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ABSTRACT: We present the first observational measurements of the Lyman-α (Ly α) forest flux autocorrelation functions in ten redshift bins from 5.1 ≤ z ≤ 6.0. We use a sample of 35 quasar sightlines at z > 5.7 from the extended XQR-30 data set; these data have signal-to-noise ratios of >20 per spectral pixel. We carefully account for systematic errors in continuum reconstruction, instrumentation, and contamination by damped Ly α systems. With these measurements, we introduce software tools to generate autocorrelation function measurements from any simulation. Our measurements of the smallest bin of the autocorrelation function increase with redshift when normalizing by the mean flux, 〈F〉. This increase may come from decreasing 〈F〉 or increasing mean free path of hydrogen-ionizing photons, λmfp. Recent work has shown that the autocorrelation function from simulations at z > 5 is sensitive to λmfp, a quantity that contains vital information on the ending of reionization. For an initial comparison, we show our autocorrelation measurements with simulation models for recently measured λmfp values and find good agreements. Further work in modelling and understanding the covariance matrices of the data is necessary to get robust measurements of λmfp from this data.

We present a neural network emulator to constrain the thermal parameters of the intergalactic medium (IGM) at |$5.4 \le z \le 6.0$| using the Lyman- |$\alpha$| (Ly  |$\alpha$|⁠) forest flux autocorrelation function. Our autodifferentiable JAX -based framework accelerates the surrogate model generation process using approximately 100 sparsely sampled Nyx hydrodynamical simulations with varying combinations of thermal parameters, i.e. the temperature at mean density |$T_0$|⁠ , the slope of the temperature–density relation |$\gamma$|⁠ , and the mean transmission flux |$\langle F \rangle$|⁠. We show that this emulator has a typical accuracy of 1.0 per cent across the specified redshift range. Bayesian inference of the IGM thermal parameters, incorporating emulator uncertainty propagation, is further expedited using NumPyro Hamiltonian Monte Carlo. We compare both the inference results and computational cost of our framework with the traditional nearest-neighbour interpolation approach applied to the same set of mock Ly  |$\alpha$| flux. By examining the credibility contours of the marginalized posteriors for |$T_0, \gamma , \text{and}~\langle F \rangle$| obtained using the emulator, the statistical reliability of measurements is established through inference on 100 realistic mock data sets of the autocorrelation function. [ABSTRACT FROM AUTHOR]

Ly |$\alpha$| is the transition to the ground state from the first excited state of hydrogen (the most common element). Resonant scattering of this line by neutral hydrogen greatly impedes its emergence from galaxies, so the fraction of galaxies emitting Ly |$\alpha$| is a tracer of the neutral fraction of the intergalactic medium (IGM), and thus the history of reionization. In previous works, we used early JWST /NIRSpec data from the JWST Advanced Deep Extragalactic Survey (JADES) to classify and characterize Ly |$\alpha$| emitting galaxies (LAEs). This survey is approaching completion, and the current sample is nearly an order of magnitude larger. From a sample of 795  galaxies in JADES at |$4.0\lt z\lt 14.3$|⁠ , we find evidence for Ly |$\alpha$| emission in 150 sources. We reproduce the previously found correlation between Ly |$\alpha$| escape fraction (⁠|$f\rm _{esc}^{Ly\alpha }$|⁠) – Ly |$\alpha$| rest-frame equivalent width (⁠|${\rm REW}_{\rm Ly\alpha }$|⁠) and the negative correlation between Ly |$\alpha$| velocity offset – |$f\rm _{esc}^{Ly\alpha }$|⁠. Both |$f\rm _{esc}^{Ly\alpha }$| and |${\rm REW}_{\rm Ly\alpha }$| decrease with redshift (⁠|$z\gtrsim 5.5$|⁠), indicating the progression of reionization on a population scale. Our data are used to demonstrate an increasing IGM transmission of Ly |$\alpha$| from |$z\sim 14-6$|⁠. We measure the completeness-corrected fraction of LAEs (⁠|$X\rm _{Ly\alpha }$|⁠) from |$z=4-9.5$|⁠. An application of these |$X\rm _{Ly\alpha }$| values to the results of previously utilized semi-analytical models suggests a high neutral fraction at |$z=7$| (⁠|${X_{\rm HI}}\sim 0.8-0.9$|⁠). Using an updated fit to the intrinsic distribution of |${\rm REW}_{\rm Ly\alpha }$| results in a lower value in agreement with current works (⁠|${X_{\rm HI}}= 0.64_{-0.21}^{+0.13}$|⁠). This sample of LAEs will be paramount for unbiased population studies of galaxies in the EoR. [ABSTRACT FROM AUTHOR]

The tumultuous effects of ultraviolet photons that source cosmic reionization, the subsequent compression and shock-heating of low-density regions, and the modulation of baryons in shallow potential wells induced by the passage of ionization fronts, collectively introduce perturbations to the evolution of the intergalactic medium in the post-reionization era. These enduring fluctuations persist deep into the post-reionization era, casting a challenge upon precision cosmology endeavours targeting tracers in this cosmic era. Simultaneously, these relics from reionization also present a unique opportunity to glean insights into the astrophysics that govern the epoch of reionization. In this work, we propose a first study of the cross-correlation of Ly |$\alpha$| forest and 21 cm intensity mapping, accounting for the repercussions of inhomogeneous reionization in the post-reionization era. We investigate the ability of Square Kilometre Array (SKA) |$\times$| Dark Energy Spectroscopic Instrument (DESI)-like, SKA |$\times$| MUltiplexed Survey Telescope (MUST)-like, and Packed Ultra-wideband Mapping Array (PUMA) |$\times$| MUST-like instrumental set-ups to achieve a high-signal-to-noise ratio (SNR) in the redshift range |$3.5 \le z \le 4$|⁠. Moreover, we assess how alterations in integration time, survey area, and reionization scenarios impact the SNR. Furthermore, we forecast the cross-correlation's potential to constrain cosmological parameters under varying assumptions: considering or disregarding reionization relics, marginalizing over reionization astrophysics, and assuming perfect knowledge of reionization. Notably, our findings underscore the remarkable capability of a futuristic PUMA |$\times$| MUST-like set-up, with a modest 100-h integration time over a 100 deg2 survey, to constrain the ionization efficiency error to |$\sigma _\zeta = 3.42$|⁠. [ABSTRACT FROM AUTHOR]

Given the sensitivity of the resonant Lyman |$\alpha$| (Ly  |$\alpha $|⁠) transition to absorption by neutral hydrogen, observations of Ly  |$\alpha$| emitting galaxies (LAEs) have been widely used to probe the ionizing capabilities of reionization-era galaxies and their impact on the intergalactic medium (IGM). However, prior to JWST our understanding of the contribution of fainter sources and of ionized 'bubbles' at earlier stages of reionization remained uncertain. Here, we present the characterization of three exceptionally distant LAEs at |$z \gt 8$|⁠ , newly discovered by JWST /Near-Infrared Spectrograph in the JADES survey. These three similarly bright (⁠|$M_\text{UV} \approx -20 \, \mathrm{mag}$|⁠) LAEs exhibit small Ly  |$\alpha$| velocity offsets from the systemic redshift, |$\Delta v_\rm{{Ly\alpha }} \lesssim 200 \, \mathrm{km \, s^{-1}}$|⁠ , yet span a range of Ly  |$\alpha$| equivalent widths (15, 31, and |$132 \, \mathring{\rm A}$|⁠). The former two show moderate Ly  |$\alpha$| escape fractions (⁠|$f_\rm{esc, {Ly\alpha }} \approx 10~{{\rm per\,cent}}$|⁠), whereas Ly  |$\alpha$| escapes remarkably efficiently from the third (⁠|$f_\rm{esc, {Ly\alpha }} \approx 72~{{\rm per\,cent}}$|⁠), which moreover is very compact (half-light radius of |$90 \pm 10 \, \mathrm{pc}$|⁠). We find these LAEs are low-mass galaxies dominated by very recent, vigorous bursts of star formation accompanied by strong nebular emission from metal-poor gas. We infer the two LAEs with modest |$f_\rm{esc, {Ly\alpha }}$|⁠ , one of which reveals evidence for ionization by an active galactic nucleus, may have reasonably produced small ionized bubbles preventing complete IGM absorption of Ly  |$\alpha$|⁠. The third, however, requires a |$\sim \!3 \, \text{physical Mpc}$| bubble, indicating faint galaxies have contributed significantly. The most distant LAEs thus continue to be powerful observational probes into the earlier stages of reionization. [ABSTRACT FROM AUTHOR]

Radio interferometers targeting the 21cm brightness temperature fluctuations at high redshift are subject to systematic effects that operate over a range of different time-scales. These can be isolated by designing appropriate Fourier filters that operate in fringe-rate (FR) space, the Fourier pair of local sidereal time. Applications of FR filtering include separating effects that are correlated with the rotating sky versus those relative to the ground, down-weighting emission in the primary beam sidelobes, and suppressing noise. FR filtering causes the noise contributions to the visibility data to become correlated in time, however, making interpretation of subsequent averaging and error estimation steps more subtle. In this paper, we describe fringe-rate filters that are implemented using discrete prolate spheroidal sequences, and designed for two different purposes–beam sidelobe/horizon suppression (the 'mainlobe' filter), and ground-locked systematics removal (the 'notch' filter). We apply these to simulated data, and study how their properties affect visibilities and power spectra generated from the simulations. Included is an introduction to fringe-rate filtering and a demonstration of fringe-rate filters applied to simple situations to aid understanding. [ABSTRACT FROM AUTHOR]

We use NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) to study the ionizing properties of a sample of 14 652 galaxies at |$3 \le z_{\rm {phot}} \le 9$|⁠ , 90 per cent complete in stellar mass down to log(M |$_{\star }$| /[M |$_{\odot }])\approx 7.5$|⁠. Out of the full sample, 1620 of the galaxies have spectroscopic redshift measurements from the literature. We use the spectral energy distribution fitting code Prospector to fit all available photometry and infer galaxy properties. We find a significantly milder evolution of the ionizing photon production efficiency (⁠|$\xi _{\rm {ion}}$|⁠) with redshift and UV magnitude than previously reported. Interestingly, we observe two distinct populations in |$\xi _{\rm {ion}}$|⁠ , distinguished by their burstiness (given by SFR |$_{10}$| /SFR |$_{100}$|⁠). Both populations show the same evolution with z and M |$_{\rm {UV}}$|⁠ , but have a different |$\xi _{\rm {ion}}$| normalization. We convolve the more representative |$\log (\xi _{\rm {ion}} (z,\text{M}_{\rm {UV}}))$| relations (accounting for |$\sim 97$| % of the sample), with luminosity functions from literature, to place constraints on the cosmic ionizing photon budget. By combining our results, we find that one of our models can match the observational constraints from the Ly  |$\alpha$| forest at |$z\lesssim 6$|⁠. We conclude that galaxies with M |$_{\rm {UV}}$| between |$-16$| and |$-20$|⁠ , adopting a reasonable escape fraction, can produce enough ionizing photons to ionize the Universe, without exceeding the required ionizing photon budget. [ABSTRACT FROM AUTHOR]

We study the viability of using power spectrum clustering wedges as summary statistics of 21 cm surveys during the epoch of reionization (EoR). For observations in a wide redshift range |$z\sim 7{\!-\!}9$| corresponding to a line-of-sight scale of |$\sim 500\,$|  Mpc, the power spectrum is subject to anisotropic effects due to the evolution along the light of sight. Information on the physics of reionization can be extracted from the anisotropy using the power spectrum multipoles. Signals of the power spectrum monopole are highly correlated at scales smaller than the typical ionization bubble, which can be disentangled by including higher-order multipoles. By simulating observations of the low-frequency part of the Square Kilometre Array (SKA) Observatory, we find that the sampling of the cylindrical wavenumber |$\boldsymbol {k}$| -space is highly non-uniform due to the baseline distribution, i.e. the distribution of antenna pairs sampling different transverse |$\boldsymbol {k}_\perp$| scales. Measurements in clustering wedges partition the cylindrical |$\boldsymbol {k}$| -space into different radial |$k_\parallel$| scales, and can be used for isolating parts of |$\boldsymbol {k}$| -space with relatively uniform sampling, allowing for more precise parameter inference. Using Fisher Matrix forecasts, we find that the reionization model can be inferred with per cent level precision with |$\sim 120$|  h of integration time using SKA-Low. Compared to model inference using only the power spectrum monopole above the foreground wedge, model inference using multipole power spectra in clustering wedges yields a factor of |$\sim 3$| improvement on the marginalized 1D parameter constraints. [ABSTRACT FROM AUTHOR]

Lyman- |$\alpha$| photons enable the cosmic dawn 21-cm signal through a process called the Wouthuysen–Field effect. An accurate model of the signal in this epoch hinges on the accuracy of the computation of the Ly |$\alpha$| coupling, which requires one to calculate the specific intensity of Ly |$\alpha$| photons emitted from the first stars. Most traditional calculations of the Ly |$\alpha$| coupling assume a delta-function scattering cross-section, as the resonant nature of the Ly |$\alpha$| scattering makes an accurate radiative transfer (RT) solution computationally expensive. Attempts to improve upon this traditional approach using numerical RT have recently emerged. However, some of these treatments suffer from assumptions such as a uniform gas distribution, coherent scattering in the gas frame, and isotropic scattering. While others which do not account for these only do so through certain schemes along with core-skipping algorithms. We present results from a self-consistent Monte Carlo RT simulations devoid of any of the assumptions in the previous work for the first time. We find that gas bulk motion is the most important effect to account for in RT resulting in an RMS difference of 38 per cent in the 21-cm signal and anisotropic scattering being the least important effect contributing to less than 3 per cent RMS difference in 21-cm signal. We also evaluate the 21-cm power spectrum and compare that with the traditional results at cosmic dawn. This work points the way towards higher-accuracy models to enable better inferences from future measurements. [ABSTRACT FROM AUTHOR]

We present the census of H  |$\beta$|  + [ |${\rm O\, {\small III}}$| ] |$4960,5008\rm{\mathring{\rm\,A}}$| emitters at |$6.8\lt z\lt 9.0$| from the JWST FRESCO survey over 124 arcmin |$^2$| in the GOODS-North and GOODS-South fields. Our unbiased spectroscopic search results in 137 spectroscopically confirmed galaxies at |$6.8\lt z\lt 9.0$| with observed [ |${\rm O\, {\small III}}$| ] fluxes |$f_{\rm { [{\rm O\, {\small III}}]}}\gtrsim 1\times 10^{-18}\ \rm {ergs}\ \rm {s}^{-1} \ \rm {cm}^{-2}$|⁠. The rest-frame optical line ratios of the median stacked spectrum (median |$M_{\rm {UV}}=-19.65^{+0.59}_{-1.05}$|⁠) indicate negligible dust attenuation, low metallicity (⁠|$12+\log (\rm {O/H})= 7.2-7.7$|⁠) and a high ionization parameter |$\log _{10}U \simeq -2.5$|⁠. We find a factor |$\times 1.3$| difference in the number density of |$6.8\lt z\lt 9.0$| galaxies between GOODS-South and GOODS-North, which is caused by a single overdensity at |$7.0\lt z\lt 7.2$| in GOODS-North. The bright end of the UV luminosity function of spectroscopically confirmed [ |${\rm O\, {\small III}}$| ] emitters is in good agreement with HST dropout-selected samples. Discrepancies between the observed [ |${\rm O\, {\small III}}$| ] LF, [ |${\rm O\, {\small III}}$| ]/UV ratio, and [ |${\rm O\, {\small III}}$| ] equivalent widths, and that predicted by theoretical models, suggest burstier star-formation histories and/or more heterogeneous metallicity and ionizing conditions in |$z\gt 7$| galaxies. We report a rapid decline of the [ |${\rm O\, {\small III}}$| ] luminosity density at |$z\gtrsim 6\!-\!7$| which cannot be explained by the evolution of the cosmic star-formation rate density. Finally we find that FRESCO detects in only 2h galaxies likely accounting for |$\sim 10-20{{\ \rm per\ cent}}$| of the ionizing budget at |$z=7\!-\!8$| (assuming an escape fraction of |$10{{\ \rm per\ cent}}$|⁠), raising the prospect of directly detecting a significant fraction of the sources of reionization with JWST. [ABSTRACT FROM AUTHOR]

Power spectrum estimators are an important tool in efforts to detect the 21 cm brightness temperature fluctuations from neutral hydrogen at early times. An initial detection will likely be statistical in nature, meaning that it will not be possible to make a coherent map of the brightness temperature fluctuations; instead, only their variance will be measured against a background of noise and residual systematic effects. Optimal quadratic estimator-based methods often apply an inverse covariance weighting to the data. However, inaccurate covariance modelling can lead to reduced sensitivity and, in some cases, severe signal loss. We recently proposed a Bayesian method to jointly estimate the 21 cm fluctuations, their power spectrum, and foreground emission. Instead of requiring a fixed a priori estimate of the covariance, we estimate the covariance as part of the inference. Choices of parametrization, particularly of the foregrounds, are subject to model errors and could lead to biases and other ill effects if not properly controlled. In this paper, we investigate the effects of inaccurate foreground models on 21 cm power spectrum recovery. Using simulated visibilities, we find that, even in the most extreme scenarios tested, our approach is capable of recovering 21 cm delay power spectrum estimates consistent with a known input signal for delays |$\gtrsim 300$| ns (⁠|$\sim$| 88 per cent of the available Fourier modes). This is true even when using foreground models derived from modified foreground catalogues containing spatial and spectral perturbations at the quoted level of uncertainty on our foreground catalogues. [ABSTRACT FROM AUTHOR]

The 21 cm transition from neutral Hydrogen promises to be the best observational probe of the Epoch of Reionization (EoR). This has led to the construction of low-frequency radio interferometric arrays, such as the Hydrogen Epoch of Reionization Array (HERA), aimed at systematically mapping this emission for the first time. Precision calibration, however, is a requirement in 21 cm radio observations. Due to the spatial compactness of HERA, the array is prone to the effects of mutual coupling, which inevitably lead to non-smooth calibration errors that contaminate the data. When unsmooth gains are used in calibration, intrinsically spectrally smooth foreground emission begins to contaminate the data in a way that can prohibit a clean detection of the cosmological EoR signal. In this paper, we show that the effects of mutual coupling on calibration quality can be reduced by applying custom time-domain filters to the data prior to calibration. We find that more robust calibration solutions are derived when filtering in this way, which reduces the observed foreground power leakage. Specifically, we find a reduction of foreground power leakage by 2 orders of magnitude at |$k_\parallel \approx 0.5$| h Mpc |$^{-1}$|⁠. [ABSTRACT FROM AUTHOR]

New JWST observations are revealing the first galaxies to be prolific producers of ionizing photons, which we argue gives rise to a tension between different probes of reionization. Over the last two decades, a consensus has emerged where star-forming galaxies are able to generate enough photons to drive reionization, given reasonable values for their number densities, ionizing efficiencies |$\xi _{\rm ion}$| (per unit ultraviolet luminosity), and escape fractions |$f_{\rm esc}$|⁠. However, some new JWST observations infer high values of |$\xi _{\rm ion}$| during reionization and an enhanced abundance of earlier (⁠|$z\gtrsim 9$|⁠) galaxies, dramatically increasing the number of ionizing photons produced at high z. Simultaneously, recent low- z studies predict significant escape fractions for faint reionization-era galaxies. Put together, we show that the galaxies we have directly observed (⁠|$M_{\rm UV} < -15$|⁠) not only can drive reionization, but would end it too early. That is, our current galaxy observations, taken at face value, imply an excess of ionizing photons and thus a process of reionization in tension with the cosmic microwave background and Lyman- |$\alpha$| forest. Considering galaxies down to |$M_{\rm UV}\approx -11$|⁠ , below current observational limits, only worsens this tension. We discuss possible avenues to resolve this photon budget crisis, including systematics in either theory or observations. [ABSTRACT FROM AUTHOR]

A first statistical detection of the 21-cm Epoch of Reionization (EoR) is on the horizon, as cosmological volumes of the Universe become accessible via the adoption of low-frequency interferometers. We explore the impact which non-identical instrumental beam responses can have on the calibrated power spectrum and a future EoR detection. All-sky satellite measurements of Murchison Widefield Array (MWA) beams have revealed significant sidelobe deviations from cutting-edge electromagnetic simulations at the |${\sim} 10~{{\ \rm per\ cent}}$| zenith power level. By generating physically motivated deformed beam models, we emulate real measurements of the MWA which inherently encode the imprints of varied beams. We explore two calibration strategies: using a single beam model across the array, or using a full set of deformed beams. Our simulations demonstrate beam-induced leakage of foreground power into theoretically uncontaminated modes, at levels which exceed the expected cosmological signal by factors of over |$\sim$| 1000 between the modes k  = 0.1–1 |$h\mathrm{Mpc}^{-1}$|⁠. We also show that this foreground leakage can be mitigated by including measured models of varied beams into calibration frameworks, reducing the foreground leakage to a sub-dominant effect and potentially unveiling the EoR. Finally, we outline the future steps necessary to make this approach applicable to real measurements by radio interferometers. [ABSTRACT FROM AUTHOR]

Observations with radio arrays that target the 21-cm signal originating from the early Universe suffer from a variety of systematic effects. An important class of these is reflections and spurious couplings between antennas. We apply a Hamiltonian Monte Carlo sampler to the modelling and mitigation of these systematics in simulated Hydrogen Epoch of Reionization Array (HERA) data. This method allows us to form statistical uncertainty estimates for both our models and the recovered visibilities, which is an important ingredient in establishing robust upper limits on the epoch of reionization (EoR) power spectrum. In cases where the noise is large compared to the EoR signal, this approach can constrain the systematics well enough to mitigate them down to the noise level for both systematics studied. Incoherently averaging the recovered power spectra can further reduce the noise and improve recovery. Where the noise level is lower than the EoR, our modelling can mitigate the majority of the reflections and coupling with there being only a minor level of residual systematics. Our approach performs similarly to existing filtering/fitting techniques used in the HERA pipeline, but with the added benefit of rigorously propagating uncertainties. In all cases it does not significantly attenuate the underlying signal. [ABSTRACT FROM AUTHOR]

Twenty-one-centimetre signals from the Epoch of Reionization (EoR) are expected to be detected in the low-frequency radio window by the next-generation interferometers, particularly the Square Kilometre Array (SKA). However, precision data analysis pipelines are required to minimize the systematics within an infinitesimal error budget. Consequently, there is a growing need to characterize the sources of errors in EoR analysis. In this study, we identify one such error origin, namely source blending, which is introduced by the overlap of objects in the densely populated observing sky under SKA1-Low's unprecedented sensitivity and resolution, and evaluate its two-fold impact in both the spatial and frequency domains using a novel hybrid evaluation (HEVAL) pipeline combining end-to-end simulation with an analytic method to mimic EoR analysis pipelines. Sky models corrupted by source blending induce small but severe frequency-dependent calibration errors when coupled with astronomical foregrounds, impeding EoR parameter inference with strong additive residuals in the two-dimensional power spectrum space. We report that additive residuals from poor calibration against sky models with blending ratios of 5 and 0.5 per cent significantly contaminate the EoR window. In contrast, the sky model with a 0.05 per cent blending ratio leaves little residual imprint within the EoR window, therefore identifying a blending tolerance at approximately 0.05 per cent. Given that the SKA observing sky is estimated to suffer from an extended level of blending, strategies involving de-blending, frequency-dependent error mitigation, or a combination of both, are required to effectively attenuate the calibration impact of source-blending defects. [ABSTRACT FROM AUTHOR]

The gravitational wave (GW) signal from binary black hole (BBH) mergers is a promising probe of Population III (Pop III) stars. To fully unleash the power of the GW probe, one important step is to understand the relative importance and features of different BBH evolution channels. We model two channels, isolated binary stellar evolution (IBSE) and nuclear star cluster-dynamical hardening (NSC-DH), in one theoretical framework based on the semi-analytical code a-sloth , under various assumptions on Pop III initial mass function (IMF), initial binary statistics and high- z nuclear star clusters (NSCs). The NSC-DH channel contributes |$\sim 8\!-\!95{{\ \rm per\ cent}}$| of Pop III BBH mergers across cosmic history, with higher contributions achieved by initially wider binary stars, more top-heavy IMFs, and more abundant high- z NSCs. The dimensionless stochastic GW background (SGWB) produced by Pop III BBH mergers has peak values |$\Omega ^{\rm peak}_{\rm GW}\sim 10^{-11}\!-\!8\times 10^{-11}$| around observer-frame frequencies |$\nu \sim 10\!-\!100\ \rm Hz$|⁠. The Pop III contribution can be a non-negligible (⁠|$\sim 2\!-\!32{{\ \rm per\ cent}}$|⁠) component in the total SGWB at |$\nu \lesssim 10\ \rm Hz$|⁠. The estimated detection rates of Pop III BBH mergers by the Einstein Telescope are |$\sim 6\!-\!230$| and |$\sim 30\!-\!1230\ \rm yr^{-1}$| for the NSC-DH and IBSE channels, respectively. Pop III BBH mergers in NSCs are more massive than those from IBSE, so they dominate the Pop III SGWB below 20 Hz in most cases. Besides, the detection rate of Pop III BBH mergers involving at least one intermediate-mass BH above |$100\ \rm M_\odot$| by the Einstein Telescope is |$\sim 0.5\!-\!200\ \rm yr^{-1}$| in NSCs but remains below |$0.1\ \rm yr^{-1}$| for IBSE. [ABSTRACT FROM AUTHOR]

The contribution of resolved and unresolved extragalactic point sources to the low-frequency sky spectrum is a potentially non-negligible part of the astrophysical foregrounds for cosmic dawn 21-cm experiments. The clustering of such point sources on the sky, combined with the frequency dependence of the antenna beam, can also make this contribution chromatic. By combining low-frequency measurements of the luminosity function and the angular correlation function of extragalactic point sources, we develop a model for the contribution of these sources to the low-frequency sky spectrum. Using this model, we find that the contribution of sources with flux density |${\gt} 10^{-6}$|  Jy to the sky-averaged spectrum is smooth and of the order of a few kelvins at 50–200 MHz. We combine this model with measurements of the galactic foreground spectrum and weigh the resultant sky by the beam directivity of the conical log-spiral antenna planned as part of the Radio Experiment for the Analysis of Cosmic Hydrogen (REACH) project. We find that the contribution of point sources to the resultant spectrum is |${\sim}\, 0.4 {{\, \rm per\, cent}}$| of the total foregrounds, but still larger by at least an order of magnitude than the standard predictions for the cosmological 21-cm signal. As a result, not accounting for the point-source contribution leads to a systematic bias in 21-cm signal recovery. We show, however, that in the REACH case, this reconstruction bias can be removed by modelling the point-source contribution as a power law with a running spectral index. We make our code publicly available as a python package labelled epspy. [ABSTRACT FROM AUTHOR]

JWST has brought us new insights into Cosmic Dawn with tentative detection of the unique signatures of metal-free Population III (Pop III) stars, such as strong He II emission, extremely blue ultraviolet spectrum, and enhanced nitrogen abundance. Self-consistent theoretical predictions of the formation rates, sites, and masses of Pop III stars are crucial for interpreting the observations, but are challenging due to complex physical processes operating over the large range of length-scales involved. One solution is to combine analytical models for the small-scale star formation process with cosmological simulations that capture the large-scale physics such as structure formation, radiation backgrounds, and baryon-dark matter streaming motion that regulate the conditions of Pop III star formation. We build an analytical model to predict the final masses of Pop III stars/clusters from the properties of star-forming clouds, based on the key results of small-scale star formation simulations and stellar evolution models. Our model for the first time considers the interplay between feedback and fragmentation and covers different modes of Pop III star formation ranging from ordinary small (⁠|$\sim\!{10{-}2000}\ \rm M_\odot$|⁠) clusters in molecular-cooling clouds to massive (⁠|$\gtrsim\!{10^{4}}\ \rm M_\odot$|⁠) clusters containing supermassive (⁠|$\sim\!{10^{4}{-}3}\times 10^{5}\ \rm M_\odot$|⁠) stars under violent collapse of atomic-cooling clouds with large gas accretion rates of |$\gtrsim\!{0.1}\ \rm M_\odot \ yr^{-1}$|⁠. As an example, the model is applied to the Pop III star-forming clouds in the progenitors of typical haloes hosting high- z luminous quasars (⁠|$M_{\rm h}\sim 10^{12}\ \rm M_\odot$| at |$z\sim 6$|⁠), which shows that formation of Pop III massive clusters is common (⁠|$\sim\!{20{-}70}{{\ \rm per\ cent}}$|⁠) in such biased (⁠|$\sim\!{4}\sigma$|⁠) regions, and the resulting heavy black hole seeds from supermassive stars can account for a significant fraction of observed luminous (⁠|$\gtrsim\!{10^{46}}\ \rm erg\ s^{-1}$|⁠) quasars at |$z\sim 6$|⁠. [ABSTRACT FROM AUTHOR]

The use of Gaussian Process Regression (GPR) for foregrounds mitigation in data collected by the LOw-Frequency ARray (LOFAR) to measure the high-redshift 21-cm signal power spectrum has been shown to have issues of signal loss when the 21-cm signal covariance is misestimated. To address this problem, we have recently introduced covariance kernels obtained by using a Machine Learning based Variational Auto-Encoder (VAE) algorithm in combination with simulations of the 21-cm signal. In this work, we apply this framework to 141 h (⁠|${\approx} 10$| nights) of LOFAR data at |$z \approx 9.1$|⁠ , and report revised upper limits of the 21-cm signal power spectrum. Overall, we agree with past results reporting a 2- |$\sigma$| upper limit of |$\Delta ^2_{21} \ \lt\ (80)^2~\rm mK^2$| at |$k = 0.075~h~\rm Mpc^{-1}$|⁠. Further, the VAE-based kernel has a smaller correlation with the systematic excess noise, and the overall GPR-based approach is shown to be a good model for the data. Assuming an accurate bias correction for the excess noise, we report a 2- |$\sigma$| upper limit of |$\Delta ^2_{21} \ \lt\ (25)^2~\rm mK^2$| at |$k = 0.075~h~\rm Mpc^{-1}$|⁠. However, we still caution to take the more conservative approach to jointly report the upper limits of the excess noise and the 21-cm signal components. [ABSTRACT FROM AUTHOR]

The Cosmic Dawn was marked by the formation of the first stars, and preceded the Epoch of Reionization (EoR), when the Universe underwent a fundamental transformation caused by the radiation from these first stars and galaxies. Interferometric 21-cm experiments aim to probe redshifted neutral hydrogen signals from these periods, constraining the conditions of the early Universe. The SKA-Low instrument of the Square Kilometre Array (SKA) is envisaged to be the largest and most sensitive radio telescope at metre and centimetre wavelengths. The latest Aperture Array Verification Systems feature 7-m coaxial transmission lines connecting the low noise amplifiers to optical transmitters at the front of the analogue-receiving chain. An impedance mismatch between these components results in a partially reflected electromagnetic signal, introducing chromatic aberrations into the instrument bandpass. This causes power from the foreground signals to appear at higher delays, potentially contaminating the 'EoR window', a region in which the 21-cm signal should be detectable. We present an end-to-end simulation pipeline for SKA-Low using a composite sky model combining radio foregrounds from the Galactic and Extragalactic All-Sky MWA (GLEAM) Survey, Haslam 408 MHz, and a 1.5-cGpc 21-cm brightness temperature cube generated with the 21cm space simulator. We derive a model for the scattering parameters of a coaxial transmission line in terms of its specifications and bulk material properties. Assuming identical cables of length |$\le 15.0$|  m with impedance mismatch |$\le 10\, \Omega$|⁠ , the reflection is confined below the EoR window. However, we demonstrate that even a 0.1 per cent length tolerance introduces contamination with an absolute fractional difference of ~10 per cent across all accessible k-modes. [ABSTRACT FROM AUTHOR]

We present a new suite of late-end reionization simulations performed with aton-he , a revised version of the GPU-based radiative transfer code aton that includes helium. The simulations are able to reproduce the Ly  |$\alpha$| flux distribution of the E-XQR-30 sample of QSO absorption spectra at |$5 \lesssim z \lesssim 6.2$|⁠ , and show that a large variety of reionization models are consistent with these data. We explore a range of variations in source models and in the early-stage evolution of reionization. Our fiducial reionization history has a mid-point of reionization at |$z = 6.5$|⁠ , but we also explore an 'Early' reionization history with a mid-point at |$z = 7.5$| and an 'Extremely Early' reionization history with a mid-point at |$z = 9.5$|⁠. Haloes massive enough to host observed Ly  |$\alpha$| emitters are highly biased. The fraction of such haloes embedded in ionized bubbles that are large enough to allow high Ly  |$\alpha$| transmission becomes close to unity much before the volume filling factor of ionized regions. For our fiducial reionization history this happens at |$z = 8$|⁠ , probably too late to be consistent with the detection by JWST of abundant Ly  |$\alpha$| emission out to |$z = 11$|⁠. A reionization history in our 'Early' model or perhaps even our 'Extremely Early' model may be required, suggesting a Thomson scattering optical depth in tension with that reported by Planck, but consistent with recent suggestions of a significantly higher value. [ABSTRACT FROM AUTHOR]

Gravitational lensing may render individual high-mass stars detectable out to cosmological distances, and several extremely magnified stars have in recent years been detected out to redshifts |$z\approx 6$|⁠. Here, we present Muspelheim, a model for the evolving spectral energy distributions of both metal-enriched and metal-free stars at high redshifts. Using this model, we argue that lensed stars will form a highly biased sample of the intrinsic distribution of stars across the Hertzsprung–Russell diagram, and that this bias will typically tend to favour the detection of lensed stars in evolved stages characterized by low effective temperatures, even though stars only spend a minor fraction of their lifetimes in such states. We also explore the prospects of detecting individual, lensed metal-free (Population III) stars at high redshifts using the James Webb Space Telescope (JWST). We find that very massive (⁠|$\gtrsim 100\ \mathrm{M}_\odot$|⁠) Population III stars at |$z\gtrsim 6$| may potentially be detected by JWST in surveys covering large numbers of strong-lensing clusters, provided that the Population III stellar initial mass function is sufficiently top-heavy, that these stars evolve to effective temperatures |$\le 15000$| K, and that the cosmic star formation rate density of Pop III stars reaches |$\gtrsim 10^{-4}\ \mathrm{M}_\odot$| cMpc |$^{-3}$| yr |$^{-1}$| at |$z\approx 6$| –10. Various ways to distinguish metal-free lensed stars from metal-enriched ones are also discussed. [ABSTRACT FROM AUTHOR]

The escaping ionising efficiency from galaxies, fescξion, is a crucial ingredient for understanding their contribution to hydrogen reionisation, but both of its components, fesc and ξion, are extremely difficult to measure. We measured the average escaping ionising efficiency ⟨fescξion⟩ of galaxies at z = 5 implied by the mean level of ionisation in the intergalactic medium via the Lyman-α forest. We used the fact that Nion = ρUVfescξion, N ˙ ion = ρ UV f esc ξ ion the product of the ionising output and the UV density ρUV, can be calculated from the known average strength of the UV background and the mean free path of ionising photons. These quantities, as well as ρUV, are robustly measured at z ≤ 6. We calculated the missing factor of ⟨fescξion⟩ at z = 5 during a convenient epoch after hydrogen reionisation had been completed and the intergalactic medium had reached ionisation equilibrium but before bright quasars began to dominate the ionising photon production. Intuitively, our constraint corresponds to the required escaping ionising production from galaxies in order to avoid over- or under-ionising the Lyman-α forest. We obtained a measurement of log⟨fescξion⟩/erg Hz-1 = 24.28+0.21-0.20 − 1 = 24. 28 − 0.20 + 0.21 at z = 5 when integrating the ρUV down to a limiting magnitude Mlim = −11. Our measurement of the escaping ionising efficiency of galaxies is in rough agreement with both observations of early galaxies and with most models. [ABSTRACT FROM AUTHOR]

Deep imaging of galaxy cluster fields have in recent years revealed tens of candidates for gravitationally lensed stars at redshifts z ≈ 1 − 6, and future searches are expected to reveal highly magnified stars from even earlier epochs. Multi-band photometric observations may be used to constrain the redshift, effective temperature Teff, and dust attenuation along the line of sight to such objects. When combined with an estimate of the likely magnification, these quantities may be converted into a constraint on the stellar luminosity and, for an adopted set of stellar evolutionary tracks, the initial stellar mass. Further characterisation is difficult, however, without spectroscopic observations, which at the typical brightness levels of high-redshift lensed stars becomes extremely challenging for even the largest existing telescopes. Here, we explore what spectral features one can realistically hope to detect in lensed stars with peak brightness in the range 26–28 AB mag, Teff = 4000 − 50 000 K, and redshifts z = 1 − 10, using spectroscopy with JWST and the forthcoming ELT. We find that a majority of detectable lines appear in the rest-UV range for stars with Teff ≥ 15 000 K. The strongest detectable spectral lines are the C IVλ1550 Å line and the Si IVλλ1393, 1403 Å-doublet at Teff = 30 000 K. For lower temperatures, the calcium H- and K-lines at Teff = 6000 K are among the most readily detectable. In limited wavelength ranges, ELT is expected to provide more sensitive spectroscopic observations, and with higher resolution than JWST. We find that variations in both mass-loss rate and metallicity lead to noticeable effects in the detectability of certain spectral lines with both JWST and ELT. [ABSTRACT FROM AUTHOR]

During the epoch of reionization (EoR), the 21-cm signal allows direct observation of the neutral hydrogen (H  i) in the intergalactic medium (IGM). In the post-reionization era, this signal instead probes H  i in galaxies, which traces the dark matter density distribution. With new numerical simulations, we investigated the end stages of reionization to elucidate the transition of our Universe into the post-reionization era. Our models are consistent with the latest high-redshift measurements, including ultraviolet (UV) luminosity functions up to redshift |$\simeq$| 8. Notably, these models consistently reproduced the evolution of the UV photon background, which is constrained from Lyman- |$\alpha$| absorption spectra. We studied the dependence of this background on the nature of photon sinks in the IGM, requiring mean free path of UV photons to be |$\sim$| 10 comoving-megaparsecs (cMpc) during the EoR that increases gradually with time during late stages (⁠|$z\lesssim 6$|⁠). Our models revealed that the reionization of the IGM transitioned from an inside-out to an outside-in process when the Universe is less than 0.01 per cent neutral. During this epoch, the 21-cm signal also shifted from probing predominantly the H  i in the IGM to that in galaxies. Furthermore, we identified a statistically significant number of large neutral islands (with sizes up to 40 cMpc) persisting until very late stages (⁠|$5 \lesssim z \lesssim 6$|⁠) that can imprint features in Lyman- |$\alpha$| absorption spectra and also produce a knee-like feature in the 21-cm power spectrum. [ABSTRACT FROM AUTHOR]

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]

Multiple observations now suggest that the hydrogen reionization may have ended well below redshift six. While there has previously been no conclusive proof of extended neutral islands in the |$z \lt 6$| intergalactic medium, it is possible that such islands give rise to the giant Ly  |$\alpha$| absorption troughs seen in the spectra of high-redshift quasars. Here, we present evidence that the deepest and longest known Ly  |$\alpha$| trough at |$z \,\lt\, 6$|⁠ , towards ULAS J0148 + 0600 (J0148), is associated with damping wing absorption. The evidence comes from a window of strong Ly  |$\alpha$| transmission at the edge of the J0148 proximity zone. We show that the relatively smooth profile of this transmission window is highly unlikely to arise from resonant absorption alone, but is consistent with the presence of a damping wing. We further argue that the damping wing is unlikely to arise from a compact source due to the lack of associated metal lines, and is more likely to arise from an extended neutral island associated with the giant Ly  |$\alpha$| trough. We investigate the physical conditions that may give rise to the strong transmission window, and speculate that it may signal an usually deep void, nearby ionizing sources, and/or the recent passage of an ionization front. [ABSTRACT FROM AUTHOR]

Recent quasar absorption line observations suggest that reionization may end as late as |$z \approx 5.3$|⁠. As a means to search for large neutral hydrogen islands at |$z\ \lt\ 6$|⁠ , we revisit long dark gaps in the Ly  |$\beta$| forest in Very Large Telescope/X-Shooter and Keck/Echellette Spectrograph and Imager quasar spectra. We stack the Ly  |$\alpha$| forest corresponding to both edges of these Ly  |$\beta$| dark gaps and identify a damping wing-like extended absorption profile. The average redshift of the stacked forest is |$z=5.8$|⁠. By comparing these observations with reionization simulations, we infer that such a damping wing-like feature can be naturally explained if these gaps are at least partially created by neutral islands. Conversely, simulated dark gaps lacking neutral hydrogen struggle to replicate the observed damping wing features. Furthermore, this damping wing-like profile implies that the volume-averaged neutral hydrogen fraction must be |$\langle x_{\rm H\,{\small {I}}} \rangle \ge 6.1 \pm 3.9~{{\ \rm per\ cent}}$| at |$z = 5.8$|⁠. Our results offer robust evidence that reionization extends below |$z=6$|⁠. [ABSTRACT FROM AUTHOR]

Reionization is thought to be driven by faint star-forming galaxies, but characterizing this population has long remained very challenging. Here, we utilize deep nine-band JADES (JWST Advanced Deep Extragalactic Survey)/NIRCam (Near-Infrared Camera) imaging to study the star-forming and ionizing properties of 756 |$z\sim 6-9$| galaxies, including hundreds of very ultraviolet (UV)-faint objects (⁠|$M_\mathrm{UV}\gt -18$|⁠). The faintest (⁠|$m\sim 30$|⁠) galaxies in our sample typically have stellar masses of |$M_\ast \sim (1-3)\times 10^7\ \mathrm{ M}_\odot$| and young light-weighted ages (⁠|$\sim$| 50 Myr), though some show strong Balmer breaks implying much older ages (⁠|$\sim$| 500 Myr). We find no evidence for extremely massive galaxies (⁠|$\gt 3\times 10^{10}\ \mathrm{ M}_\odot$|⁠) in our sample. We infer a strong (factor |$\gt $| 2) decline in the typical [O  iii ] |$+$| H  |$\beta$| equivalent widths (EWs) towards very faint |$z\sim 6-9$| galaxies, yet a weak UV luminosity dependence on the H  |$\alpha$| EWs at |$z\sim 6$|⁠. We demonstrate that these EW trends can be explained if fainter galaxies have systematically lower metallicities as well as more recently declining star formation histories relative to the most UV-luminous galaxies. Our data provide evidence that the brightest galaxies are frequently experiencing a recent strong upturn in star formation rate. We also discuss how the EW trends may be influenced by a strong correlation between |$M_\mathrm{UV}$| and Lyman continuum escape fraction. This alternative explanation has dramatically different implications for the contribution of galaxies along the luminosity function to cosmic reionization. Finally, we quantify the photometric overdensities around two |$z\,\gt\,7$| strong Ly  |$\alpha$| emitters. One Ly  |$\alpha$| emitter lies close to a strong photometric overdensity, while the other shows no significant nearby overdensity, perhaps implying that not all strong |$z\,\gt\, 7$| Ly  |$\alpha$| emitters reside in large ionized bubbles. [ABSTRACT FROM AUTHOR]

The turbulent ionosphere causes phase shifts to incoming radio waves on a broad range of temporal and spatial scales. When an interferometer is not sufficiently calibrated for the direction-dependent ionospheric effects, the time-varying phase shifts can cause the signal to decorrelate. The ionosphere's influence over various spatiotemporal scales introduces a baseline-dependent effect on the interferometric array. We study the impact of baseline-dependent decorrelation on high-redshift observations with the Low Frequency Array (LOFAR). Data sets with a range of ionospheric corruptions are simulated using a thin-screen ionosphere model, and calibrated using the state-of-the-art LOFAR epoch of reionization pipeline. For the first time ever, we show the ionospheric impact on various stages of the calibration process including an analysis of the transfer of gain errors from longer to shorter baselines using realistic end-to-end simulations. We find that direction-dependent calibration for source subtraction leaves excess power of up to two orders of magnitude above the thermal noise at the largest spectral scales in the cylindrically averaged autopower spectrum under normal ionospheric conditions. However, we demonstrate that this excess power can be removed through Gaussian process regression, leaving no excess power above the 10 per cent level for a |$5~$| km diffractive scale. We conclude that ionospheric errors, in the absence of interactions with other aggravating effects, do not constitute a dominant component in the excess power observed in LOFAR epoch of reionization observations of the North Celestial Pole. Future work should therefore focus on less spectrally smooth effects, such as beam modelling errors. [ABSTRACT FROM AUTHOR]

Radiative transfer (RT) is a crucial ingredient for self-consistent modelling of numerous astrophysical phenomena across cosmic history. However, on-the-fly integration into radiation hydrodynamics (RHD) simulations is computationally demanding, particularly due to the stringent time-stepping conditions and increased dimensionality inherent in multifrequency collisionless Boltzmann physics. The emergence of exascale supercomputers, equipped with extensive CPU cores and GPU accelerators, offers new opportunities for enhancing RHD simulations. We present the first steps towards optimizing arepo - rt for such high-performance computing environments. We implement a novel node-to-node (n-to-n) communication strategy that utilizes shared memory to substitute intranode communication with direct memory access. Furthermore, combining multiple internode messages into a single message substantially enhances network bandwidth utilization and performance for large-scale simulations on modern supercomputers. The single-message n-to-n approach also improves performance on smaller scale machines with less optimized networks. Furthermore, by transitioning all RT-related calculations to GPUs, we achieve a significant computational speedup of around 15 for standard benchmarks compared to the original CPU implementation. As a case study, we perform cosmological RHD simulations of the Epoch of Reionization, employing a similar setup as the THESAN project. In this context, RT becomes sub-dominant such that even without modifying the core arepo codebase, there is an overall threefold improvement in efficiency. The advancements presented here have broad implications, potentially transforming the complexity and scalability of future simulations for a wide variety of astrophysical studies. Our work serves as a blueprint for porting similar simulation codes based on unstructured resolution elements to GPU-centric architectures. [ABSTRACT FROM AUTHOR]

Intensity mapping experiments will soon have surveyed large swathes of the sky, providing information about the underlying matter distribution of our early Universe. The resulting maps can be used to recover statistical information, such as the power spectrum, about the measured spectral lines (for example, H  i , [C  ii ], and [O  iii ]). However precise power spectrum measurements, such as the 21 cm autocorrelation, continue to be challenged by the presence of bright foregrounds and non-trivial systematics. By cross-correlating different data sets, it may be possible to mitigate the effects of both foreground uncertainty and uncorrelated instrumental systematics. Beyond their own merit, cross-correlations could also be used to recover autocorrelation information. Such a technique has been proposed in the literature for recovering the 21 cm power spectrum. Generalizing this result, we develop a statistical framework for combining multiple cross-correlation signals in order to infer information about the corresponding autocorrelations. We do this first within the least squares estimator framework, and show how one can derive their estimator, along with several alternative estimators. We also investigate the posterior distribution of recovered autocorrelation and associated model parameters. We find that for certain noise regimes and cosmological signal modelling assumptions this procedure is effective at recovering autospectra from a set of cross-correlations. Finally, we showcase our framework in the context of several near-future line intensity mapping experiments. [ABSTRACT FROM AUTHOR]

The shape of the low-mass (faint) end of the galaxy stellar mass function (SMF) or ultraviolet luminosity function (UVLF) at |$z \gtrsim 6$| is an open question for understanding which galaxies primarily drove cosmic reionization. Resolved photometry of Local Group low-mass galaxies allows us to reconstruct their star formation histories, stellar masses, and UV luminosities at early times, and this fossil record provides a powerful 'near-far' technique for studying the reionization-era SMF/UVLF, probing orders of magnitude lower in mass than direct HST / JWST observations. Using 882 low-mass (⁠|$M_{\rm star}\lesssim 10^{9}\, \rm {M_\odot }$|⁠) galaxies across 11 Milky Way (MW)- and Local Group-analogue environments from the FIRE-2 cosmological baryonic zoom-in simulations, we characterize their progenitors at |$z=6\!-\!9$|⁠ , the mergers/disruption of those progenitors over time, and how well their present-day fossil record traces the high-redshift SMF. A present-day galaxy with |$M_{\rm star}\sim 10^5\, \rm {M_\odot }$| (⁠|$\sim 10^9\, \rm {M_\odot }$|⁠) had |$\approx 1$| (⁠|$\approx 30$|⁠) progenitors at |$z\approx 7$|⁠ , and its main progenitor comprised |$\approx 100~{{\ \rm per\ cent}}$| (⁠|$\approx 10~{{\ \rm per\ cent}}$|⁠) of the total stellar mass of all its progenitors at |$z\approx 7$|⁠. We show that although only |$\sim 15~{{\ \rm per\ cent}}$| of the early population of low-mass galaxies survives to present day, the fossil record of surviving Local Group galaxies accurately traces the low-mass slope of the SMF at |$z \sim 6 \!-\! 9$|⁠. We find no obvious mass dependence to the mergers and accretion, and show that applying this reconstruction technique to just low-mass galaxies at |$z = 0$| and not the MW/M31 hosts correctly recovers the slope of the SMF down to |$M_{\rm star} \sim 10^{4.5}\, \rm {{\rm M}_{\odot }}$| at |$z \gtrsim 6$|⁠. Thus, we validate the 'near-far' approach as an unbiased tool for probing low-mass reionization-era galaxies. [ABSTRACT FROM AUTHOR]

Patchy reionization generates kinematic Sunyaev–Zel'dovich (kSZ) anisotropies in the cosmic microwave background (CMB). Large-scale velocity perturbations along the line of sight modulate the small-scale kSZ power spectrum, leading to a trispectrum (or four-point function) in the CMB that depends on the physics of reionization. We investigate the challenges in detecting this trispectrum and use tools developed for CMB lensing, such as realization-dependent bias subtraction and cross-correlation based estimators, to counter uncertainties in the instrumental noise and assumed CMB power spectrum. We also find that both lensing and extragalactic foregrounds can impart larger trispectrum contributions than the reionization kSZ signal. We present a range of mitigation methods for both of these sources of contamination, validated on microwave-sky simulations. We use ACT DR6 and Planck data to calculate an upper limit on the reionization kSZ trispectrum from a measurement dominated by foregrounds. The upper limit is about 50 times the signal predicted from recent simulations. [ABSTRACT FROM AUTHOR]

The Voids-within-Voids-within-Voids project used dark-matter-only (DMO) simulations to study the abundance and structure of dark matter (DM) haloes over the full mass range populated in the standard Lambda cold dark matter cosmology. Here, we explore how baryonic effects modify these results for |$z=0$| halo masses in the range |$10^4$| – |$10^7~\mathrm{M_\odot }$|⁠ , below the threshold for galaxy formation. Our main study focuses on three simulations from identical initial conditions at |$z=127$|⁠ , one following DMO, one including non-radiative gas, and one additionally including the baryonic physics relevant in this halo mass range (cooling and photoheating). In the non-radiative simulation, above |$10^{5.5}~\mathrm{M_\odot }$|⁠ , halo abundance and internal structure are very similar to the DMO simulation, and the baryon to DM ratio is everywhere close to the cosmic value. At lower mass, this ratio drops and haloes are less concentrated and less massive in the non-radiative case. Test simulations at higher resolution show this to be mainly a resolution effect; the expected drop in baryon content due to residual pressure effects only becomes substantial for |$z=0$| haloes below |${\sim}10^{2.7}~\mathrm{M_\odot }$|⁠. However, gas is heated by reionization at |$z=6$| in our 'full physics' run, and this results in almost complete expulsion of gas from all haloes in our simulated mass range. This suppresses the halo mass function by |${\sim}30{{\ \rm per\ cent}}$|⁠ , lowers halo concentration, and consequently weakens the DM annihilation signal by |${\sim}40{-}60{{\ \rm per\ cent}}$|⁠. [ABSTRACT FROM AUTHOR]

Observations of 21 cm line from neutral hydrogen promise to be an exciting new probe of astrophysics and cosmology during the Cosmic Dawn and through the Epoch of Reionization (EoR) to when dark energy accelerates the expansion of our Universe. At each of these epochs, separating bright foregrounds from the cosmological signal is a primary challenge that requires exquisite calibration. In this paper, we present a new calibration method called nucal that extends redundant-baseline calibration, allowing spectral variation in antenna responses to be solved for by using correlations between visibilities measuring the same angular Fourier modes at different frequencies. By modelling the chromaticity of the beam-weighted sky with a tunable set of discrete prolate spheroidal sequences, we develop a calibration loop that optimizes for spectrally smooth calibrated visibilities. Crucially, this technique does not require explicit models of the sky or the primary beam. With simulations that incorporate realistic source and beam chromaticity, we show that this method solves for unsmooth bandpass features, exposes narrow-band interference systematics, and suppresses smooth-spectrum foregrounds below the level of 21 cm reionization models, even within much of the so-called wedge region where current foreground mitigation techniques struggle. We show that this foreground subtraction can be performed with minimal cosmological signal loss for certain well-sampled angular Fourier modes, making spectral-redundant calibration a promising technique for current and next-generation 21 cm intensity mapping experiments. [ABSTRACT FROM AUTHOR]

Constraining the escape fraction of Lyman Continuum (LyC) photons from high-redshift galaxies is crucial to understanding reionization. Recent observations have demonstrated that various characteristics of the Ly |$\, \alpha$| emission line correlate with the inferred LyC escape fraction (⁠|$f_{\rm esc}^{\rm LyC}$|⁠) of low-redshift galaxies. Using a data set of 9600 mock Ly |$\, \alpha$| spectra of star-forming galaxies at |$4.64 \le z \le 6$| from the SPHINX |$^{20}$| cosmological radiation hydrodynamical simulation, we study the physics controlling the escape of Ly |$\, \alpha$| and LyC photons. We find that our mock Ly |$\, \alpha$| observations are representative of high-redshift observations and that typical observational methods tend to overpredict the Ly |$\, \alpha$| escape fraction (⁠|$f_{\rm esc}^{\rm Ly\, \alpha }$|⁠) by as much as 2 dex. We investigate the correlations between |$f_{\rm esc}^{\rm LyC}$| and |$f_{\rm esc}^{\rm Ly\, \alpha }$|⁠ , Ly |$\, \alpha$| equivalent width (⁠|$W_{\lambda }({\rm Ly\, \alpha })$|⁠), peak separation (⁠|$v_{\rm sep}$|⁠), central escape fraction (⁠|$f_{\rm cen}$|⁠), and red peak asymmetry (⁠|$A_f^{\rm red}$|⁠). We find that |$f_{\rm esc}^{\rm Ly\, \alpha }$| and |$f_{\rm cen}$| are good diagnostics for LyC leakage, selecting for galaxies with lower neutral gas densities and less UV attenuation that have recently experienced supernova feedback. In contrast, |$W_{\lambda }({\rm Ly\, \alpha })$| and |$v_{\rm sep}$| are found to be necessary but insufficient diagnostics, while |$A_f^{\rm red}$| carries little information. Finally, we use stacks of Ly |$\, \alpha$|⁠ , H |$\, \alpha$|⁠ , and F150W mock surface brightness profiles to find that galaxies with high |$f_{\rm esc}^{\rm LyC}$| tend to have less extended Ly |$\, \alpha$| and F150W haloes but larger H |$\, \alpha$| haloes than their non-leaking counterparts. This confirms that Ly |$\, \alpha$| spectral profiles and surface brightness morphology can be used to better understand the escape of LyC photons from galaxies during the epoch of reionization. [ABSTRACT FROM AUTHOR]

We present new measurements of the mean transmitted flux in the hydrogen |$\rm {Ly\,\alpha }$| and a relative transmitted flux measurement in |$\rm {Ly\,\beta }$| using 27 008 quasar spectra from the Fourteenth Data Release (DR14) of the Extended Baryon Oscillation Spectroscopic Survey. Individual spectra are first combined into 16 composites with mean redshifts in the range of |$2.8\lt z\lt 4.9$|⁠. We then apply Markov Chain Monte Carlo (MCMC) inference to produce a piecewise fit of the effective |$\tau _{\rm {Ly\,\alpha }}$| (corrected for metal lines and optically thick absorption) assuming a spline point distribution. We also perform a relative |$\Delta \tau _{\rm {Ly\,\beta }}$| measurement with the same data set, finding |$\Delta \tau _{\rm {Ly\,\beta }}\lt 0.35$| at |$z\lt 4.8$|⁠. The 6–8  per cent precision measurements in the rest frame 1075–1150 Å at |${\it z} \ \lt \rm {4.0}$| and 10–12 per cent precision measurements in the same region at |${\it z} \ \gt \rm {4.0}$| on |$\tau _{\rm {Ly\,\alpha }}$|⁠ , and our determinations of |$\Delta \tau _{\rm {Ly\,\beta }}$|⁠ , are dominated by systematic errors, likely arising from bias and uncertainties in estimates of the quasar continuum. Our |$\tau _{\rm {Ly\,\alpha }}$| values show a smooth increase by a factor of 5 over the redshift range |$z=2.4-4.4$|⁠. [ABSTRACT FROM AUTHOR]

Spectra of the highest redshift galaxies taken with JWST are now allowing us to see into the heart of the reionization epoch. Many of these observed galaxies exhibit strong damping wing absorption redward of their Lyman- |$\alpha$| emission. These observations have been used to measure the redshift evolution of the neutral fraction of the intergalactic medium and sizes of ionized bubbles. However, these estimates have been made using a simple analytic model for the intergalactic damping wing. We explore the recent observations with models of inhomogeneous reionization from the Sherwood–Relics simulation suite. We carry out a comparison between the damping wings calculated from the simulations and from the analytic model. We find that although the agreement is good on the red side of the Lyman- |$\alpha$| emission, there is a discrepancy on the blue side due to residual neutral hydrogen present in the simulations, which saturates the intergalactic absorption. For this reason, we find that it is difficult to reproduce the claimed observations of large bubble sizes at |$z \sim 7$|⁠ , which are driven by a detection of transmitted flux blueward of the Lyman- |$\alpha$| emission. We suggest instead that the observations can be explained by a model with smaller ionized bubbles and larger intrinsic Lyman- |$\alpha$| emission from the host galaxy. [ABSTRACT FROM AUTHOR]

First stars play crucial roles in the development of the Universe, influencing events like cosmic reionization and the chemcal enrichment of the intergalactic medium. While first stars are conventionally thought to form at around |$z \sim 20$| –30 in the standard |$\Lambda$| cold dark matter (⁠|$\Lambda$| CDM) cosmology, observational constraints on small-scale (⁠|$\\lt $| Mpc) density fluctuations remain limited, possibly differing significantly from the scale-invariant fluctuations assumed in the |$\Lambda $| CDM model. Should this be the case, the formation of first stars could occur much earlier than typically predicted. In this study, we investigate the formation process of first stars in the extremely early epochs of |$z \gtrsim 100$| in the post-recombination Universe. At such early times, the effects of the warm cosmic microwave background (CMB) become significant. We calculate the collapse of primordial star-forming clouds using a one-zone thermo-chemical model that accounts for CMB influences on radiative heating, Compton cooling, and photodissociation reactions. We found that the impact of the CMB on the evolution is limited at |$z \lesssim 100 $|⁠ , with the temperature evolution closely resembling the conventional model. However, within the range |$100 \lesssim z \lesssim 400$|⁠ , the formation of H |$_{2}$| via the H |$^{-}$| channel is impeded by H |$^{-}$| photo-detachment induced by the CMB, leading to higher temperatures compared to standard thermal evolution. Consequently, first stars with masses exceeding |$1000\, {M}_{\odot }$| can emerge at |$z \gtrsim 100$|⁠. Furthermore, at |$z \gtrsim 500$|⁠ , the temperature evolution becomes nearly isothermal at several thousand Kelvin solely due to atomic cooling, as H |$_{2}$| formation is entirely suppressed, including the less-efficient H |$_2^{+}$| channel, which is blocked by H |$_2^{+}$| photodissociation. In such cases, supermassive stars with masses around |$\sim 10^{5}\, {M}_{\odot }$| are expected to form solely via atomic cooling. These findings emphasize the significant variation in the typical mass of the first stars depending on the epoch of formation. [ABSTRACT FROM AUTHOR]

ABSTRACT: The Ly α forest (LAF) at z > 5 probes the thermal and reionization history of the intergalactic medium (IGM) and the nature of dark matter, but its interpretation requires comparison to cosmological hydrodynamical simulations. At high-z, convergence of these simulations is more exacting since transmission is dominated by underdense voids that are challenging to resolve. With evidence mounting for a late end to reionization, small structures down to the sub-kpc level may survive to later times than conventionally thought due to the reduced time for pressure smoothing to impact the gas, further tightening simulation resolution requirements. We perform a suite of simulations using the Eulerian cosmological hydrodynamics code Nyx, spanning domain sizes of 1.25 − 10 h−1 Mpc  and 5 − 80 h−1 kpc  cells, and explore the interaction of these variables with the timing of reionization on the properties of the matter distribution and the simulated LAF at z = 5.5. In observable Ly α power, convergence within 10 per cent is achieved for k < 0.1 s km–1, but larger k shows deviation of up to 20 per cent. While a later reionization retains more small structure in the density field, because of the greater thermal broadening there is little difference in the convergence of LAF power between early (z = 9) and later (z = 6) reionizations. We conclude that at z ∼ 5.5, resolutions of 10 kpc are necessary for convergence of LAF power at k < 0.1 s km–1, while higher-k modes require higher resolution, and that the timing of reionization does not significantly impact convergence given realistic photoheating.

The epoch of reionization (EoR) progressed through the emission of ionizing photons from galaxies to their local intergalactic medium. In this work, we characterize the dwarf star-forming galaxies as candidates for the source of ionizing photons that drove EoR. We investigate the ionizing properties and star formation histories of star-forming dwarf galaxies at the last stages of EoR at |$4.8\lt z \lt 7$| using observations from the CAnadian NIRISS Unbiased Cluster Survey (CANUCS). The magnification due to gravitational lensing allows us to probe large dynamic ranges in stellar mass (⁠|$2\times 10^{6}\le {M}_*/{\rm M}_\odot \le 5\times 10^{9}$|⁠) and ultraviolet (UV) magnitudes (⁠|$-22.68\le M_{\rm UV}\le =-15.95$|⁠). We find a median UV slope |$\beta _{1500}\,$| of |$-2. 56\pm 0.23$| and the production efficiency of ionizing photons |$\log$| |$\xi _{\rm {ion}}\,$| |$=25.39\pm 0.6$| for the full sample (⁠|$4.8\lt z \lt 7$|⁠) with a median stellar mass of |$6.3\pm 0.5\times 10^{7} \, {\rm M}_\odot$|⁠. We find both |$\beta _{1500}\,$| and |$\xi _{\rm {ion}}\,$| are marginally correlated with the stellar mass of the galaxy, indicating a possible greater contribution of dwarf galaxies to the reionization of the Universe. We find that on average, galaxies in our sample are experiencing a recent rise/burst of star formation which translates to a higher scatter in |$\xi _{\rm {ion}}\,$| and a large scatter in H |$\alpha$| equivalent widths (EWs). Finally, we investigate the trends of H |$\alpha$| and [O  iii ] + H |$\beta$| EWs with UV magnitude and find |$M_{\rm UV}$| is correlated between H |$\alpha$| but not with [O  iii ] + H |$\beta$| EWs indicating low metallicities and recent burst in the UV faint galaxies. [ABSTRACT FROM AUTHOR]

Different star formation models at Cosmic Dawn produce detectable signatures in the observables of upcoming 21-cm experiments. In this work, we consider the physical scenario of feedback-free starbursts (FFB), according to which the star formation efficiency (SFE) is enhanced in sufficiently massive haloes at early enough times, thus explaining the indication from the JWST for an excess of bright galaxies at |$z \ge 10$|⁠. We model the contribution of FFBs to popII SFE and compute the impact these have on the 21-cm global signal and power spectrum. We show that FFBs affect the evolution of the brightness temperature and the 21-cm power spectrum, but they only have a limited effect on the neutral hydrogen fraction. We investigate how the observables are affected by changes in the underlying star formation model and by contribution from popIII stars. Finally, we forecast the capability of next-generation Hydrogen Epoch of Reionization Array (HERA) to detect the existence of FFB galaxies via power spectrum measurements. Our results show the possibility of a significant detection, provided that popII stars are the main drivers of lowering the spin temperature. Efficient popIII star formation will make the detection more challenging. [ABSTRACT FROM AUTHOR]

We report the discovery of a compact star-forming galaxy at z = 9.380 in the GOODS-North field (named GN-z9p4), which shows numerous strong UV-optical emission lines and a single UV line, N IV] λ1486. This makes GN-z9p4 the third-highest redshift N-emitter known to date. We determined the nebular abundances of H, C, N, O and Ne, along with the size and other physical properties of this object, then compared them to those of the other N-emitters known so far and to other star-forming galaxies. Using the direct method, we found a metallicity of 12 + log(O/H) = 7.37 ± 0.15, which stands as one of the lowest among N-emitters. The N/O abundance ratio is highly super-solar, while C/O and Ne/O are normal compared to other galaxies at low metallicity. We show that the compactness of GN-z9p4 (with an effective radius of 118 ± 16 pc at 2 μm) and other N-emitters translates to very high stellar mass and star formation rate (SFR) surface densities, which could serve as a criterium for identifying other N-emitters. Future studies and larger samples are needed to understand these rare, and enigmatic objects that have only recently been discovered. [ABSTRACT FROM AUTHOR]

Context. The redshifted 21 cm signal from the Epoch of Reionization (EoR) directly probes the ionization and thermal states of the intergalactic medium during that period. In particular, the distribution of the ionized regions around the radiating sources during EoR introduces scale-dependent features in the spherically averaged EoR 21 cm signal power spectrum. Aims. The goal is to study these scale-dependent features at different stages of reionization using numerical simulations and to build a source model-independent framework to probe the properties of the intergalactic medium using EoR 21 cm signal power spectrum measurements. Methods. Under the assumption of high spin temperature, we modeled the redshift evolution of the ratio of the EoR 21 cm brightness temperature power spectrum to the corresponding density power spectrum using an ansatz consisting of a set of redshift and scale-independent parameters. This set of eight parameters probes the redshift evolution of the average ionization fraction and the quantities related to the morphology of the ionized regions. Results. We tested this ansatz on different reionization scenarios generated using different simulation algorithms and found that it is able to recover the redshift evolution of the average neutral fraction within an absolute deviation ≲0.1. Conclusions. Our framework allows us to interpret 21 cm signal power spectra in terms of parameters related to the state of the IGM. This source model-independent framework is able to efficiently constrain reionization scenarios using multi-redshift power spectrum measurements with ongoing and future radio telescopes such as LOFAR, MWA, HERA, and SKA. This will add independent information regarding the EoR IGM properties. [ABSTRACT FROM AUTHOR]

Recent observations with the James Webb Space Telescope (JWST) have further refined the spectroscopic redshift of GN-z11, one of the most distant galaxies identified with the Hubble Space Telescope, at z = 10.603. The presence of extremely dense gas (> 1010 cm−3), the detection of high-ionisation lines and of CII*1335 emission, and the presence of an ionisation cone indicate that GN-z11 also hosts an active galactic nucleus. Further photometric and spectroscopic follow-up demonstrates that it lies in a large-scale, overdense structure with possible signatures of Population III stars in its halo. Surprisingly, Lyα has also been detected despite the expected largely neutral intergalactic medium at such a redshift. We exploit recent JWST/NIRSpec integral field unit observations to demonstrate that the Lyα emission in GN-z11 is part of an extended halo with a minimum size of 0.8–3.2 kpc, depending on the definition used to derive the halo size. The surface brightness of the Lyα halo around GN-z11 appears consistent with Lyα halos observed around z ∼ 6 quasars. At the wavelength of Lyα at z ∼ 10.6, we identify three other emission line candidates within the integral field unit field of view with no UV rest-frame counterpart visible in deep images from the JWST/NIRCam. If confirmed, this could be the first evidence that the local region of GN-z11 represents a candidate protocluster core, forming just 400 Myr after the Big Bang. We give a first estimate of the dark matter halo mass of this structure (Mh = 2.96−0.39+0.44 × 1010 M⊙), which is consistent with a Coma-like cluster progenitor. [ABSTRACT FROM AUTHOR]

We present a study on stellar properties of Lyman-alpha (Ly α) emitters at 5 < z < 8.2. We use 247 photometrically selected, lensed, high-redshift, low-luminosity galaxy candidates with spectroscopic follow-up. Of these, 38 are confirmed spectroscopically to be between 5 < z < 8.2 via detection of Ly α. For each galaxy and candidate, we estimate stellar mass, star formation rate, specific star formation rate, and mass-weighted age with spectral energy distribution fitting. We also measure the UV β slope and luminosity using values from photometry. We find no strong correlation between Ly α equivalent width and any of these properties, as well as no significant difference between the physical properties of Ly α emitters and candidates without Ly α detected. This lack of expected trends may be explained by a combination of the evolving opacity of the intergalactic medium at these redshifts as well as the unique phase space probed by our lensed sample. Via tests on other galaxy samples which show varying strengths of correlations, we conclude that if there exist any relationships between Ly α equivalent width and physical properties in the underlying population of faint galaxies, they are weak correlations. We also present the results of a spectroscopic search for C  iii ] emission in confirmed Ly α emitters at z ∼ 7, finding no C  iii ] detections, but putting constraints on strong active galactic nuclei activity and extreme nebular emission. [ABSTRACT FROM AUTHOR]

An important characteristic of cosmic hydrogen reionization is the growth of ionized gas bubbles surrounding early luminous objects. Ionized bubble sizes are beginning to be probed using Lyman α emission from high-redshift galaxies, and will also be probed by upcoming 21 cm maps. We present results from a study of bubble sizes using the state-of-the-art thesan radiation-hydrodynamics simulation suite, which self-consistently models radiation transport and realistic galaxy formation. We employ the mean free path method and track the evolution of the effective ionized bubble size at each point (R eff) throughout the Epoch of Reionization. We show that there is a slow growth period for regions ionized early, but a rapid 'flash ionization' process for regions ionized later as they immediately enter a large, pre-existing bubble. We also find that bright sources are preferentially in larger bubbles, and find consistency with recent observational constraints at z ≳ 9, but tension with idealized Lyman α damping-wing models at z ≈ 7. We find that high-overdensity regions have larger characteristic bubble sizes, but the correlation decreases as reionization progresses, likely due to runaway formation of large percolated bubbles. Finally, we compare the redshift at which a region transitions from neutral to ionized (z reion) with the time it takes to reach a given bubble size and conclude that z reion is a reasonable local probe of small-scale bubble size statistics (⁠|$R_\text{eff} \lesssim 1\, \rm {cMpc}$|⁠). However, for larger bubbles, the correspondence between z reion and size statistics weakens due to the time delay between the onset of reionization and the expansion of large bubbles, particularly at high redshifts. [ABSTRACT FROM AUTHOR]