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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]

We present JWST/NIRSpec prism spectroscopy of MACS0647−JD, a triply lensed z ∼ 11 candidate discovered in Hubble Space Telescope imaging and spatially resolved by JWST imaging into two components, A and B. Spectroscopy of component A yields a spectroscopic redshift z = 10.17 based on seven detected emission lines: C iii ] λ λ 1907, 1909, [O ii ] λ 3727, [Ne iii ] λ 3869, [Ne iii ] λ 3968, H δ λ 4101, H γ λ 4340, and [O iii ] λ 4363. These are the second-most distant detections of these emission lines to date, in a galaxy observed just 460 million years after the Big Bang. Based on observed and extrapolated line flux ratios we derive a gas-phase metallicity 12 + log(O/H) ∼ 7.5–8.0, or Z ∼ (0.06–0.2) Z ⊙, ionization parameter log (U) = −1.9 ± 0.2, and an ionizing photon production efficiency log (ξ ion) = 25.2 ± 0.2 erg−1 Hz. The spectrum has a softened Ly α break, evidence for a strong Ly α damping wing. The Ly α damping wing also suppresses the F150W photometry, explaining the slightly overestimated photometric redshift z = 10.6 ± 0.3. MACS0647−JD has a stellar mass log(M / M ⊙) = 8.1 ± 0.3, including ∼6 × 107 M ⊙ in component A, most of which formed recently (within ∼20 Myr) with a star formation rate ∼ 2 ± 1 M ⊙ yr−1, all within an effective radius 70 ± 24 pc. Spectroscopy of a fainter companion galaxy C separated by a distance of ∼ 3 kpc reveals a Lyman break consistent with z ∼ 10.17. MACS0647−JD is likely the most distant galaxy merger known. [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]

We report the detection of Lyman-continuum (LyC) photons from a massive interacting system at z = 1.097 in the Hubble Ultra Deep Field. The LyC detection is made in the far-ultraviolet F154W band of the UVIT telescope on board AstroSat. Both JWST and Hubble Space Telescope (HST) imaging of the system reveal signs that it is a likely merger. In particular, high-resolution imaging in the JWST bands reveals an infrared-luminous object within the system that is faint in the bluer HST bands. The ionized gas kinematics from the MUSE-UDF data supports the merger hypothesis. We estimate that the entire system is leaking more than 8% of its ionizing photons to the intergalactic medium. The spectral-energy-distribution-derived stellar masses of the two components indicate that this is a major merger with a mass ratio of 1.13 ± 0.37. This detection hints at the potential contribution of massive interacting systems at higher redshifts, when major mergers were more frequent, to the ionizing budget of the Universe. [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]

We present volume-averaged neutral hydrogen fractions x H I and ionized bubble radii R b measured with Ly α damping wing absorption of galaxies at the epoch of reionization. We combine JWST/NIRSpec spectra taken by the CEERS, GO-1433, DDT-2750, and JADES programs and obtain a sample containing 27 bright UV-continuum (M UV < −18.5 mag) galaxies at 7 < z < 12. We construct four composite spectra binned by redshift and find the clear evolution of the softening break toward high redshift at rest-frame 1216 Å, suggesting an increase of Ly α damping wing absorption. We estimate Ly α damping wing absorption in the galaxy spectra with realistic templates including Ly α emission and circumgalactic medium absorptions. Assuming the standard inside-out reionization picture having an ionized bubble with radius R b around a galaxy embedded in the intergalactic medium with x H I, we obtain x H I (R b) values generally increasing (decreasing) from x H I = 0.53 − 0.47 + 0.18 to 0.92 − 0.10 + 0.08 ( log R b = 1.67 − 0.16 + 0.14 to − 0.69 − 0.24 + 0.89 comoving Mpc) at redshift 7.12 − 0.08 + 0.06 to 9.91 − 1.15 + 1.49 . The redshift evolution of x H I indicates a moderately late reionization history consistent with the one previously suggested from the electron scattering of cosmic microwave background and the evolution of UV luminosity function with an escape fraction f esc ∼ 0.2. Our R b measurements suggest that bubble sizes could be up to a few dex larger than the cosmic average values estimated by analytic calculations for a given x H I, while our R b measurements are roughly comparable with the values for merged ionized bubbles around bright galaxies predicted by recent numerical 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]

Ultraviolet (UV; rest-frame ∼1200–2000 Å) spectra provide a wealth of diagnostics to characterize fundamental galaxy properties, such as their chemical enrichment, the nature of their stellar populations, and their amount of Lyman-continuum (LyC) radiation. In this work, we leverage publicly released JWST data to construct the rest-frame UV-to-optical composite spectrum of a sample of 63 galaxies at 5.6 < z < 9, spanning a wavelength range from 1500 to 5200 Å. Based on the composite spectrum, we derive an average dust attenuation E (B − V) gas = 0.10 − 0.11 + 0.10 from H β /H γ, an electron density n e = 570 − 290 + 510 cm−3 from the [O ii ] doublet ratio, an electron temperature T e = 16700 − 1500 + 1500 K from the [O iii ] λ 4363/[O iii ] λ 5007 ratio, and an ionization parameter log (U) = − 2.15 − 0.03 + 0.03 from the [O iii ]/[O ii ] ratio. Using a direct T e method, we calculate an oxygen abundance 12 + log (O / H) = 7.67 ± 0.08 and a carbon-to-oxygen (C/O) abundance ratio log (C / O) = − 0.86 − 0.10 + 0.13 . This C/O ratio is smaller than compared to z = 0 and z = 2–4 star-forming galaxies, albeit with moderate significance. This indicates the reionization-era galaxies might be undergoing a rapid buildup of stellar mass with high specific star formation rates. A UV diagnostic based on the ratios of C iii ] λ λ 1907, 1909/He ii λ 1640 versus O iii ] λ 1666/He ii λ 1640 suggests that the star formation is the dominant source of ionization, similar to the local extreme dwarf galaxies and z ∼ 2–4 He ii –detected galaxies. The [O iii ]/[O ii ] and C iv /C iii ] ratios of the composite spectrum are marginally larger than the criteria used to select galaxies as LyC leakers, suggesting that some of the galaxies in our sample are strong contributors to the reionizing radiation. [ABSTRACT FROM AUTHOR]

The key to detecting neutral hydrogen during the epoch of reionization (EoR) is to separate the cosmological signal from the dominating foreground radiation. We developed direct optimal mapping (DOM) to map interferometric visibilities; it contains only linear operations, with full knowledge of point spread functions from visibilities to images. Here, we demonstrate a fast Fourier transform-based image power spectrum and its window functions computed from the DOM images. We use noiseless simulation, based on the Hydrogen Epoch of Reionization Array Phase I configuration, to study the image power spectrum properties. The window functions show <10−11 of the integrated power leaks from the foreground-dominated region into the EoR window; the 2D and 1D power spectra also verify the separation between the foregrounds and the EoR. [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]

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 characterize the earliest galaxy population in the JADES Origins Field, the deepest imaging field observed with JWST. We make use of ancillary Hubble Space Telescope optical images (five filters spanning 0.4–0.9 μ m) and novel JWST images with 14 filters spanning 0.8−5 μ m, including seven medium-band filters, and reaching total exposure times of up to 46 hr per filter. We combine all our data at >2.3 μ m to construct an ultradeep image, reaching as deep as ≈31.4 AB mag in the stack and 30.3–31.0 AB mag (5 σ, r = 0.″1 circular aperture) in individual filters. We measure photometric redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts z = 11.5−15. These objects show compact half-light radii of R 1/2 ∼ 50−200 pc, stellar masses of M ⋆ ∼ 107−108 M ☉, and star formation rates ∼ 0.1−1 M ☉ yr−1. Our search finds no candidates at 15 < z < 20, placing upper limits at these redshifts. We develop a forward-modeling approach to infer the properties of the evolving luminosity function without binning in redshift or luminosity that marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the impact of nondetections. We find a z = 12 luminosity function in good agreement with prior results, and that the luminosity function normalization and UV luminosity density decline by a factor of ∼2.5 from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical models for evolution of the dark matter halo mass function. [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]

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]

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. [ABSTRACT FROM AUTHOR]

We present SPICE , a new suite of radiation-hydrodynamic, cosmological simulations targeting the epoch of reionization. The goal of these simulations is to systematically probe a variety of stellar feedback models, including 'bursty' and 'smooth' forms of supernova energy injection, as well as poorly explored physical scenarios such as hypernova explosions and radiation pressure on dust. We show that even subtle differences in the behaviour of supernova feedback drive profound differences in reionization histories, with burstier forms of feedback causing earlier reionization. However, we also find that some global galaxy properties, such as the dust-attenuated luminosity functions and star formation main sequence, remain degenerate between models. In particular, we show that stellar feedback and its strength determine the morphological mix of galaxies emerging by |$z \, = \, 5$| and that the reionization history is inextricably connected to intrinsic properties such as galaxy kinematics and morphology. While star-forming, massive discs are prevalent if supernova feedback is 'smooth', 'bursty' feedback preferentially generates dispersion-dominated systems. Different modes of feedback produce different strengths of outflows, altering the interstellar/circumgalactic medium in different ways, and in turn strongly affecting the escape of Lyman continuum (LyC) photons. We establish a correlation between galaxy morphology and LyC escape fraction, revealing that dispersion-dominated systems have escape fractions 10–50 times higher than their rotation-dominated counterparts at all redshifts. At the same intrinsic luminosity, dispersion-dominated systems should thus preferentially generate large H  ii regions as compared to their rotation-dominated counterparts. Since dispersion-dominated systems are more prevalent if stellar feedback is more explosive, reionization occurs earlier in our simulation with burstier feedback. We argue that statistical samples of post-reionization galaxy morphologies (using both stellar and gaseous components) probed with telescopes such as JWST , ALMA, and MUSE can constrain stellar feedback at z > 5 and models of cosmic reionization. [ABSTRACT FROM AUTHOR]

By using an ultradeep JWST/MIRI image at 5.6 μ m in the Hubble eXtreme Deep Field, we constrain the role of strong H α emitters (HAEs) during "cosmic reionization" at z ≃ 7–8. Our sample of HAEs is comprised of young (<35 Myr) galaxies, except for one single galaxy (≈300 Myr), with low stellar masses (≲109 M ⊙). These HAEs show a wide range of rest-frame UV continuum slopes (β), with a median value of β = −2.15 ± 0.21, which broadly correlates with stellar mass. We estimate the ionizing photon production efficiency (ξ ion,0) of these sources (assuming f esc,LyC = 0%), which yields a median value log 10 (ξ ion , 0 / (Hz erg − 1)) = 25.50 − 0.12 + 0.10 . We show that ξ ion,0 positively correlates with H α equivalent width and specific star formation rate. Instead ξ ion,0 weakly anticorrelates with stellar mass and β. Based on the β values, we predict f esc , LyC = 4 % − 2 + 3 , which results in log 10 (ξ ion / (Hz erg − 1)) = 25.55 − 0.13 + 0.11 . Considering this and related findings from the literature, we find a mild evolution of ξ ion with redshift. Additionally, our results suggest that these HAEs require only modest escape fractions (f esc,rel) of 6%–15% to reionize their surrounding intergalactic medium. By only considering the contribution of these HAEs, we estimated their total ionizing emissivity ( N ̇ ion ) as N ̇ ion = 10 50.53 ± 0.45 s − 1 Mpc − 3 . When comparing their N ̇ ion with non-HAE galaxies across the same redshift range, we find that that strong, young, and low-mass emitters may have played an important role during cosmic reionization. [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.

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]

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]

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]

The H i 21 cm global signal from the Cosmic Dawn and the Epoch of Reionization (EoR) offers critical insights into the evolution of our Universe. Yet, its detection presents significant challenges, due to its extremely low signal-to-contamination ratio and complex instrumental systematics. In this paper, we examine the effects of the ionosphere and antenna beam on data analysis. The ionosphere, an ionized plasma layer in the Earth's atmosphere, refracts, absorbs, and emits radio waves in the relevant frequency range. This interaction results in additional spectral distortion of the observed signal, complicating the process of foreground subtraction. Additionally, chromatic variations in the beam can also introduce further contamination into the global spectrum measurement. Notably, the ionospheric effect, being dependent on the direction of incoming light, interacts with the instrumental beam, adding another layer of complexity. To address this, we evaluate three different fitting templates of foreground: the logarithmic polynomial, the physically motivated Experiment to Detect the Global EoR Signature (EDGES) template, and a singular value decomposition (SVD)-based template. Our findings indicate that the EDGES and SVD templates generally surpass logarithmic polynomials in performance. Recognizing the significance of beam chromaticity, we further investigate specific beam distortion models and their impacts on the signal extraction process. [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]

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]