is inhomogeneous, and subsequent shocks from denser regions can heat the gas in low-density regions to $\sim 3\times10^4$ K and compress it to mean-density. Current approach of marginalization over the memory of reionization, however, is not only model-dependent, …
Motivated by the desire for wide-field images with well-defined statistical properties for 21cm cosmology, we implement an optimal mapping pipeline that computes a maximum likelihood estimator for the sky using the interferometric measurement equation. We demonstrate this direct optimal mapping with data from the Hydrogen Epoch of Reionization (HERA) Phase I observations. After validating the pipeline with simulated data, we develop a maximum likelihood figure-of-merit for comparing four sky models at 166MHz with a bandwidth of 100kHz. The HERA data agree with the GLEAM catalogs to <10%. After…
The Challenge of Observing Patchy Reionization with CMB Optical-Depth Fluctuations
The University of Chicago（芝加哥大学）；Institute for Advanced Study（高等研究院）；Fermi National Accelerator Laboratory（费米国家加速器实验室）；Kavli Institute for Cosmological Physics（卡弗里宇宙物理学研究所）
A near-future detection of the 21cm signal from the epoch of reionization will provide unique opportunities to probe the underlying cosmology, provided that such cosmological information can be extracted with precision. To this end, we further develop effective field theory (EFT) inspired techniques for the 21cm brightness temperature field during the epoch of reionization, incorporating renormalized bias and a treatment of redshift space distortions. Notably, we confirm that in redshift space, measures of the 21cm brightness, e.g the power spectrum, should have irreducible contributions that …
Reionization of the cosmic neutral hydrogen by the first stars in the Universe is an inhomogeneous process which produces spatial fluctuations in free electron density. These fluctuations lead to observable signatures in cosmological probes like the cosmic microwave background (CMB). We explore the effect of the electron density fluctuations on CMB using photon-conserving semi-numerical simulations of reionization named \texttt{SCRIPT}. We show that the amplitude of the kinematic Sunyaev-Zeldovich (kSZ) and $B$-mode polarization signal depends on the patchiness in the spatial distribution of e…
Large Lyman-alpha opacity fluctuations and low CMB tau in models of late reionization with large islands of neutral hydrogen extending to z<5.5
高红移类星体光谱显示星系际介质的Ly-alpha不透明度在z>~5.5的大尺度上有很大的空间起伏。我们提出了一个由星系驱动的宇宙再电离的辐射转移模拟，再现了这种大的散射和快速演变的Ly-alpha不透明度分布在5<z <6. The simulation also reproduces the low Thomson scattering optical depth reported by the latest CMB measurement and is consistent with the observed short near-zones and strong red damping wings in the highest-redshift QSOs. It also matches the rapid disappearance of observed Ly-alpha emission by galaxies at z>~6。在我们的模型中，再电离在z=5.3时完成，宇宙体积的50%在z=7时电离。在这样一个晚期再电离模型中，与Ly-alpha森林数据的一致性需要星系电离发射率的快速演变，其峰值在z~6.8。再电离的后期导致光电离率和中性氢分数在红移低至z<~5.5处的大散射，并具有大的残余中性“岛”，其可以产生非常长的冈恩-彼得森槽，类似于数据中所看到的…
Semi-numeric simulations of helium reionization and the fluctuating radiation background
最近He II Lyman-alpha森林观测从2.0 < z < 3.2 show large fluctuations in the optical depth at z >2.7。这些结果指出，波动的氦电离背景，这可能是由于结束氦再电离的这个时代。我们提出了一个快速的，半数值的过程来近似详细的宇宙学模拟。我们计算的暗物质晕的分布，氦的电离态，和密度场在z = 3与最近的模拟广泛的协议。鉴于我们的速度和灵活性，我们调查了一系列电离源和活跃的类星体处方。跨越一个大面积的参数空间，我们发现订单的数量级波动的He II电离率在后再电离制度。在再电离过程中，波动甚至更强，并开发一个双峰分布，与半解析模型和氢当量。这些分布表明，即使在显着的He II分数的低水平电离背景。
The epoch of reionization probes the state of our universe when the very first stars formed and ionized the hydrogen atoms in the surrounding medium. Since the epoch has not yet been probed observationally, it is often called the "final frontier" of observational cosmology. This final frontier is attracting a lot of attention because of the availability of a large number of telescopes in a wide variety of wavebands. This review article summarizes some of the concepts required to understand the interesting physics of reionization and how to analyze the high-redshift universe using related obser…
During the last decades, our understanding of the universe has reached a remarkable level, being able to test cosmological predictions with an astonishing precision. Nonetheless, the nature, composition, mass and interactions of the Dark Matter still remain unknown, presenting one of the most intriguing conundrums in current cosmology. In this doctoral thesis, signatures of Dark Matter candidates which can leave an impact on the process of formation of structures and on the evolution of the Intergalactic Medium are studied. This thesis is organized in three parts. Part I is devoted to a broad …
Cosmological simulations of reionization often treat radiative transfer by solving for the monopole and dipoles of the intensity field and by making ansatz for the quadrupole moments to close the system of equations. We investigate the accuracy of the most common closure methods, i.e. Eddington tensor choices. We argue that these algorithms are most likely to err after reionization and study quasi-analytic test problems mimicking these situations: large-scale post-reionization ionizing background fluctuations and radiative transfer in a predominantly ionized medium with discrete absorbers. We …
Small-scale density fluctuations can significantly affect reionization but are typically modelled quite crudely. Unresolved fluctuations in numerical simulations and analytical calculations are included using a gas clumping factor, typically assumed to be independent of the local environment. In Paper I, we presented an improved, local density-dependent model for the sub-grid gas clumping. Here we extend this using an empirical stochastic model based on the results from high-resolution numerical simulations which fully resolve all relevant fluctuations. Our model reproduces well both the mean …
We propose a new reionization probe that uses cosmic microwave background (CMB) observations; the cross-correlation between fluctuations in the CMB optical depth which probes the integrated electron density, $δτ$, and the Compton $y$-map which probes the integrated electron pressure. This cross-correlation is much less contaminated than the $y$-map power spectrum by late-time cluster contributions. In addition, this cross-correlation can constrain the temperature of ionized bubbles while the optical-depth fluctuations and kinetic SZ effect can not. We measure this new observable using a Planck…
We present a computationally efficient and fast semi-numerical technique for simulating the Lyman-$α$ (Ly$α$) absorption optical depth in presence of neutral hydrogen "islands" left over from reionization at redshifts $5 \lesssim z \lesssim 6$. The main inputs to the analysis are (i) a semi-numerical photon-conserving model of ionized regions during reionization (named SCRIPT) along with a prescription for simulating the shadowing by neutral islands and (ii) the fluctuating Gunn-Peterson approximation to model the Ly$α$ absorption. Our model is then used for simulating the large-scale fluctuat…
Interpreting the HI 21-cm cosmology maps through Largest Cluster Statistics III: Impact of the lightcone effect
Indian Institute of Technology Indore（印度印多尔理工学院）；Stellenbosch University（斯泰伦博斯大学）；University of Groningen（格罗宁根大学）；The Open University of Israel（以色列开放大学）
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…
In this paper we investigate how the Reionization process is affected by early galaxy formation in different cosmological scenarios. We use a semi-analytic model with suppressed initial power spectra to obtain the UV Luminosity Function in thermal Warm Dark Matter and sterile neutrino cosmologies. We retrace the ionization history of intergalactic medium with hot stellar emission only, exploiting fixed and variable photons escape fraction models ($f_{esc}$). For each cosmology, we find an upper limit to fixed $f_{esc}$, which guarantees the completion of the process at $z<6.7$. The analysis is…
