Search

The optical depth parameterization is typically used to study the 21-cm signals associated with the properties of the neutral hydrogen (H  i) gas and the ionization morphology during the Epoch of Reionization (EoR), without solving the radiative transfer equation. To assess the uncertainties resulting from this simplification, we conduct explicit radiative transfer calculations using the cosmological 21-cm line radiative transfer (C21LRT) code and examine the imprints of ionization structures on the 21-cm spectrum. We consider a globally averaged reionization history and implement fully ionized cavities (H  ii bubbles) of diameters d ranging from 0.01 to 10 Mpc at epochs within the emission and the absorption regimes of the 21-cm global signal. The single-ray C21LRT calculations show that the shape of the imprinted spectral features are primarily determined by d and the 21-cm line profile, which is parametrized by the turbulent velocity of the H  i gas. It reveals the spectral features tied to the transition from ionized to neutral regions that calculations based on the optical depth parametrization were unable to capture. We also present analytical approximations of the calculated spectral features of the H  ii bubbles. The multiple-ray calculations show that the apparent shape of an H  ii bubble (of d  = 5 Mpc at z  = 8), because of the finite speed of light, differs depending on whether the bubble's ionization front is stationary or expanding. Our study shows the necessity of properly accounting for the effects of line-continuum interaction, line broadening, and cosmological expansion to correctly predict the EoR 21-cm signals. [ABSTRACT FROM AUTHOR]

JWST has recently sparked a new era of Lyα spectroscopy, delivering the first measurements of the Lyα escape fraction and velocity profile in typical galaxies at z ≃ 6−10. These observations offer new prospects for insight into the earliest stages of reionization. But to realize this potential, we need robust models of Lyα properties in galaxies at z ≃ 5−6 when the IGM is mostly ionized. Here, we use new JWST observations from the JADES and FRESCO surveys combined with VLT/MUSE and Keck/DEIMOS data to characterize statistical distributions of Lyα velocity offsets, escape fractions, and EWs in z ≃ 5−6 galaxies. We find that galaxies with large Lyα escape fractions (>0.2) are common at z ≃ 5−6, comprising 30 per cent of Lyman break selected samples. Comparing to literature studies, our census suggests that Lyα becomes more prevalent in the galaxy population towards higher redshift from z ∼ 3 to z ∼ 6, although we find that this evolution slows considerably between z ∼ 5 and z ∼ 6, consistent with modest attenuation from residual H i in the mostly ionized IGM at z ≃ 5−6. We find significant evolution in Lyα velocity profiles between z ≃ 2−3 and z ≃ 5−6, likely reflecting the influence of resonant scattering from residual intergalactic H i on the escape of Lyα emission near line centre. This effect will make it challenging to use Lyα peak offsets as a probe of Lyman continuum leakage at z ≃ 5−6. We use our z ≃ 5−6 Lyα distributions to make predictions for typical Lyα properties at z ≳ 8 and discuss implications of a recently discovered Lyα emitter at z ≃ 8.5 with a small peak velocity offset (156 km s−1). [ABSTRACT FROM AUTHOR]

Quasar absorption spectra measurements suggest that reionization proceeded rapidly, ended late at z ∼ 5.5, and was followed by a flat ionizing background evolution. Simulations that reproduce this behaviour often rely on a fine-tuned galaxy ionizing emissivity, which peaks at z ∼ 6–7 and drops a factor of 1.5–2.5 by z ∼ 5. This is puzzling since the abundance of galaxies is observed to grow monotonically during this period. Explanations for this include effects such as dust obscuration of ionizing photon escape and feedback from photoheating of the IGM. We explore the possibility that this drop in emissivity is instead an artefact of one or more modelling deficiencies in reionization simulations. These include possibly incorrect assumptions about the ionizing spectrum and/or inaccurate modelling of IGM clumping. Our results suggest that the need for a drop could be alleviated if simulations are underestimating the IGM opacity from massive, star-forming haloes. Other potential modelling issues either have a small effect or require a steeper drop when remedied. We construct an illustrative model in which the emissivity is nearly flat at reionization's end, evolving only ∼0.05 dex at 5 < z < 7. More realistic scenarios, however, require a ∼0.1–0.3 dex drop. We also study the evolution of the Ly α effective optical depth distribution and compare to recent measurements. We find that models that feature a hard ionizing spectrum and/or are driven by faint, low-bias sources most easily reproduce the mean transmission and optical depth distribution of the forest simultaneously. [ABSTRACT FROM AUTHOR]

We present an analysis of the ultraviolet (UV) continuum slopes (β) for a sample of 172 galaxy candidates at 8 < z phot < 16 selected from a combination of JWST NIRCam imaging and COSMOS/UltraVISTA ground-based near-infrared imaging. Focusing primarily on a new sample of 121 galaxies at 〈 z 〉 ≃ 11 selected from ≃ 320 arcmin2 of public JWST imaging data across 15 independent data sets, we investigate the evolution of β in the galaxy population at z ≥ 9. We find a significant trend between β and redshift, with the inverse-variance weighted mean UV slope evolving from 〈β〉 = −2.17 ± 0.06 at z  = 9.5 to 〈β〉 = −2.59 ± 0.06 at z  = 11.5. Based on a comparison with stellar population models including nebular continuum emission, we find that at z > 10.5 the average UV continuum slope is consistent with the intrinsic blue limit of dust-free stellar populations (βint ≃ −2.6). These results suggest that the moderately dust-reddened galaxy population at z < 10 was essentially unattenuated at z ≃ 11. The extremely blue galaxies being uncovered at z > 10 place important constraints on dust attenuation in galaxies in the early Universe, and imply that the already observed galaxy population is likely supplying an ionizing photon budget capable of maintaining ionized intergalactic medium fractions of ≳ 5 per cent at z ≃ 11. [ABSTRACT FROM AUTHOR]

The early Universe, spanning 400 000 to 400 million years after the big bang (z ≈ 1100–11), has been left largely unexplored as the light from luminous objects is too faint to be observed directly. While new experiments are pushing the redshift limit of direct observations, measurements in the low-frequency radio band promise to probe early star and black hole formation via observations of the hydrogen 21-cm line. In this work, we explore synergies between 21-cm data from the HERA and SARAS 3 experiments and observations of the unresolved radio and X-ray backgrounds using multiwavelength Bayesian analysis. We use the combined data set to constrain properties of Population II and Population III stars as well as early X-ray and radio sources. The joint fit reveals a 68 percentile disfavouring of Population III star formation efficiencies |$\gtrsim 5.7~{{\ \rm per\ cent}}$|⁠. We also show how the 21-cm and the X-ray background data synergistically constrain opposite ends of the X-ray efficiency prior distribution to produce a peak in the 1D posterior of the X-ray luminosity per star formation rate. We find (at 68 per cent confidence) that early galaxies were likely 0.3–318 times as X-ray efficient as present-day starburst galaxies. We also show that the functional posteriors from our joint fit rule out global 21-cm signals deeper than ≲−203 mK and power spectrum amplitudes at k  = 0.34  h  Mpc−1 greater than |$\Delta _{21}^2 \gtrsim 946\ \mathrm{mK}^2$| with 3σ confidence. [ABSTRACT FROM AUTHOR]

The 21-cm hyperfine line of neutral hydrogen is a useful tool to probe the conditions of the Universe during the Dark Ages, Cosmic Dawn, and the Epoch of Reionization. In most of the current calculations, the 21-cm line signals at given frequencies are computed, using an integrated line-of-sight line opacity, with the correction for cosmological expansion. These calculations have not fully captured the line and continuum interactions in the radiative transfer, in response to evolution of the radiation field and the variations of thermal and dynamic properties of the line-of-sight medium. We construct a covariant formulation for the radiative transfer of the 21-cm line and derive the cosmological 21-cm line radiative transfer (C21LRT) equation. The formulation properly accounts for local emission and absorption processes and the interaction between the line and continuum when the radiation propagates across the expanding Universe to the present observer. Our C21LRT calculations show that methods simply summing the line optical depth could lead to error of 5  per cent in the 21-cm signals for redshift z ∼ 12–35 and of |$\gt 10~{{\ \rm per\ cent}}$| for redshift z ≲ 8. Proper covariant radiative transfer is therefore necessary for producing correct theoretical templates for extracting information of the structural evolution of the Universe through the Epoch of Reionization from the 21-cm tomographic data. [ABSTRACT FROM AUTHOR]

Ly α damping wings in the spectra of bright objects at high redshift are a useful probe of the ionization state of the intergalactic medium during the reionization epoch. It has recently been noted that, despite the inhomogeneous nature of reionization, these damping wings have a characteristic shape which is a strong function of the volume-weighted average neutral hydrogen fraction of the intergalactic medium. We present here a closer examination of this finding using a simulation of patchy reionization from the Sherwood–Relics simulation suite. We show that the characteristic shape and scatter of the damping wings are determined by the average neutral hydrogen density along the line of sight, weighted by its contribution to the optical depth producing the damping wing. We find that there is a redshift dependence in the characteristic shape due to the expansion of the Universe. Finally, we show that it is possible to differentiate between the shapes of damping wings in galaxies and young (or faint) quasars at different points in the reionization history at large velocity offsets from the point where the transmission first reaches zero. [ABSTRACT FROM AUTHOR]

Cosmological simulations serve as invaluable tools for understanding the Universe. However, the technical complexity and substantial computational resources required to generate such simulations often limit their accessibility within the broader research community. Notable exceptions exist, but most are not suited for simultaneously studying the physics of galaxy formation and cosmic reionization during the first billion years of cosmic history. This is especially relevant now that a fleet of advanced observatories (e.g. James Webb Space Telescope, Nancy Grace Roman Space Telescope , SPHEREx, ELT, SKA) will soon provide an holistic picture of this defining epoch. To bridge this gap, we publicly release all simulation outputs and post-processing products generated within the thesan simulation project at www.thesan-project.com. This project focuses on the z ≥ 5.5 Universe, combining a radiation-hydrodynamics solver (arepo-rt), a well-tested galaxy formation model (IllustrisTNG) and cosmic dust physics to provide a comprehensive view of the Epoch of Reionization. The thesan suite includes 16 distinct simulations, each varying in volume, resolution, and underlying physical models. This paper outlines the unique features of these new simulations, the production and detailed format of the wide range of derived data products, and the process for data retrieval. Finally, as a case study, we compare our simulation data with a number of recent observations from the James Webb Space Telescope , affirming the accuracy and applicability of thesan. The examples also serve as prototypes for how to utilize the released data set to perform comparisons between predictions and observations. [ABSTRACT FROM AUTHOR]

Recent measurements of the ionizing photon mean free path (MFP) based on composite quasar spectra may point to reionization ending at z < 6. These measurements are challenging because they rely on assumptions about the proximity zones of the quasars. For example, some quasars might have been close to neutral patches where reionization was still ongoing ('neutral islands'), and it is unclear how they would affect the measurements. We address this question with mock MFP measurements from radiative transfer simulations. We find that, even in the presence of neutral islands, our mock MFP measurements agree to within |$30~{{\ \rm per\ cent}}$| with the true spatially averaged MFP in our simulations, which includes opacity from both the ionized medium and the islands. The inferred MFP is sensitive at the |$\lt ~50~{{\ \rm per\ cent}}$| level to assumptions about quasar environments and lifetimes for realistic models. We demonstrate that future analyses with improved data may require explicitly modelling the effects of neutral islands on the composite spectra, and we outline a method for doing this. Lastly, we quantify the effects of neutral islands on Lyman-series transmission, which has been modelled with optically thin simulations in previous MFP analyses. Neutral islands can suppress transmission at λrest < 912 Å significantly, up to a factor of 2 for z qso = 6 in a plausible reionization scenario, owing to absorption by many closely spaced lines as quasar light redshifts into resonance. However, the suppression is almost entirely degenerate with the spectrum normalization and thus does not significantly bias the inferred MFP. [ABSTRACT FROM AUTHOR]

The observation of the global 21 cm signal produced by neutral hydrogen gas in the intergalactic medium (IGM) during the Dark Ages, Cosmic Dawn, and Epoch of Reionization requires measurements with extremely well-calibrated wideband radiometers. We describe the design and characterization of the Mapper of the IGM Spin Temperature (MIST), which is a new ground-based, single-antenna, global 21 cm experiment. The design of MIST was guided by the objectives of avoiding systematics from an antenna ground plane and cables around the antenna, as well as maximizing the instrument's on-sky efficiency and portability for operations at remote sites. We have built two MIST instruments, which observe in the range 25–105 MHz. For the 21 cm signal, this frequency range approximately corresponds to redshifts 55.5 > z > 12.5, encompassing the Dark Ages and Cosmic Dawn. The MIST antenna is a horizontal blade dipole of 2.42 m in length, 60 cm in width, and 52 cm in height above the ground. This antenna operates without a metal ground plane. The instruments run on 12 V batteries and have a maximum power consumption of 17 W. The batteries and electronics are contained in a single receiver box located under the antenna. We present the characterization of the instruments using electromagnetic simulations and lab measurements. We also show sample sky measurements from recent observations at remote sites in California, Nevada, and the Canadian High Arctic. These measurements indicate that the instruments perform as expected. Detailed analyses of the sky measurements are left for future work. [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]

We present a Bayesian inference on the neutral hydrogen fraction of the intergalactic medium (IGM), x small HI, at z ∼6-8 using the properties of Lyman break galaxies (LBGs) during the epoch of reionization. We use large samples of LBG candidates at 5.5 ≤ z ≤ 8.2 with spectroscopy from Keck/DEIMOS and Keck/MOSFIRE. For each galaxy, we incorporate either the Lyman-α (Lyα) equivalent width (EW) for detections or the EW limit spectrum for non-detections to parametrize the EW distribution at various ultraviolet brightnesses for a given redshift. Using our reference sample of galaxy candidates from the ionized universe at z ∼6.0, we are able to infer x small HI at two redshifts: z ∼6.7 and z ∼7.6. This work includes intrinsically faint, gravitationally lensed galaxies at z ∼6.0 in order to constrain the intrinsic faint-end Lyα EW distribution and provide a comparable population of galaxies to counterparts in our sample that are at higher redshift. The inclusion of faint galaxy candidates, in addition to a more sophisticated modelling framework, allows us to better isolate effects of the interstellar medium and circumgalactic medium on the observed Lyα distribution from those of the IGM. We infer an upper limit of x small HI ≤ 0.25 (0.44) at z = 6.7 ± 0.2 and a neutral fraction of x small HI = 0.83+0.08 -0.11 (0.83 +0.11 -0.21) at z = 7.6 ± 0.6, both within 68 per cent (95 per cent) uncertainty, results that favour a moderately late and fairly rapid reionization.

Early JWST observations that targeted so-called double-break sources (attributed to Lyman and Balmer breaks at z > 7), reported a previously unknown population of very massive, evolved high-redshift galaxies. This surprising discovery led to a flurry of attempts to explain these objects' unexpected existence including invoking alternatives to the standard Λ cold dark matter (ΛCDM) cosmological paradigm. To test these early results, we adopted the same double-break candidate galaxy selection criteria to search for such objects in the JWST images of the CAnadian Near Infrared Imager and Slitless Spectrograph (NIRISS) Unbiased Cluster Survey (CANUCS), and found a sample of 19 sources over five independent CANUCS fields that cover a total effective area of ∼60 arcmin2 at z ∼ 8. However, (1) our spectral energy distribution fits do not yield exceptionally high-stellar masses for our candidates, while (2) spectroscopy of five of the candidates shows that while all five are at high redshifts, their red colours are due to high-equivalent width emission lines in star-forming galaxies rather than Balmer breaks in massive, evolved systems. Additionally, (3) field-to-field variance leads to differences of ∼1.5 dex in the maximum stellar masses measured in the different fields, suggesting that the early single-field JWST observations may have suffered from cosmic variance and/or sample bias. Finally, (4) we show that the presence of even a single massive outlier can dominate conclusions from small samples such as those in early JWST observations. In conclusion, we find that the double-break sources in CANUCS are not sufficiently massive or numerous to warrant questioning the standard ΛCDM paradigm. [ABSTRACT FROM AUTHOR]

The attenuation of Lyα photons by neutral hydrogen in the intergalactic medium (IGM) at z ≳ 5 continues to be a powerful probe for studying the epoch of reionization. Given a framework to estimate the intrinsic (true) Lyα emission of high- z sources, one can infer the ionization state of the IGM during reionization. In this work, we use the enlarged XQR-30 sample of 42 high-resolution and high signal-to-noise quasar spectra between |$5.8\lesssim \, z\lesssim \, 6.6$| obtained with VLT/X-shooter to place constraints on the IGM neutral fraction. This is achieved using our existing Bayesian QSO reconstruction framework which accounts for uncertainties such as the: (i) posterior distribution of predicted intrinsic Lyα emission profiles (obtained via covariance matrix reconstruction of the Lyα and N  v emission lines from unattenuated high-ionization emission line profiles; C  iv , Si  iv   + O  iv ], and C  iii ]) and (ii) distribution of ionized regions within the IGM using synthetic damping wing profiles drawn from a 1.63 Gpc3 reionization simulation. Following careful quality control, we used 23 of the 42 available QSOs to obtain constraints/limits on the IGM neutral fraction during the tail-end of reionization. Our median and 68th percentile constraints on the IGM neutral fraction are: |$0.20\substack{+0.14 -0.12}$| and |$0.29\substack{+0.14 -0.13}$| at z  = 6.15 and 6.35. Further, we also report 68th percentile upper limits of |$\bar{x}_{\mathrm{H\, {\small I}}{}} \lt 0.21$|⁠ , 0.20, 0.21, and 0.18 at z  = 5.8, 5.95, 6.05, and 6.55. These results imply reionization is still ongoing at |$5.8\lesssim \, z\lesssim \, 6.55$|⁠ , consistent with previous results from XQR-30 (dark fraction and Lyα forest) along with other observational probes considered in the literature. [ABSTRACT FROM AUTHOR]

The early stages of the epoch of reionization, probed by the 21 cm line, are sensitive to the detailed properties and formation histories of the first galaxies. We use 21cmfast and a simple, self-consistent galaxy model to examine the redshift evolution of the large-scale cross-power spectrum between the 21 cm field and line-emitting galaxies. A key transition in redshift occurs when the 21 cm field shifts from being positively correlated with the galaxy distribution to being negatively correlated. Importantly, this transition redshift is insensitive to the properties of the galaxy tracers but depends sensitively on the thermal and ionization histories traced through the 21 cm field. Specifically, we show that the transition occurs when both ionization fluctuations dominate over 21 cm spin temperature fluctuations and when the average spin temperature exceeds the temperature of the cosmic microwave background. We illustrate this with three different 21 cm models which have largely the same neutral fraction evolution but different heating histories. We find that the transition redshift has a scale dependence, and that this can help disentangle the relative importance of heating and ionization fluctuations. The best prospects for constraining the transition redshift occur in scenarios with late X-ray heating, where the transition occurs at redshifts as low as z ∼ 6–8. In our models, this requires high-redshift galaxy surveys with sensitivities of |$\sim 10^{-18}~\rm erg\,s^{-1}\,cm^{-2}$| for optical lines and |$\sim 10^{-19}~\rm erg\,s^{-1}\,cm^{-2}$| for far-infrared lines. Future measurements of the transition redshift can help discriminate between 21 cm models and will benefit from reduced systematics. [ABSTRACT FROM AUTHOR]

The hydrogen 21-cm signal is predicted to be the richest probe of the young Universe, including those eras known as the cosmic Dark Ages, the Cosmic Dawn (when the first star and black hole formed) and the Epoch of Reionization. This signal holds the key to deciphering processes that take place at the early stages of cosmic history. In this opinion piece, we discuss the potential scientific merit of lunar observations of the 21-cm signal and their advantages over more affordable terrestrial efforts. The Moon is a prime location for radio cosmology which will enable precision observations of the low-frequency radio sky. The uniqueness of such observations is that they will provide an unparalleled opportunity to test cosmology and the nature of dark matter using the Dark Ages 21-cm signal. No less enticing is the opportunity to obtain a much clearer picture of the Cosmic Dawn than that currently achievable from the ground, which will allow us to determine the properties of the first stars and black holes. This article is part of a discussion meeting issue 'Astronomy from the Moon: the next decades (part 2)'. [ABSTRACT FROM AUTHOR]

Context. Halos with masses in excess of the atomic limit are believed to be ideal environments in which to form heavy black hole seeds with masses above 103 M⊙. In cases where the H2 fraction is suppressed, this is expected to lead to reduced fragmentation of the gas and the generation of a top-heavy initial mass function. In extreme cases this can result in the formation of massive black hole seeds. Resolving the initial fragmentation scale and the resulting protostellar masses has, until now, not been robustly tested. Aims. We run zoom-in simulations of atomically cooled halos in which the formation of H2 is suppressed to assess whether they can truly resist fragmentation at high densities and tilt the initial mass function towards a more top-heavy form and the formation of massive black hole seeds. Methods. Cosmological simulations were performed with the moving mesh code AREPO, using a primordial chemistry network until z ∼ 11. Three haloes with masses in excess of the atomic cooling mass were then selected for detailed examination via zoom-ins. A series of zoom-in simulations, with varying levels of maximum spatial resolution, captured the resulting fragmentation and formation of metal-free stars using the sink particle technique. The highest resolution simulations resolved densities up to 10−6 g cm−3 (1018 cm−3) and captured a further 100 yr of fragmentation behaviour at the centre of the halo. Lower resolution simulations were then used to model the future accretion behaviour of the sinks over longer timescales. Results. Our simulations show intense fragmentation in the central region of the halos, leading to a large number of near-solar mass protostars. Even in the presence of a super-critical Lyman-Werner radiation field (JLW > 105J21), H2 continues to form within the inner ∼2000 au of the halo. Despite the increased fragmentation, the halos produce a protostellar mass spectrum that peaks at higher masses relative to standard Population III star-forming halos. The most massive protostars have accretion rates of 10−3–10−1 M⊙ yr−1 after the first 100 years of evolution, while the total mass of the central region grows at 1 M⊙ yr−1. Lower resolution zoom-ins show that the total mass of the system continues to accrete at ∼1 M⊙ yr−1 for at least 104 yr, although how this mass is distributed amongst the rapidly growing number of protostars is unclear. However, assuming that a fraction of stars can continue to accrete rapidly, the formation of a sub-population of stars with masses in excess of 103 M⊙ is likely in these halos. In the most optimistic case, we predict the formation of heavy black hole seeds with masses in excess of 104 M⊙, assuming an accretion behaviour in line with expectations from super-competitive accretion and/or frequent mergers with secondary protostars. [ABSTRACT FROM AUTHOR]

Context. Population III (pop III) stars were born in halos characterised by a pristine gas composition. In such a halo, once the gas density reaches nH ∼ 1 cm−3, molecular cooling leads to the collapse of the gas and the birth of pop III stars. Halo properties, such as the chemical abundances, mass, and angular momentum can affect the collapse of the gas, thereby leading to the pop III initial mass function (IMF) of star formation. Aims. We want to study the properties of primordial halos and how halos that host early star formation differ from other types of halos. The aim of this study is to obtain a representative population of halos at a given redshift hosting a cold and massive gas cloud that enables the birth of the first stars. Methods. We investigated the growth of primordial halos in a ΛCDM Universe in a large cosmological simulation. We used the hydrodynamic code RAMSES and the chemical solver KROME to study halo formation with non-equilibrium thermochemistry. We then identified structures in the dark and baryonic matter fields, thereby linking the presence or absence of dense gas clouds to the mass and the physical properties of the hosting halos. Results. In our simulations, the mass threshold for a halo for hosting a cold dense gas cloud is ≃7 × 105 M⊙ and the threshold in the H2 mass fraction is found to be ≃2 × 10−4. This is in agreement with previous works. We find that the halo history and accretion rate play a minor role. Here, we present halos with higher HD abundances, which are shown to be colder, as the temperature in the range between 102 − 104 cm−3 depends on the HD abundance to a large extent. The higher fraction of HD is linked to the higher spin parameter that is seen for the dense gas. [ABSTRACT FROM AUTHOR]

The spatial fluctuations in the tomographic maps of the redshifted 21-cm signal from the Cosmic Dawn (CD) crucially depend on the size and distribution of the regions with gas temperatures larger than the radio background temperature. In this article, we study the morphological characteristics of such emission regions and their absorption counterparts using the shape diagnostic tool surfgen2. Using simulated CD brightness temperature cubes of the 21-cm signal, we find that the emission regions percolate at stages with the filling factor of the emission regions |$\mathrm{FF}_{\rm emi}\gtrsim 0.15$|⁠. Percolation of the absorption regions occurs for |$\mathrm{FF}_{\rm abs}\gtrsim 0.05$|⁠. The largest emission and absorption regions are topologically complex and highly filamentary for most parts of the CD. The number density of these regions as a function of the volume shows the power-law nature with the power-law indexes |$\approx -2$| and |$-1.6$| for the emission and absorption regions, respectively. Overall, the planarity, filamentarity, and genus increase with the increase of the volume of both emission and absorption regions. [ABSTRACT FROM AUTHOR]

The patchiness in the reionization process alters the statistics of cosmic microwave background (CMB), with the kinematic Sunyaev–Zeldovich (kSZ) effect in the CMB temperature power spectrum being a notable consequence. In this work, we aim to explore the potential of future kSZ power spectrum measurements in inferring the details of the reionization process. In this pursuit, we capitalize on the recent developments in foreground mitigation techniques using the Cross-Internal Linear Combination (Cross-ILC) technique, which enables robust detection of the kSZ power spectrum with signal-to-noise ratio roughly 20σ–30σ in this decade by South pole Telescope (SPT-3G) and Simons Observatory (SO); and ≥80σ by CMB-S4 – substantially improving on the recent evidence for kSZ binned at ℓ = 3000 using SPT-SZ + SPTpol surveys. We use a fiducial kSZ power spectrum along with realistic error bars expected from the above technique for SPT-3G, SO, and CMB-S4 to constrain the parameter space for a physical model of reionization. We find that with the improved error bars it will be possible to place stringent constraints on reionization using solely the Cross-ILC recovered SPT-3G kSZ without imposing any prior on τ in the Bayesian inference. Notably, high-fidelity kSZ measurements from CMB-S4 coupled with τ measurements through LiteBIRD will enable unprecedented constraint on the midpoint of reionization with an error bar of ∼0.25 and the duration of reionization with an error bar at ∼0.21 exclusively using CMB data. This study highlights the need to capture kSZ power spectrum on a broad range of multipoles to gain insights into the inhomogeneous reionization era. [ABSTRACT FROM AUTHOR]

The 21-cm line emitted by neutral hydrogen is the most promising probe of the Epoch of Reionization (EoR). Multiple radio interferometric instruments are on the cusp of detecting its power spectrum. It is therefore essential to deliver robust theoretical predictions, enabling sound inference of the coeval Universe properties. The nature of this signal traditionally required the modelling of |$\mathcal {O}(10^{7-8} \, {\rm Mpc}^3)$| volumes to suppress the impact of cosmic variance. However, the recently proposed Fixed & Paired (F&P) approach uses carefully crafted simulation pairs to achieve equal results in smaller volumes. In this work, we thoroughly test the applicability of and improvement granted by this technique to different observables of the 21-cm signal from the EoR. We employ radiation-magneto-hydrodynamics simulations to ensure the most realistic physical description of this epoch, greatly improving over previous studies using a seminumerical approach without accurate galaxy formation physics and radiative transfer. We estimate the statistical improvement granted by the F&P technique on predictions of the skewness, power spectrum, bispectrum, and ionized regions size distribution of the 21-cm signal at redshift 7 ≤ z ≤ 10 (corresponding to |${\ge}80{{\ \rm per\ cent}}$| of the gas being neutral). We find that the effective volume of F&P simulations is at least 3.5 times larger than traditional simulations. This directly translates into an equal improvement in the computational cost (in terms of time and memory). Finally, we confirm that a combination of different observables like skewness, power spectrum, and bispectrum across different redshifts can be utilized to maximize the improvement. [ABSTRACT FROM AUTHOR]

Reliable indirect diagnostics of LyC photon escape from galaxies are required to understand which sources were the dominant contributors to reionization. While multiple LyC escape fraction (f esc) indicators have been proposed to trace favourable conditions for LyC leakage from the interstellar medium of low-redshift 'analogue' galaxies, it remains unclear whether these are applicable at high redshifts where LyC emission cannot be directly observed. Using a library of 14 120 mock spectra of star-forming galaxies with redshifts 4.64 ≤ z ≤ 10 from the SPHINX20 cosmological radiation hydrodynamics simulation, we develop a framework for the physics that leads to high f esc. We investigate LyC leakage from our galaxies based on the criteria that successful LyC escape diagnostics must (i) track a high-specific star formation rate, (ii) be sensitive to stellar population age in the range 3.5–10 Myr representing the times when supernova first explode to when LyC production significantly drops, and (iii) include a proxy for neutral gas content and gas density in the interstellar medium. O32, ΣSFR, MUV, and H β equivalent width select for one or fewer of our criteria, rendering them either necessary but insufficient or generally poor diagnostics. In contrast, UV slope (β), and E (B − V) match two or more of our criteria, rendering them good f esc diagnostics (albeit with significant scatter). Using our library, we build a quantitative model for predicting f esc based on direct observables. When applied to bright z > 6 Ly α emitters observed with JWST, we find that the majority of them have |$f_{\rm esc} \lesssim 10~{{\ \rm per\ cent}}$|⁠. [ABSTRACT FROM AUTHOR]

Upcoming experiments will map the spatial distribution of the 21-cm signal over three-dimensional volumes of space during the Epoch of Reionization (EoR). Several methods have been proposed to mitigate the issue of astrophysical foreground contamination in tomographic images of the 21-cm signal, one of which involves the excision of a wedge-shaped region in cylindrical Fourier space. While this removes the k -modes most readily contaminated by foregrounds, the concurrent removal of cosmological information located within the wedge considerably distorts the structure of 21-cm images. In this study, we build upon a U-Net-based deep-learning algorithm to reconstruct foreground wedge-removed maps of the 21-cm signal, newly incorporating light-cone effects. Adopting the Square Kilometre Array as our fiducial instrument, we highlight that our U-Net recovery framework retains a reasonable level of reliability even in the face of instrumental limitations and noise. We subsequently evaluate the efficacy of recovered maps in guiding high-redshift galaxy searches and providing context to existing galaxy catalogues. This will allow for studies of how the high-redshift galaxy luminosity function varies across environments, and ultimately refine our understanding of the connection between the ionization state of the intergalactic medium and galaxies during the EoR. [ABSTRACT FROM AUTHOR]

X-ray photons can penetrate deep into the intergalactic medium (IGM), leading to pre-heating of the IGM prior to cosmic reionization. X-ray pre-heating wipes out some of the small-scale structures that would otherwise be present prior to the passage of an ionization front. Accurate modelling of the small-scale structure is vital to the post-reionization IGM, since the small-scale structure is ultimately the dominant source of long-lasting relics from hydrogen reionization. However, the precise impact of X-ray pre-heating in the fossils from hydrogen reionization is highly uncertain. In this work, we explore and establish for the first time, the long-lasting impact of X-ray pre-heating in the post-reionization IGM via hydrodynamic simulations with high-mass resolution. We find that the addition of X-ray pre-heating astrophysics leads to an overall lesser impact of the effect of inhomogeneous reionization in the Lyα forest – depending on specific X-ray prescription – at low redshifts (z ∼ 2) with respect to a model with no X-ray pre-heating. However, at high redshifts (z ∼ 4), our results indicate a strengthening of the relics of reionization in the Lyα forest because the IGM becomes more transparent compared to the scenario with no pre-heating. Thus, the absence of X-ray pre-heating in Lyα modelling can lead to a biased inference of cosmological parameters. Nevertheless, optimistically, the inclusion of X-ray pre-heating emerges as a promising novel avenue to probe the astrophysics of cosmic dawn. [ABSTRACT FROM AUTHOR]

We use the Cosmic Archaeology Tool (CAT) semi-analytical model to explore the contribution of Population (Pop) III/II stars and active galactic nuclei (AGNs) to the galaxy ultraviolet (UV) luminosity function (LF) evolution at 4 ≤ z ≤ 20. We compare in particular with recent JWST data in order to explore the apparent tension between observations and theoretical models in the number density of bright galaxies at z ≳ 10. The model predicts a star formation history dominated by UV faint (M UV > −18) galaxies, with a Pop III contribution of |$\lesssim 10~{{\ \rm per\ cent}}$| (⁠|$\lesssim 0.5~{{\ \rm per\ cent}}$|⁠) at z ≃ 20 (z ≃ 10). Stars are the primary sources of cosmic reionization, with |$5~{{\ \rm per\ cent}}\!-\!10~{{\ \rm per\ cent}}$| of ionizing photons escaping into the intergalatic medium at 5 ≤ z ≤ 10, while the contribution of unobscured AGNs becomes dominant only at z ≲ 5. The predicted stellar and AGN UV LFs reproduce the observational data at 5 ≲ z ≲ 9–10. At higher redshift, CAT predicts a steeper evolution in the faint-end slope (M UV > –18), and a number density of bright galaxies (M UV ≃ −20) consistent with data at z ∼ 10–11, but smaller by 0.8 dex at z ∼ 12–13, and 1.2 dex at z ∼ 14–16, when compared to the values estimated by recent studies. Including the AGN emission does not affect the above findings, as AGNs contribute at most to |$\lesssim 10~{{\ \rm per\ cent}}$| of the total UV luminosity at M UV < –19 and z ≳ 10. Interestingly, considering a gradual transition in the stellar initial mass function, modulated by metallicity and redshift as suggested by recent simulations, the model agrees with JWST data at z ∼ 12–13, and the disagreement at z ∼ 14–16 is reduced to 0.5 dex. [ABSTRACT FROM AUTHOR]

Foreground removal is one of the biggest challenges in the detection of the Cosmic Dawn (CD) and Epoch of Reionization (EoR). Various foreground subtraction techniques have been developed based on the spectral smoothness of foregrounds. However, the sources with a spectral peak (SP) at megahertz may break down the spectral smoothness at low frequencies (<1000 MHz). In this paper, we cross-match the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) extragalactic source catalogue with three other radio source catalogues, covering the frequency range 72 MHz–1.4 GHz, to search for sources with spectral turnover. 4423 sources from the GLEAM catalogue are identified as SP sources, representing ≈3.2 per cent of the GLEAM radio source population. We utilize the properties of SP source candidates obtained from real observations to establish simulations and test the impact of SP sources on the extraction of CD/EoR signals. We statistically compare the differences introduced by SP sources in the residuals after removing the foregrounds with three methods, which are polynomial fitting, principal component analysis, and fast independent component analysis. Our results indicate that the presence of SP sources in the foregrounds has a negligible influence on extracting the CD/EoR signal. After foreground subtraction, the contribution from SP sources to the total power in the two-dimensional power spectrum within the EoR window is approximately 3–4 orders of magnitude lower than the CD/EoR signal. [ABSTRACT FROM AUTHOR]

The cosmological 21-cm signal offers a potential probe of the early Universe and the first ionizing sources. Current experiments probe the spatially dependent variance (Gaussianity) of the signal through the power spectrum (PS). The signal, however, is expected to be highly non-Gaussian due to the complex topology of reionization and X-ray heating. We investigate the non-Gaussianities of X-ray heating and reionization, by calculating the skew spectrum (SS) of the 21-cm signal using meraxes , which couples a semi-analytic galaxy population with seminumerical reionization simulations. The SS is the cross-spectrum of the quadratic temperature brightness field with itself. We generate a set of seven simulations from z = 30 to 5, varying the halo mass threshold for hosting star formation, the X-ray luminosity per star formation rate, and the minimum X-ray energy escaping host galaxies. We find the SS is predominantly negative as a function of redshift, transitioning to positive towards the start of reionization, and peaking during the mid-point of reionization. We do not see a negative dip in the SS during reionization, likely due to the specifics of modelling ionization sources. We normalize the SS by the PS during reionization isolating the non-Gaussianities. We find a trough (⁠|$k\sim \, 0.1\, \textrm {Mpc}^{-1}$|⁠) and peak (⁠|$k\sim \, 0.4{-}1\, \textrm {Mpc}^{-1}$|⁠) in the normalized SS during the mid-to-late periods of reionization. These correlate to the ionization topology, and neutral islands in the IGM. We calculate the cosmic variance of the normalized SS, and find these features are detectable in the absence of foregrounds with the SKA_LOW. [ABSTRACT FROM AUTHOR]

This document is a correction to a previous article titled "Recovering the wedge modes lost to 21-cm foregrounds" published in the Monthly Notices of the Royal Astronomical Society. The correction addresses an issue with the training and validation sets used to train a neural network in the original article. The overlap of random seeds between the sets resulted in overfitting and affected the conclusions of the original study. The correction proposes adjustments to the neural network and presents new performance statistics and sample predictions. Despite the flaw in the original treatment of the data, the correction confirms the validity of the approach and the main message of the original article. The data and codes mentioned in the correction are available upon request. [Extracted from the article]

Global 21-cm experiments are built to study the evolution of the Universe between the cosmic dawn and the epoch of reionization. FlexKnot is a function parametrized by freely moving knots stringed together by splines. Adopting the FlexKnot function as the signal model has the potential to separate the global 21-cm signal from the foregrounds and systematics while being capable of recovering the crucial features given by theoretical predictions. In this paper, we implement the FlexKnot method by integrating twice over a function of freely moving knots interpolated linearly. The function is also constrained at the lower frequencies corresponding to the dark ages by theoretical values. The FlexKnot model is tested in the framework of the realistic data analysis pipeline of the REACH global signal experiment using simulated antenna temperature data. We demonstrate that the FlexKnot model performs better than existing signal models, e.g. the Gaussian signal model, at reconstructing the shape of the true signals present in the simulated REACH data, especially for injected signals with complex structures. The capabilities of the FlexKnot signal model is also tested by introducing various systematics and simulated global signals of different types. These tests show that four to five knots are sufficient to recover the general shape of most realistic injected signals, with or without sinusoidal systematics. We show that true signals whose absorption trough is of amplitude between 120 and 450 mK can be well recovered with systematics up to about 50 mK. [ABSTRACT FROM AUTHOR]

Several studies have detected Lyman-alpha (Ly  α) from bright (⁠|$M_{\small UV}\lesssim -21.5$|⁠) galaxies during the early stages of reionization despite the significantly neutral intergalactic medium. To explain these detections, it has been suggested that z > 7 Ly  α emitters (LAEs) inhabit physical Mpc (pMpc)-scale ionized regions powered by overdensities of faint galaxies; however, systematic searches for these overdensities near LAEs have been challenging. Here, we use Cosmic Evolution Early Release Science JWST /Near Infrared Camera imaging to search for large-scale galaxy overdensities near two very ultraviolet (UV)-bright, z  = 8.7 LAEs in the Extended Groth Strip (EGS) field. We colour select 27 z  = 8.4–9.1 candidates, including the one LAE in the footprint (EGSY8p7). From spectral energy distribution models, we infer moderately faint UV luminosities (⁠|$-21.2\lesssim {M_{\small UV}}\lesssim -19.1$|⁠) and stellar masses of M * ≈ 107.5–8.8 M⊙. All are efficient ionizing agents (⁠|$\xi _{\text{ion}}^{*}\approx 10^{25.5-26.0}$| Hz erg−1) and are generally morphologically simple with only one compact (re ≲ 140 to ∼650 pc) star-forming component. 13 candidates lie within 5 arcmin of EGSY8p7, leading to a factor-of-four galaxy overdensity at ≲5 arcmin (∼1.4 projected pMpc at z ∼ 8.7) separations from EGSY8p7. Separations of 10–15 arcmin (∼2.7–4.1 projected pMpc) are consistent with an average field. The spatial distribution of our sample may qualitatively suggest an R ≥ 2 pMpc ionized bubble encompassing both LAEs in EGS, which is theoretically unexpected but may be possible for a galaxy population four times more numerous than the average to create with moderate escape fractions (f esc ≳ 0.15) over long times (≳ 200 Myr). Upcoming spectroscopic follow-up will characterize the size of any ionized bubble that may exist and the properties of the galaxies powering such a bubble. [ABSTRACT FROM AUTHOR]

Constraints on the potential properties of superconducting cosmic strings provide an indirect probe of physics beyond the standard model at energies inaccessible to terrestrial particle colliders. In this study, we perform the first joint Bayesian analysis to extract constraints on superconducting cosmic strings from current 21-cm signal measurements while accounting rigorously for the uncertainties in foregrounds and high redshift astrophysics. We include the latest publicly available 21-cm power spectrum upper limits from HERA, 21-cm global signal data from SARAS 3, and the synergistic probe of the unresolved X-ray background in our final analysis. This paper thus constitutes the first attempt to use 21-cm power spectrum data to probe cosmic strings. In contrast to previous works, we find no strong constraints can be placed on superconducting cosmic strings from current 21-cm measurements. This is because of uncertainties in the X-ray emission efficiency of the first galaxies, with X-ray emissivities greater than 3 × 1040 erg s−1 M |$_{\odot }^{-1}$|  yr able to mask the presence of cosmic strings in the 21-cm signal. We conclude by discussing the prospects for future constraints from definitive 21-cm signal measurements and argue that the recently proposed soft photon heating should be cause for optimism due to its potential to break degeneracies that would have otherwise made the signatures of cosmic strings difficult to distinguish from those of astrophysical origin. [ABSTRACT FROM AUTHOR]

We compare the performance of the popular Bondi–Hoyle–Lyttleton accretion scheme with a simple mass-flux scheme applied to stellar-mass black holes (BHs) across six levels of increasing spatial resolution. Simulating the formation of BHs within cosmological mini-haloes at z ∼ 20, we investigate scenarios both with and without supernova events, which result in BHs of initial mass |$10.8$| and |$270 \, {\rm M_\odot }$|⁠ , respectively. Our explicit focus on the stellar-mass range pushes the maximum resolution down to sub- |$10^{-3} \, {\rm pc}$| regimes, where more complicated gas dynamics are resolved. We observe efficient growth and rotationally supported, |${\sim }10^{-1} \, {\rm pc}$| -scale discs around all |$270 \, {\rm M_\odot }$| BHs independent of resolution and accretion scheme, though clumps, bars, and spiral arm structures impact stability at high resolution. We analyse the effect of these instabilities on the accretion cycle. In contrast, all bar one of the |$10.8 \, {\rm M_\odot }$| BHs fail to attract a disc and experience modest growth, even when characteristic scales of accretion and dynamical friction are reasonably resolved. While the two accretion schemes somewhat converge in mass growth for the |$270 \, {\rm M_\odot }$| case over |$1 \, {\rm Myr}$|⁠ , the greater degree of gas fragmentation induces more randomness in the evolution of the |$10.8 \, {\rm M_\odot }$| BHs. We conclude that early universe BHs of |$M_{\rm BH} \sim 10^1 \, {\rm M_\odot }$| struggle to grow even in gas-rich environments without feedback in comparison to seeds of |$M_{\rm BH} \sim 10^2 \, {\rm M_\odot }$|⁠ , and the latter exhibit convergent growth histories across accretion schemes below a resolution of |$\mathrm{ d}x = 1 \times 10^{-3} \, {\rm pc}$|⁠. [ABSTRACT FROM AUTHOR]

Spatial variations in the Lyman-α forest opacity at z < 6 seem to require a late end to cosmic reionization. In this picture, the Universe contains neutral hydrogen 'islands' of up to 100 cMpc/ h in extent down to redshifts as low as z ∼ 5.3. This delayed end to reionization also seems to be corroborated by various other observables. An implication of this scenario is that the power spectrum of the cosmological 21-cm signal at z < 6 is enhanced relative to conventional reionization models by orders of magnitude. However, these neutral hydrogen islands are also predicted to be at the locations of the deepest voids in the cosmological large-scale structure. As a result, the distribution of the 21-cm signal from them is highly non-Gaussian. We derive the 21-cm bispectrum signal from these regions using high-dynamic-range radiative transfer simulations of reionization. We find that relative to conventional models in which reionization is complete at z > 6, our model has a significantly larger value of the 21-cm bispectrum. The neutral islands also imprint a feature in the isosceles bispectrum at a characteristic scale of ∼1 cMpc−1. We also study the 21-cm bispectrum for general triangle configuration by defining a triangle index. It should be possible to detect the 21-cm bispectrum signal at ν ≳ 200 MHz using SKA1-LOW for 1080 h of observation, assuming optimistic foreground removal. [ABSTRACT FROM AUTHOR]

Outward migration of massive binary stars or black holes in their circumbinary disc is often observed in simulations and it is key to the formation of wide black hole binaries. Using numerical simulations of Population III (Pop III) star formation, we study the angular momentum of Pop III binaries and the torques between stars and gas discs to understand the origin of outward migration and high ellipticity. The outward migration of protostars is produced by gravitational torques exerted on them by their circumstellar minidiscs. The minidiscs, on the other hand, migrate outward mainly by gaining angular momentum by accreting gas from the circumbinary disc. The angular momentum transfer is most efficient for rapidly accreting equal-mass binaries, and weaker when the secondary mass is small or the massive companion evaporates the gas disc via radiative feedback. We conclude that outward migration and the formation of wide equal-mass massive binaries is common in metal-free/metal-poor star formation, mainly driven by their large accretion rates. We expect that the lower gas temperature and accretion rates in metal-enriched circumstellar discs would lead more often to inward migration and closer binary separations. We also observe inward migration for smaller mass Pop III protostars/fragments, leading to the rapid merging of sink particles and likely the formation of close binary black holes that, however, reach separations below the resolution of our simulations. We discuss the implications that Pop III separations and ellipticity may have on the interpretation that gravitational wave signals from merging intermediate-mass black holes come from Pop III remnants. [ABSTRACT FROM AUTHOR]

During the Epoch of Reionization (EoR), the ultraviolet radiation from the first stars and galaxies ionized the neutral hydrogen of the intergalactic medium, which can emit radiation through its 21 cm hyperfine transition. Measuring the 21 cm power spectrum is a key science goal for the future Square Kilometre Array (SKA); however, observing and interpreting it is a challenging task. Another high-potential probe of the EoR is the patchy kinetic Sunyaev–Zel'dovich (pkSZ) effect, observed as a foreground to the cosmic microwave background temperature anisotropies on small scales. Despite recent promising measurements, placing constraints on reionization from pkSZ observations is a non-trivial task, subject to strong model dependence. We propose to alleviate the difficulties in observing and interpreting the 21 cm and pkSZ power spectra by combining them. With a simple yet effective parametric model that establishes a formal connection between them, we can jointly fit mock 21 cm and pkSZ data points. We confirm that these observables provide complementary information on reionization, leading to significantly improved constraints when combined. We demonstrate that with as few as two measurements of the 21 cm power spectrum with 100 h of observations with the SKA, as well as a single ℓ = 3000 pkSZ data point, we can reconstruct the reionization history of the universe and its morphology. We find that the reionization history (morphology) is better constrained with two 21 cm measurements at different redshifts (scales). Therefore, a combined analysis of the two probes will give access to tighter constraints on cosmic reionization even in the early stages of 21 cm detections. [ABSTRACT FROM AUTHOR]

We describe JWST /NIRSpec prism measurements of Ly α emission in z ≳ 5 galaxies. We identify Ly α detections in 10 out of 69 galaxies with robust rest-optical emission-line redshift measurements at 5 ≤ z < 7 in the Cosmic Evolution Early Release Science (CEERS) and DDT-2750 observations of the Extended Groth Strip field. Galaxies at z ≃ 6 with faint continuum (F 150 W =27–29 mag) are found with extremely large rest-frame Ly α equivalent widths (EWs; ranging up to 286 Å). Likely Ly α detections are also seen in two new z > 7 galaxies (z  = 7.49 and 7.17) from the second epoch of CEERS observations, both showing large Ly α EWs that likely indicate significant transmission through the intergalactic medium (IGM). We measure high Ly α escape fractions in the 12 Ly α emitters in our sample (median 0.28), two of which show |$f_{\rm esc}^{ {\rm Ly}\alpha }$| near unity (>0.80). We find that |$50_{-11}^{+11}$|  per cent of z ≃ 6 galaxies with [O  iii ] + H β EW>1000 Å have |$f_{\rm esc}^{ {\rm Ly}\alpha }$| >0.2, consistent with the fractions found in lower redshift samples with matched [O  iii ] + H β EWs. While uncertainties are still significant, we find that only |$10_{-5}^{+9}$|  per cent of z > 7 galaxies with similarly strong rest optical emission lines show such large |$f_{\rm esc}^{ {\rm Ly}\alpha }$|⁠ , as may be expected if IGM attenuation of Ly α increases towards higher redshifts. We identify photometric galaxy overdensities near the z ≳ 7 Ly α emitters, potentially providing the ionizing flux necessary to create large ionized sightlines that facilitate Ly α transmission. Finally, we investigate the absence of Ly α emission in a comparable (and spectroscopically confirmed) galaxy overdensity at z  = 7.88 in the Abell 2744 field, discussing new prism spectra of the field obtained with the UNCOVER program. [ABSTRACT FROM AUTHOR]

We examine the evolution of the phase diagram of the low-density intergalactic medium during the Epoch of Reionization in simulation boxes with varying reionization histories from the Cosmic Reionization on Computers project. The probability density function (PDF) of gas temperature at fixed density exhibits two clear modes: a warm and a cold temperature mode, corresponding to the gas inside and outside of ionized bubbles. We find that the transition between the two modes is 'universal' in the sense that its timing is accurately parametrized by the value of the volume-weighted neutral fraction for any reionization history. This 'universality' is more complex than just a reflection of the fact that ionized gas is warm and neutral gas is cold: it holds for the transition at a fixed value of gas density, and gas at different densities transitions from the cold to the warm mode at different values of the neutral fraction, reflecting a non-trivial relationship between the ionization history and the evolving gas density PDF. Furthermore, the 'emergence' of the tight temperature–density relation in the warm mode is also approximately 'universally' controlled by the volume-weighted neutral fraction for any reionization history. In particular, the 'emergence' of the temperature–density relation (as quantified by the rapid decrease in its width) occurs when the neutral fraction is 10−4 ≲ X H  i ≲ 10−3 for any reionization history. Our results indicate that the neutral fraction is a primary quantity controlling the various properties of the temperature–density relation, regardless of reionization history. [ABSTRACT FROM AUTHOR]

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]

The upcoming Square Kilometre Array Observatory will produce images of neutral hydrogen distribution during the epoch of reionization by observing the corresponding 21-cm signal. However, the 21-cm signal will be subject to instrumental limitations such as noise and galactic foreground contamination that pose a challenge for accurate detection. In this study, we present the SegU-Net v2 framework, an enhanced version of our convolutional neural network, built to identify neutral and ionized regions in the 21-cm signal contaminated with foreground emission. We trained our neural network on 21-cm image data processed by a foreground removal method based on Principal Component Analysis achieving an average classification accuracy of 71 per cent between redshift z  = 7 and 11. We tested SegU-Net v2 against various foreground removal methods, including Gaussian Process Regression, Polynomial Fitting, and Foreground-Wedge Removal. Results show comparable performance, highlighting SegU-Net v2 's independence on these pre-processing methods. Statistical analysis shows that a perfect classification score with |${\rm AUC}=95~{{\ \rm per\ cent}}$| is possible for 8 < z < 10. While the network prediction lacks the ability to correctly identify ionized regions at higher redshift and differentiate well the few remaining neutral regions at lower redshift due to low contrast between 21-cm signal, noise, and foreground residual in images. Moreover, as the photon sources driving reionization are expected to be located inside ionized regions, we show that SegU-Net v2 can be used to correctly identify and measure the volume of isolated bubbles with |$V_{\rm ion}\gt (10\, {\rm cMpc})^3$| at z > 9, for follow-up studies with infrared/optical telescopes to detect these sources. [ABSTRACT FROM AUTHOR]

Warm dark matter (WDM) particles with masses (∼ kilo electronvolt) offer an attractive solution to the small-scale issues faced by the cold dark matter (CDM) paradigm. The delay of structure formation in WDM models and the associated dearth of low-mass systems at high redshifts makes this an ideal time to revisit WDM constraints in light of the unprecedented datasets from the JWST. Developing a phenomenological model based on the halo mass functions in CDM and WDM models, we calculate high redshift (⁠|$z \gtrsim 6$|⁠), the stellar mass functions (SMF) and the associated stellar mass density (SMD) and the maximum stellar mass allowed in a given volume. We find that: (i) WDM as light as 1.5 keV is already disfavoured by the low-mass end of the SMF (stellar mass |$M_* \sim 10^7\,\rm M_\odot$|⁠) although caution must be exerted given the impact of lensing uncertainties; (ii) 1.5 keV WDM models predict SMD values that show a steep decrease from 108.8 to |$10^{2}\,\rm M_\odot \rm cMpc^{-3}$| from z ∼ 4 to 17 for |$M_* \gtrsim 10^8\,\rm M_\odot$|⁠ ; and (iii) the 1.5 keV WDM model predicts a sharp and earlier cut-off in the maximum stellar masses for a given number density (or volume) as compared to CDM or heavier WDM models. For example, with a number density of |$10^{-3}\,\rm {cMpc^{-3}}$|⁠ , 1.5 (3) KeV WDM models do not predict bound objects at |$z \gtrsim 12$| (18). Forthcoming JWST observations of multiple blank fields can therefore be used as a strong probe of WDM at an epoch inaccessible by other means. [ABSTRACT FROM AUTHOR]

An ionization front (I-front) that propagates through an inhomogeneous medium is slowed down by self-shielding and recombinations. We perform cosmological radiation hydrodynamics simulations of the I-front propagation during the epoch of cosmic reionization. The simulations resolve gas in mini-haloes (halo mass 104 ≲ Mh [M⊙] ≲ 108) that could dominate recombinations, in a computational volume that is large enough to sample the abundance of such haloes. The numerical resolution is sufficient (gas-particle mass ∼20 M⊙ and spatial resolution <0.1 ckpc) to allow accurate modelling of the hydrodynamic response of gas to photoheating. We quantify the photoevaporation time of mini-haloes as a function of Mh and its dependence on the photoionization rate, Γ−12, and the redshift of reionization, zi. The recombination rate can be enhanced over that of a uniform medium by a factor ∼10−20 early on. The peak value increases with Γ−12 and decreases with zi , due to the enhanced contribution from mini-haloes. The clumping factor, cr , decreases to a factor of a few at ∼100 Myr after the passage of the I-front when the mini-haloes have been photoevaporated; this asymptotic value depends only weakly on Γ−12. Recombinations increase the required number of photons per baryon to reionize the Universe by 20 per cent–100 per cent, with the higher value occurring when Γ−12 is high and zi is low. We complement the numerical simulations with simple analytical models for the evaporation rate and the inverse Strömgren layer. The study also demonstrates the proficiency and potential of sph-m1rt to address astrophysical problems in high-resolution cosmological simulations. [ABSTRACT FROM AUTHOR]

Detection of redshifted H  i 21-cm emission is a potential probe for investigating the Universe's first billion years. However, given the significantly brighter foreground, detecting 21-cm is observationally difficult. The Earth's ionosphere considerably distorts the signal at low frequencies by introducing directional-dependent effects. Here, for the first time, we report the use of Artificial Neural Networks (ANNs) to extract the global 21-cm signal characteristics from the composite all-sky averaged signal, including foreground and ionospheric effects such as refraction, absorption, and thermal emission from the ionosphere's F and D-layers. We assume a 'perfect' instrument and neglect instrumental calibration and beam effects. To model the ionospheric effect, we considered the static and time-varying ionospheric conditions for the mid-latitude region, where LOFAR is situated. In this work, we trained the ANN model for various situations using a synthetic set of the global 21-cm signals created by altering its parameter space based on the ' |$\rm \tanh$| ' parametrized model and the Accelerated Reionization Era Simulations (ARES) algorithm. The obtained result shows that the ANN model can extract the global signal parameters with an accuracy of |${\ge}96\ \hbox{per cent}$| in the final study when we include foreground and ionospheric effects. On the other hand, a similar ANN model can extract the signal parameters from the final prediction data set with an accuracy ranging from 97 to 98 per cent when considering more realistic sets of the global 21-cm signals based on physical models. [ABSTRACT FROM AUTHOR]

The cold dark matter paradigm provides a remarkably good description of the Universe's large-scale structure. However, some discrepancies exist between its predictions and observations at very small sub-galactic scales. To address these issues, the consideration of a strong interaction between dark matter particles and dark radiation emerges as an intriguing alternative. In this study, we explore the constraints on those models using joint observations of cosmic microwave background and quasars absorption spectra with our previously built parameter estimation package cosmoreionmc. At 2σ confidence limits, this analysis rules out the strongly interacting dark matter–dark radiation models within the recently proposed effective theory of structure formation framework, representing the most stringent constraint on those models to the best of our knowledge. Future research using a 21-cm experiment holds the potential to reveal stronger constraints or uncover hidden interactions within the dark sector. [ABSTRACT FROM AUTHOR]

A measurement of the 21-cm global signal would be a revealing probe of the Dark Ages, the era of first star formation, and the Epoch of Reionization. It has remained elusive owing to bright galactic and extra-galactic foreground contaminants, coupled with instrumental noise, ionospheric effects, and beam chromaticity. The simultaneous detection of a consistent 21-cm dipole signal alongside the 21-cm global signal would provide confidence in a claimed detection. We use simulated data to investigate the possibility of using drift-scan dipole antenna experiments to achieve a detection of both monopole and dipole. We find that at least two antennae located at different latitudes are required to localize the dipole. In the absence of foregrounds, a total integration time of ∼104 h is required to detect the dipole. With contamination by simple foregrounds, we find that the integration time required increases to ∼105 h. We show that the extraction of the 21-cm dipole from more realistic foregrounds requires a more sophisticated foreground modelling approach. Finally, we motivate a global network of dipole antennae that could reasonably detect the dipole in ∼103 h of integration time. [ABSTRACT FROM AUTHOR]

With the help of our previously built MCMC (Markov chain Monte Carlo)-based parameter estimation package cosmoreionmc , we investigate in detail the potential of 21 cm global signal, when combined with cosmic microwave background (CMB) and observations related to the Quasar (QSO) absorption spectra, to constraint the mass of warm dark matter (WDM) particle. For the first time, we simultaneously vary all the free parameters (mass of WDM particle, cosmological parameters, and astrophysical parameters) in a joint analysis with CMB, observations related to the QSO absorption spectra and 21 cm global signal, to address the long-overlooked issue of the possible degeneracies between the dark matter particle mass mX and cosmological/astrophysical parameters. From the existing CMB and QSO absorption spectra data, we can rule out mX < 2.8 keV at 95 per cent confidence level. Including a mock 21 cm global signal in the redshift range z  = 25−5 expected to be observed with upcoming instruments designed for global signal, the forecasted constraint is found to be much tighter mX > 7.7 keV, assuming that the true dark matter model is the usual cold dark matter. In case the mock 21 cm signal is constructed for dark matter particles having mX  = 7 keV, our forecasts indicate that (mX /keV)−1 is in the range [0.1, 0.2] (95  per cent confidence level). This implies that the future 21 cm data should allow detection of the WDM particle mass if mX ∼ 7 keV. [ABSTRACT FROM AUTHOR]

The cosmological 21 cm signal is one of the most promising avenues to study the Epoch of Reionization. One class of experiments aiming to detect this signal is global signal experiments measuring the sky-averaged 21 cm brightness temperature as a function of frequency. A crucial step in the interpretation and analysis of such measurements is separating foreground contributions from the remainder of the signal, requiring accurate models for both components. Current models for the signal (non-foreground) component, which may contain cosmological and systematic contributions, are incomplete and unable to capture the full signal. We propose two new methods for extracting this component from the data: First, we employ a foreground-orthogonal Gaussian Process to extract the part of the signal that cannot be explained by the foregrounds. Secondly, we use a FlexKnot parametrization to model the full signal component in a free-form manner, not assuming any particular shape or functional form. This method uses Bayesian model selection to find the simplest signal that can explain the data. We test our methods on both, synthetic data and publicly available EDGES low-band data. We find that the Gaussian Process can clearly capture the foreground-orthogonal signal component of both data sets. The FlexKnot method correctly recovers the full shape of the input signal used in the synthetic data and yields a multimodal distribution of different signal shapes that can explain the EDGES observations. [ABSTRACT FROM AUTHOR]

The physical conditions giving rise to high escape fractions of ionizing radiation (LyC f esc) in star-forming galaxies – most likely protagonists of cosmic reionization – are not yet fully understood. Using the VLT/MUSE observations of ∼1400 Ly α emitters at 2.9 < z < 6.7, we compare stacked rest-frame UV spectra of candidates for LyC leakers and non-leakers selected based on their Ly α profiles. We find that the stacks of potential LyC leakers, i.e. galaxies with narrow, symmetric Ly α profiles with small peak separation, generally show (i) strong nebular O  iii] λ1666, [Si  iii] λ1883, and [C  iii] λ1907 +C  iii] λ1909 emission, indicating a high-ionization state of the interstellar medium (ISM); (ii) high equivalent widths of He  ii λ1640 (∼1 − 3 Å), suggesting the presence of hard ionizing radiation fields; (iii) Si  ii *λ1533 emission, revealing substantial amounts of neutral hydrogen off the line of sight; (iv) high C  iv λλ1548,1550 to [C  iii] λ1907 +C  iii] λ1909 ratios (C iv /C iii ] ≳0.75) , signalling the presence of low column density channels in the ISM. In contrast, the stacks with broad, asymmetric Ly α profiles with large peak separation show weak nebular emission lines, low He  ii λ1640 equivalent widths (≲1 Å), and low C iv /C iii ] (≲0.25), implying low-ionization states and high-neutral hydrogen column densities. Our results suggest that C iv /C iii ] might be sensitive to the physical conditions that govern LyC photon escape, providing a promising tool for identification of ionizing sources among star-forming galaxies in the epoch of reionization. [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 reported detection of the global 21-cm signal by the EDGES collaboration is significantly stronger than standard astrophysical predictions. One possible explanation is an early radio excess above the cosmic microwave background. Such a radio background could have been produced by high-redshift galaxies, if they were especially efficient in producing low-frequency synchrotron radiation. We have previously studied the effects of such an inhomogeneous radio background on the 21-cm signal; however, we made a simplifying assumption of isotropy of the background seen by each hydrogen cloud. Here, we perform a complete calculation that accounts for the fact that the 21-cm absorption occurs along the line of sight, and is therefore sensitive to radio sources lying behind each absorbing cloud. We find that the complete calculation strongly enhances the 21-cm power spectrum during cosmic dawn, by up to two orders of magnitude; on the other hand, the effect on the global 21-cm signal is only at the 5 per cent level. In addition to making the high-redshift 21-cm fluctuations potentially more easily observable, the line-of-sight radio effect induces a new anisotropy in the 21-cm power spectrum. While these effects are particularly large for the case of an extremely enhanced radio efficiency, they make it more feasible to detect even a moderately enhanced radio efficiency in early galaxies. This is especially relevant since the EDGES signal has been contested by the SARAS experiment. [ABSTRACT FROM AUTHOR]