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Enlightening our understanding of the first galaxies responsible for driving reionization requires detecting the 21-cm signal from neutral hydrogen. Interpreting the wealth of information embedded in this signal requires Bayesian inference. Parameter inference from the 21-cm signal is primarily restricted to the spherically averaged power spectrum (1D PS) owing to its relatively straightforward derivation of an analytic likelihood function enabling traditional Monte Carlo Markov Chain approaches. However, in recent years, simulation-based inference (SBI) has become feasible which removes the necessity of having an analytic likelihood, enabling more complex summary statistics of the 21-cm signal to be used for Bayesian inference. In this work, we use SBI, specifically marginal neural ratio estimation to learn the likelihood-to-evidence ratio with swyft , to explore parameter inference using the cylindrically averaged 2D PS. Since the 21-cm signal is anisotropic, the 2D PS should yield more constraining information compared to the 1D PS which isotropically averages the signal. For this, we consider a mock 1000 h observation of the 21-cm signal using the Square Kilometre Array and compare the performance of the 2D PS relative to the 1D PS. Additionally, we explore two separate foreground mitigation strategies, perfect foreground removal and wedge avoidance. We find the 2D PS outperforms the 1D PS by improving the marginalized uncertainties on individual astrophysical parameters by up to |$\sim 30\!-\!40$|  per cent irrespective of the foreground mitigation strategy. Primarily, these improvements stem from how the 2D PS distinguishes between the transverse, |$k_{\perp }$|⁠ , and redshift-dependent, |$k_{\parallel }$|⁠ , information which enables greater sensitivity to the complex reionization morphology. [ABSTRACT FROM AUTHOR]

Detecting the 21-cm signal at |$z\gtrsim 6$| will reveal insights into the properties of the first galaxies responsible for driving reionization. To extract this information, we perform parameter inference with three-dimensional simulations of the 21-cm signal embedded within a Bayesian inference pipeline. Presently, when performing inference, we must choose which sources of uncertainty to sample and which to hold fixed. Since the astrophysics of galaxies is much more uncertain than that of the underlying halo-mass function (HMF), we typically parametrize and model the former while fixing the latter. However, doing so may bias our inference of the galaxy properties. In this work, we explore the consequences of assuming an incorrect HMF and quantify the relative biases on our inferred astrophysical model parameters when considering the wrong HMF. We then relax this assumption by constructing a generalized five parameter HMF model and simultaneously recover it with our underlying astrophysical model. For this, we use 21cmfast and perform simulation-based inference using marginal neural ratio estimation to learn the likelihood-to-evidence ratio with Swyft. Using a mock 1000-h observation of the 21-cm power spectrum from the forthcoming Square Kilometre Array, conservatively assuming foreground wedge avoidance, we find that assuming the incorrect HMF can bias the recovered astrophysical parameters by up to |$\sim 3{\!-\!}4\sigma$| even when including independent information from observed luminosity functions. Using our generalized HMF model, although we recover our astrophysical parameters with a factor of |$\sim 2{\!-\!}4$| larger marginalized uncertainties, the constraints are unbiased, agnostic to the underlying HMF and therefore more conservative. [ABSTRACT FROM AUTHOR]

This article is a correction to a previous study on the forecast of the epoch of reionization (EoR) history in cosmology. The correction states that there was a mistake in the calculation of the standard deviation, which led to an overly optimistic inference forecast. The corrected results show that the EoR history is constrained to within a narrower range, improving the current limits. The article provides updated versions of the affected figures. [Extracted from the article]

Lyman-alpha (Ly α) emission from galaxies is currently our most promising probe for constraining when and how reionization began, and thus when the first galaxies formed. At z > 7, the majority of galaxies detected with Ly α are in candidate overdensities. Here, we quantify the probability of these galaxies residing in large ionized bubbles. We create (1.6 Gpc)3 intergalactic medium (IGM) simulations: sufficient volume to robustly measure bubble size distributions around UV-bright galaxies and rare overdensities. We find |${M_{\small UV}}\lesssim -16$| galaxies and overdensities are ≳10–1000 × more likely to trace ionized bubbles compared to randomly selected positions. The brightest galaxies and strongest overdensities have bubble size distributions with highest characteristic size and least scatter. We compare two models: gradual reionization driven by numerous UV-faint galaxies versus rapid reionization by rarer brighter galaxies, producing larger bubbles at fixed neutral fraction. We demonstrate that recently observed z ∼ 7 overdensities are highly likely to trace large ionized bubbles, corroborated by their high Ly α detection rates. However, Ly α detections at z ≈ 8.7 in EGS and z  = 10.6 in GN-z11 are unlikely to trace large bubbles in our fiducial model – 11 and 7 per cent probability of >1 proper Mpc bubbles, respectively. Ly α detections at such high redshifts could be explained by: a less neutral IGM than previously expected; larger ionized regions at fixed neutral fraction; or if intrinsic Ly α flux is unusually strong in these galaxies. We discuss how to test these scenarios with JWST and prospects for upcoming wide-area surveys to distinguish between reionization models. [ABSTRACT FROM AUTHOR]

Recent years have witnessed rapid progress in observations of the epoch of reionization (EoR). These have enabled high-dimensional inference of galaxy and intergalactic medium (IGM) properties during the first billion years of our Universe. However, even using efficient, seminumerical simulations, traditional inference approaches that compute 3D lightcones on-the-fly can take 105 core hours. Here we present 21cmemu : an emulator of several summary observables from the popular 21cmfast simulation code. 21cmemu takes as input nine parameters characterizing EoR galaxies, and outputs the following summary statistics: (i) the IGM mean neutral fraction; (ii) the 21-cm power spectrum; (iii) the mean 21-cm spin temperature; (iv) the sky-averaged (global) 21-cm signal; (vi) the ultraviolet (UV) luminosity functions (LFs); and (vii) the Thomson scattering optical depth to the cosmic microwave background (CMB). All observables are predicted with sub- per cent median accuracy, with a reduction of the computational cost by a factor of over 104. After validating inference results, we showcase a few applications, including: (i) quantifying the relative constraining power of different observational data sets; (ii) seeing how recent claims of a late EoR impact previous inferences; and (iii) forecasting upcoming constraints from the sixth observing season of the Hydrogen Epoch of Reionization Array (HERA) telescope. 21cmemu is publicly available, and is included as an alternative simulator in the public 21cmmc sampler. [ABSTRACT FROM AUTHOR]

The fraction of ionizing photons that escape their host galaxies to ionize hydrogen in the intergalactic medium (IGM) is a critical parameter in analyses of the reionization era. In this paper, we use the meraxes semi-analytic galaxy formation model to infer the mean ionizing photon escape fraction and its dependence on galaxy properties through joint modelling of the observed high redshift galaxy population and existing constraints on the reionization history. Using a Bayesian framework, and under the assumption that escape fraction is primarily related to halo mass, we find that the joint constraints of the ultraviolet luminosity function, cosmic microwave background optical depth, and the Ly α forest require an escape fraction of |$(18\pm 5)$| per cent for galaxies within haloes of M ≲ 109 M⊙ and |$(5\pm 2)$| per cent for more massive haloes. In terms of galaxy properties, this transition in escape fraction occurs at stellar masses of M ⋆ ∼ 107 M⊙, nearly independent of redshift. As a function of redshift, reionization is dominated by the smaller M ⋆ ≲ 107 M⊙ galaxies with high escape fractions at z ≳ 6 and by the larger M ⋆ ≳ 107 M⊙ galaxies with lower escape fractions at z ≲ 6. Galaxies with star formation rates of 10−2.5 M⊙yr−1 to 10−1.5 M⊙yr−1 provide the dominant source of ionizing photons throughout reionization. Our results are consistent with recent direct measurements of a |$\sim 5~{{\ \rm per\ cent}}$| escape fraction from massive galaxies at the end of reionization and support the picture of low mass galaxies being the dominant sources of ionizing photons during reionization. [ABSTRACT FROM AUTHOR]

The patchy kinetic Sunyaev–Zel'dovich (kSZ) signal is an integral probe of the timing and morphology of the epoch of reionization (EoR). Recent observations have claimed a low signal-to-noise (S/N) measurement, with a dramatic increase in S/N expected in the near future. In this work, we quantify what we can learn about the EoR from the kSZ signal. We perform Bayesian inference by sampling galaxy properties and using forward-models of the kSZ as well as other EoR and galaxy observations in the likelihood. Including the recent kSZ measurement obtained by the South Pole Telescope (⁠|$\mathcal {D}_{3000}^{\textrm {pkSZ}} = 1.1_{-0.7}^{+1.1} \mu$| K2) shifts the posterior distribution in favour of faster and later reionization models, resulting in lower values of the optical depth to the cosmic microwave background: |$\tau _e = 0.052_{-0.008}^{+0.009}$| with a 68 per cent confidence interval (CI). The combined EoR and ultraviolet luminosity function observations also imply a typical ionizing escape fraction of |$0.04_{-0.03}^{+0.05}$| (95 per cent CI), without a strong dependence on halo mass. We show how the patchy kSZ power from our posterior depends on the midpoint and duration of reionization: a popular parametrization of EoR timing. For a given midpoint and duration, the EoR morphology only has a few per cent impact on the patchy kSZ power in our posterior. However, a physical model is needed to obtain tight constraints from the current low S/N patchy kSZ measurement, as it allows us to take advantage of complimentary high- z observations. Future high S/N detections of the patchy kSZ should decrease the current uncertainties on the timing of the EoR by factors of ∼2–3. [ABSTRACT FROM AUTHOR]

Using a semi-analytic galaxy formation model, we study analogues of eight z ≳ 12 galaxies recently discovered by James Webb Space Telescope (JWST). We select analogues from a cosmological simulation with a (311 cMpc)3 volume and an effective particle number of 1012 enabling the resolution of every atomic-cooling galaxy at z ≤ 20. We vary model parameters to reproduce the observed ultraviolet (UV) luminosity function at 5 < z < 13, aiming for a statistically representative high-redshift galaxy mock catalogue. Using the forward-modelled JWST photometry, we identify analogues from this catalogue and study their properties as well as possible evolutionary paths and local environment. We find faint JWST galaxies (M UV ≳ − 19.5) to remain consistent with the standard galaxy formation model and that our fiducial catalogue includes large samples of their analogues. The properties of these analogues broadly agree with conventional spectral energy distribution-fitting results, except for having systematically lower redshifts due to the evolving ultraviolet luminosity function, and for having higher specific star formation rates as a result of burstier histories in our model. On the other hand, only a handful of bright galaxy analogues can be identified for the observed z ∼ 12 galaxies. Moreover, in order to reproduce the z ≳ 16 JWST galaxy candidates, boosting star-forming efficiencies through reduced feedback regulation and increased gas depletion rate is necessary relative to models of lower redshift populations. This suggests star formation in the first galaxies could differ significantly from their lower redshift counterparts. We also find that these candidates are subject to low-redshift contamination, which is present in our fiducial results as both the dusty or quiescent galaxies at z ∼ 5. [ABSTRACT FROM AUTHOR]

We predict the 21-cm global signal and power spectra during the Epoch of Reionization using the meraxes semi-analytic galaxy formation and reionization model, updated to include X-ray heating and thermal evolution of the intergalactic medium. Studying the formation and evolution of galaxies together with the reionization of cosmic hydrogen using semi-analytic models (such as M  eraxes) requires N -body simulations within large volumes and high-mass resolutions. For this, we use a simulation of side-length 210  h −1 Mpc with 43203 particles resolving dark matter haloes to masses of |$5\times 10^8 \rm{ }h^{-1}\, \mathrm{M_\odot }$|⁠. To reach the mass resolution of atomically cooled galaxies, thought to be the dominant population contributing to reionization, at z  = 20 of |$\sim 2\times 10^7 \text{ }h^{-1}\, \mathrm{M_\odot }$|⁠ , we augment this simulation using the darkforest Monte Carlo merger tree algorithm (achieving an effective particle count of ∼1012). Using this augmented simulation, we explore the impact of mass resolution on the predicted reionization history as well as the impact of X-ray heating on the 21-cm global signal and the 21-cm power spectra. We also explore the cosmic variance of 21-cm statistics within 703  h −3 Mpc3 sub-volumes. We find that the midpoint of reionization varies by Δ z ∼ 0.8 and that the cosmic variance on the power spectrum is underestimated by a factor of 2–4 at k ∼ 0.1–0.4 Mpc−1 due to the non-Gaussian nature of the 21-cm signal. To our knowledge, this work represents the first model of both reionization and galaxy formation which resolves low-mass atomically cooled galaxies while simultaneously sampling sufficiently large scales necessary for exploring the effects of X-rays in the early Universe. [ABSTRACT FROM AUTHOR]

X-rays from high-mass X-ray binaries (HMXBs) are likely the main source of heating of the intergalactic medium (IGM) during Cosmic Dawn (CD), before the completion of reionization. This Epoch of Heating (EoH; z ∼10–15) should soon be detected via the redshifted 21-cm line from neutral hydrogen, allowing us to indirectly study the properties of HMXBs in the unseen, first galaxies. Low-redshift observations, as well as theoretical models, imply that the integrated X-ray luminosity to star formation rate of HMXBs (L X/SFR) should increase in metal-poor environments, typical of early galaxies. Here, we study the impact of the metallicity (Z) dependence of L X/SFR during the EoH. For our fiducial models, galaxies with star formation rates of order 10−3– |$10^{-1}\, M_\odot$| yr−1 and metallicities of order 10−3– |$10^{-2}\, Z_\odot$| are the dominant contributors to the X-ray background (XRB) during this period. Different L X/SFR– Z relations result in factors of ∼ 3 differences in these ranges, as well as in the mean IGM temperature and the large-scale 21-cm power, at a given redshift. We compute mock 21-cm observations adopting as a baseline a 1000 h integration with the upcoming Square Kilometer Array (SKA) for two different L X/SFR– Z relations. We perform inference on these mock observations using the common simplification of a constant L X/SFR, finding that constant L X/SFR models can recover the IGM evolution of the more complicated L X/SFR– Z simulations only during the EoH. At z < 10, where the typical galaxies are more polluted, constant L X/SFR models overpredict the XRB and its relative contribution to the early stages of the reionization. [ABSTRACT FROM AUTHOR]

The formation of the first galaxies during cosmic dawn and reionization (at redshifts z = 5–30), triggered the last major phase transition of our universe, as hydrogen evolved from cold and neutral to hot and ionized. The 21-cm line of neutral hydrogen will soon allow us to map these cosmic milestones and study the galaxies that drove them. To aid in interpreting these observations, we upgrade the publicly available code 21cmFAST. We introduce a new, flexible parametrization of the additive feedback from: an inhomogeneous, H2-dissociating (Lyman–Werner; LW) background; and dark matter – baryon relative velocities; which recovers results from recent, small-scale hydrodynamical simulations with both effects. We perform a large, 'best-guess' simulation as the 2021 installment of the Evolution of 21-cm Structure (EOS) project. This improves the previous release with a galaxy model that reproduces the observed UV luminosity functions (UVLFs), and by including a population of molecular-cooling galaxies. The resulting 21-cm global signal and power spectrum are significantly weaker, primarily due to a more rapid evolution of the star formation rate density required to match the UVLFs. Nevertheless, we forecast high signal-to-noise detections for both HERA and the SKA. We demonstrate how the stellar-to-halo mass relation of the unseen, first galaxies can be inferred from the 21-cm evolution. Finally, we show that the spatial modulation of X-ray heating due to relative velocities provides a unique acoustic signature that is detectable at z ≈ 10–15 in our fiducial model. Ours are the first public simulations with joint inhomogeneous LW and relative-velocity feedback across the entire cosmic dawn and reionization, and we make them available at this link https://scholar.harvard.edu/julianbmunoz/eos-21. [ABSTRACT FROM AUTHOR]

The first generation of galaxies is expected to form in minihaloes, accreting gas through H2 cooling, and possessing unique properties. Although unlikely to be directly detected in UV/infrared surveys, the radiation from these molecular-cooling galaxies (MCGs) could leave an imprint in the 21-cm signal from the Cosmic Dawn. Here, we quantify their detectability with upcoming radio interferometers. We generate mock 21-cm power spectra using a model for both MCGs as well as more massive, atomic-cooling galaxies, allowing both populations to have different properties and scaling relations. The galaxy parameters are chosen so as to be consistent with: (i) high-redshift UV luminosity functions; (ii) the upper limit on the neutral fraction from QSO spectra; (iii) the Thomson scattering optical depth to the CMB; and (iv) the timing of the recent putative EDGES detection. The latter implies a significant contribution of MCGs to the Cosmic Dawn, if confirmed to be cosmological. We then perform Bayesian inference on two models including and ignoring MCG contributions. Comparing their Bayesian evidences, we find a strong preference for the model including MCGs, despite the fact that it has more free parameters. This suggests that if MCGs indeed play a significant role in the Cosmic Dawn, it should be possible to infer their properties from upcoming 21-cm power spectra. Our study illustrates how these observations can discriminate among uncertain galaxy formation models with varying complexities, by maximizing the Bayesian evidence. [ABSTRACT FROM AUTHOR]

The Epoch of Reionization (EoR) depends on the complex astrophysics governing the birth and evolution of the first galaxies and structures in the intergalactic medium. EoR models rely on cosmic microwave background (CMB) observations, and in particular the large-scale E-mode polarization power spectra (EE PS), to help constrain their highly uncertain parameters. However, rather than directly forward-modelling the EE PS, most EoR models are constrained using a summary statistic – the Thompson scattering optical depth, τe. Compressing CMB observations to τe requires adopting a basis set for the EoR history. The common choice is the unphysical, redshift-symmetric hyperbolic tangent (tan h) function, which differs in shape from physical EoR models based on hierarchical structure formation. Combining public EoR and CMB codes, 21 cmfast and class , here we quantify how inference using the τe summary statistic impacts the resulting constraints on galaxy properties and EoR histories. Using the last Planck 2018 data release, we show that the marginalized constraints on the EoR history are more sensitive to the choice of the basis set (tan h versus physical model) than to the CMB likelihood statistic (τe versus PS). For example, EoR histories implied by the growth of structure show a small tail of partial reionization extending to higher redshifts. However, biases in inference using τe are negligible for the Planck 2018 data. Using EoR constraints from high-redshift observations including the quasar dark fraction, galaxy UV luminosity functions, and CMB EE PS, our physical model recovers |$\tau _\mathrm{ e} = 0.0569_{-0.0066}^{+0.0081}$|⁠. [ABSTRACT FROM AUTHOR]

The very first galaxies that started the cosmic dawn likely resided in so-called 'minihaloes', with masses of ∼105– |$10^8{\, {\rm M}_\odot }$|⁠ , accreting their gas from the intergalactic medium through H2 cooling. Such molecularly cooled galaxies (MCGs) mostly formed in pristine environments, hosted massive, metal-free stars, and were eventually sterilized by the build-up of a disassociating (Lyman–Werner; LW) background. Therefore, their properties might be very different from the galaxies we see in the later Universe. Although MCGs are probably too faint to be observed directly, we could nevertheless infer their properties from the imprint they leave in the cosmic 21-cm signal. Here we quantify this imprint by extending the public simulation code 21cmFAST to allow for a distinct population of MCGs. We allow MCGs to have different properties from other galaxies, including unique scaling relations for their stellar-to-halo mass ratios, ionizing escape fractions, and spectral energy distributions. We track inhomogeneous recombinations, disassociative LW feedback, and photoheating from reionization. After demonstrating how MCGs can shape the 21-cm signal, we explore to what extent current observations can already place constraints on their properties. The cosmic microwave background optical depth from Planck sets an upper limit on the product of the ionizing escape fraction and the stellar mass in MCGs. When including also the timing of the putative EDGES absorption signal, we find an additional strong degeneracy between the stellar mass and the X-ray luminosity of MCGs. If proven to be of cosmic origin, the timing of the EDGES signal would have been set by MCGs. [ABSTRACT FROM AUTHOR]

Intergalactic medium temperature is a powerful probe of the epoch of reionization, as information is retained long after reionization itself. However, mean temperatures are highly degenerate with the timing of reionization, with the amount heat injected during the epoch, and with the subsequent cooling rates. We post-process a suite of semi-analytic galaxy formation models to characterize how different thermal statistics of the intergalactic medium can be used to constrain reionization. Temperature is highly correlated with redshift of reionization for a period of time after the gas is heated. However as the gas cools, thermal memory of reionization is lost, and a power-law temperature–density relation is formed, T  = T 0(1 + δ)1 − γ with γ ≈ 1.5. Constraining our model against observations of electron optical depth and temperature at mean density, we find that reionization likely finished at |$z_{\rm {reion}} = 6.8 ^{+ 0.5} _{-0.8}$| with a soft spectral slope of |$\alpha = 2.8 ^{+ 1.2} _{-1.0}$|⁠. By restricting spectral slope to the range [0.5, 2.5] motivated by population II synthesis models, reionization timing is further constrained to |$z_{\rm {reion}} = 6.9 ^{+ 0.4} _{-0.5}$|⁠. We find that, in the future, the degeneracies between reionization timing and background spectrum can be broken using the scatter in temperatures and integrated thermal history. [ABSTRACT FROM AUTHOR]