Reionization Research Articles

Improving H2RG Performance in SPHEREx Brassboard Model

Abstract Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer is an upcoming NASA satellite mission to study the physics of inflation, the history of galaxy formation, and the abundance of biogenic ices in the Milky Way, obtaining the first all-sky spectroscopic survey at infrared wavelengths 0.75–5.0 μm. The instrument implements HAWAII-2RG (H2RG) detectors and custom-built Video8 electronics with multiple sampling features to optimize the H2RG noise performance, including nonsequential row reads, voltage monitoring, multiple visits to optically dark reference pixels, as well as onboard slope fitting and cosmic-ray removal. We report here the performance of a single H2RG with the readout electronics. We focus on the effectiveness of multiple reference samplings to reduce 1/f noise most relevant to the galaxy formation analysis, in particular the noise on large angular scales k <0.13 [pix−1] (∼5″–20″) where the imprints of galaxy clustering will be measured. Our characterization confirms that increased sampling of reference pixels successfully reduces the 1/f noise by ∼50% at these scales. However, the effectiveness of multiple reference reads is limited by irreducible per-pixel telegraph noise. Further noise reduction can be achieved by using optical pixels in addition to the reference pixels to remove common-mode signal offsets in each channel. Additionally, we observe that the gain of optical pixels is consistently ∼90% that of the reference pixels, prompting additional correction steps in the data reduction pipeline.

NuSTAR Observations of a Varying-flux Quasar in the Epoch of Reionization

Abstract With enough X-ray flux to be detected in a 160 s scan by SRG/eROSITA, the z = 6.19 quasar CFHQS J142952+544717 is, by far, the most luminous X-ray source known at z > 6. We present deep (245 ks) NuSTAR observations of this source; with ∼180 net counts in the combined observations, CFHQS J142952+544717 is the most distant object ever observed by the observatory. Fortuitously, this source was independently observed by Chandra ∼110 days earlier, enabling the identification of two nearby (30″ and 45″ away), fainter X-ray sources. We jointly fit both Chandra and NuSTAR observations—self-consistently including interloper sources—and find that, to greater than 90% confidence, the observed 3–7 keV flux varied by a factor of ∼2.6 during that period, corresponding to approximately two weeks in the quasar rest frame. This brightening is one of the most extreme instances of statistically significant X-ray variability seen in the Epoch of Reionization. We discuss possible scenarios that could produce such rapid change, including X-ray emission from jets too faint at radio frequencies to be observed.

Rising from the ashes: evidence of old stellar populations and rejuvenation events in the very early Universe

Abstract While JWST has observed galaxies assembling as early as $z\sim 14$, evidence of galaxies with significant old stellar populations in the Epoch of Reionization (EoR) – the descendants of these earliest galaxies – are few and far between. Bursty star-formation histories (SFHs) have been invoked to explain the detectability of the earliest UV-bright galaxies, but also to interpret galaxies showing Balmer breaks without nebular emission lines. We present the first spectroscopic evidence of a $z\sim 7.9$ galaxy, A2744-YD4, which shows a Balmer break and emission lines, indicating the presence of both a mature and young stellar population. The spectrum of A2744-YD4 shows peculiar emission line ratios suggesting a relatively low ionization parameter and high gas-phase metallicity. A median stack of galaxies with similar emission line ratios reveals a clear Balmer break in their stacked spectrum. This suggests that a mature stellar population (∼80 Myr old) has produced a chemically enriched, disrupted interstellar medium. Based on SED-fitting and comparison to simulations, we conclude that the observed young stellar population is in fact the result of a rejuvenation event following a lull in star formation lasting ∼20 Myr, making A2744-YD4 and our stack the first spectroscopic confirmation of galaxies that have rejuvenated following a mini-quenched phase. These rejuvenating galaxies appear to be in an exceptional evolutionary moment where they can be identified. Our analysis shows that a young stellar population of just ∼30 per cent of the total stellar mass would erase the Balmer break. Hence, ‘outshining’ through bursty SFHs in early galaxies is likely plaguing attempts to measure their stellar ages and masses accurately.

Probing dark relativistic species and their interactions with dark matter through CMB and 21 cm surveys

We investigate the sensitivity of the 21 cm power spectrum from cosmic dawn and the epoch of reionization to models of free-streaming dark radiation (parameterized through N eff) and interacting dark radiation-dark matter models (DM-DR). The latter models have gained attention for their potential in addressing recent cosmological tensions and structure formation challenges.We perform a Fisher matrix analysis under different assumptions regarding the astrophysical modeling, and forecast the sensitivity of HERA observations, combined with CMB data from Planck and the Simons Observatory (SO), to N eff and DM-DR interaction modeled using the ETHOS framework assuming a constant scattering rate between the two components.Most importantly, we find that 21 cm observations can improve the sensitivity to the DM-DR interaction rate by up to four order of magnitude compared to Planck and SO. Conversely, in the limit of low interaction rate (which asymptotically matches N eff), CMB data dominates the constraining power, but the inclusion of HERA data can provide a ∼ 20% improvement in sensitivity over CMB data alone.Moreover, we find that HERA observations will be able to probe a region of the DM-DR interaction parameter space which is promising to explain the weak lensing amplitude `S 8' tension. Our results demonstrate the complementarity of 21 cm and CMB data in exploring dark sector interactions.

Probing dark energy using anisotropies in the clustering of post-EoR H i distribution

We propose an anisotropy quantifier of the H i 21-cm signal traditionally used to clock the astrophysics of the reionization era as a post-reionization dark energy diagnostic. We find that the anisotropy probe can be measured at SNR ∼ 10 in both auto-correlation and in cross-correlation with the Ly-α forest over a wide z and k-range. We propose to use the BAO signature on the anisotropy signal to measure ( H(z), DA (z)). Subsequently, we put constraints on a dark energy model involving a negative cosmological constant on top of a quintessence scalar field and find that such a model is consistent with futuristic observations.

UNCOVER: Candidate Red Active Galactic Nuclei at 3 < z < 7 with JWST and ALMA

The James Webb Space Telescope (JWST) is revolutionizing our knowledge of z > 5 galaxies and their actively accreting black holes. Using the JWST Cycle 1 Treasury program Ultradeep NIRSpec and NIRCam Observations before the Epoch of Reionization (UNCOVER) in the lensing field A2744, we report the identification of a sample of little red dots at 3 < z phot < 7 that likely contain highly reddened accreting supermassive black holes. Using a NIRCam-only selection to F444W < 27.7 mag, we find 26 sources over the ∼45 arcmin2 field that are blue in F115W − F200W ∼ 0 (or β UV ∼ –2.0 for f λ ∝ λ β ), red in F200W − F444W = 1−4 (β opt ∼ +2.0), and are dominated by a point-source-like central component. Of the 20 sources with deep Atacama Large Millimeter/submillimeter Array (ALMA) 1.2 mm coverage, none are detected individually or in a stack. For the majority of the sample, spectral energy distribution fits to the JWST+ALMA observations prefer models with hot dust rather than obscured star formation to reproduce the red NIRCam colors and ALMA 1.2 mm nondetections. While compact dusty star formation cannot be ruled out, the combination of extremely small sizes (〈r e 〉 ≈ 50 pc after correction for magnification), red rest-frame optical slopes, and hot dust can be explained by reddened broad-line active galactic nuclei (AGNs). Our targets have faint M 1450 ≈ −14 to −18 mag but inferred bolometric luminosities of L bol = 1043–1046 erg s−1, reflecting their obscured nature. If the candidates are confirmed as AGNs with upcoming UNCOVER spectroscopy, then we have found an abundant population of reddened luminous AGNs that are at least ten times more numerous than UV-luminous AGNs at the same intrinsic bolometric luminosity.

Beyond the horizon: Quantifying the full sky foreground wedge in the cylindrical power spectrum

One of the main obstacles preventing the detection of the redshifted 21 cm signal from neutral hydrogen in the early Universe is the astrophysical foreground emission, which is several orders of magnitude brighter than the signal. The foregrounds, due to their smooth spectra, are expected to predominantly occupy a region in the cylindrical power spectrum known as the foreground wedge. However, the conventional equations describing the extent of the foreground wedge are derived under a flat-sky approximation. This assumption breaks down for tracking wide-field instruments, thus rendering these equations inapplicable in these situations. In this paper we derive equations for the full sky foreground wedge, and show that the foregrounds can potentially extend far beyond what the conventional equations suggest. We also derive the equations that describe a specific bright source in the cylindrical power spectrum space. The validity of both sets of equations is tested against numerical simulations. Many current and upcoming interferometers (e.g., LOFAR, NenuFAR, MWA, SKA) are wide-field phase-tracking instruments. These equations give us new insights into the nature of foreground contamination in the cylindrical power spectra estimated using wide-field instruments. Additionally, they allow us to accurately associate features in the power spectrum with foregrounds or instrumental effects. The equations are also important for correctly selecting the epoch of reionization (EoR) window for foreground avoidance analyses, and for planning 21 cm observations. In future analyses, we recommend using these updated horizon lines to indicate the foreground wedge in the cylindrical power spectrum accurately. The new equations for generating the updated wedge lines are made available in the Python library pslines

A dormant overmassive black hole in the early Universe

Recent observations have found a large number of supermassive black holes already in place in the first few hundred million years after the Big Bang, many of which seem to be overmassive relative to their host galaxy stellar mass when compared with local relation1, 2, 3, 4, 5, 6, 7, 8–9. Several different models have been proposed to explain these findings, ranging from heavy seeds to light seeds experiencing bursts of high accretion rate10, 11, 12, 13, 14, 15–16. Yet, current datasets are unable to differentiate between these various scenarios. Here we report the detection, from the JADES survey, of broad Hα emission in a galaxy at z = 6.68, which traces a black hole with a mass of about 4 × 108M⊙ and accreting at a rate of only 0.02 times the Eddington limit. The black hole to host galaxy stellar mass ratio is about 0.4—that is, about 1,000 times above the local relation—whereas the system is closer to the local relations in terms of dynamical mass and velocity dispersion of the host galaxy. This object is most likely an indication of a much larger population of dormant black holes around the epoch of reionization. Its properties are consistent with scenarios in which short bursts of super-Eddington accretion have resulted in black hole overgrowth and massive gas expulsion from the accretion disk; in between bursts, black holes spend most of their life in a dormant state.

A blazar in the epoch of reionization

AbstractRelativistic jets are thought to play a crucial role in the formation and evolution of massive galaxies and supermassive black holes. Blazars, which are quasars with jets aligned along our line of sight, provide insights into the jetted population and have been observed up to redshifts of z = 6.1. Here, we report the discovery and multi-wavelength characterization of the blazar VLASS J041009.05−013919.88 at z = 7 (age of the Universe ~750 Myr), which is powered by a ~7 × 108 M⊙ black hole. The presence of this high-redshift blazar implies a large population of similar but unaligned jetted sources in the early Universe. Our findings suggest two possible scenarios. In one, the jet in J0410−0139 is intrinsically low power but appears highly luminous due to relativistic beaming, suggesting that most ultraviolet-bright quasars at this redshift host jets. Alternatively, if J0410−0139 represents an intrinsically powerful radio source, there should be hundreds to thousands of radio-quiet quasars at z ≈ 7 with properties like those of J0410−0139, a prediction in tension with observed quasar densities based on their ultraviolet luminosity function. These results support the hypothesis that the rapid growth of black holes in the early Universe may be driven by jet-enhanced or obscured super-Eddington accretion, potentially playing a key role in forming massive black holes during the epoch of reionization.

Neutral fraction of hydrogen in the intergalactic medium surrounding high-redshift gamma-ray burst 210905A

ABSTRACT The Epoch of Reionization (EoR) is a key period of cosmological history in which the intergalactic medium (IGM) underwent a major phase change from being neutral to almost completely ionized. Gamma-ray bursts (GRBs) are luminous and unique probes of their environments that can be used to study the timeline for the progression of the EoR. Here, we present a detailed analysis of the European Southern Observatory Very Large Telescope X-shooter spectrum of GRB 210905A, which resides at a redshift of $z\sim 6.3$. We focus on estimating the fraction of neutral hydrogen, $x_{\rm H \, {\small I}}$, on the line of sight to the host galaxy of GRB 210905A by fitting the shape of the Lyman-$\alpha$ damping wing of the afterglow spectrum. The X-shooter spectrum has a high signal-to-noise ratio, but the complex velocity structure of the host galaxy limits the precision of our conclusions. The statistically preferred model suggests a low neutral fraction with a 3$\sigma$ upper limit of $x_{\rm H \, {\small I}} \lesssim 0.15$ or $x_{\rm H \, {\small I}} \lesssim 0.23$, depending on the absence or presence of an ionized bubble around the GRB host galaxy, indicating that the IGM around the GRB host galaxy is mostly ionized. We discuss complications in current analyses and potential avenues for future studies of the progression of the EoR and its evolution with redshift.

Atomic and molecular gas as traced by [C II] emission

The latest ALMA and JWST observations provide new information on the birth and evolution of galaxies in the early Universe at the epoch of reionization. Measurements at redshift $ z &gt; 5$ of their cold-gas budget are particularly important because this budget is known to be the main fuel for star formation. A powerful tool for probing the physics characterising galaxies at high redshift is the m$ emission line. Due to its low excitation potential emission can be produced in photodissociation regions, neutral atomic gas, and molecular clouds. To properly capture the cold-gas processes taking place in these environments (molecule formation, self-shielding, dust grain catalysis, and photoelectric and cosmic-ray heating), we made use of a new set of dedicated hydrodynamic simulations ( including time-dependent non-equilibrium chemistry, star formation, stellar evolution, metal spreading, and feedback mechanisms. We were able to accurately track the evolution of and H$_2$ in a cosmological context and predict the contribution of each gas phase to luminosity. We provide formulas that can be used to estimate the mass of molecular and atomic gas from detections. Furthermore, we analysed the evolution of conversion factors with galactic properties, such as stellar metallicity, star formation rate, and stellar mass. We demonstrate that emission is dominated by gas and that most of the luminosity is generated in warm, dense, star-forming regions. We conclude that although predominantly traces atomic rather than molecular gas, the luminosity remains a robust indicator of the H$_2$ mass.

Reionization relics in the cross-correlation between the Lyα forest and 21 cm intensity mapping in the post-reionization era

Abstract 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 endeavors 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 Lyα forest and 21 cm intensity mapping, accounting for the repercussions of inhomogeneous reionization in the post-reionization era. We investigate the ability of SKA × DESI-like, SKA × MUST-like, and PUMA × MUST-like instrumental setups to achieve a high signal-to-noise ratio (SNR) in the redshift range 3.5 ≤ z ≤ 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 × MUST-like setup, with a modest 100-hour integration time over a 100 sq. deg. survey, to constrain the ionization efficiency error to σζ = 3.42.

FlexRT — A fast and flexible cosmological radiative transfer code for reionization studies. Part I. Code validation

The wealth of high-quality observational data from the epoch of reionization that will become available in the next decade motivates further development of modeling techniques for their interpretation. Among the key challenges in modeling reionization are (1) its multi-scale nature, (2) the computational demands of solving the radiative transfer (RT) equation, and (3) the large size of reionization's parameter space. In this paper, we present and validate a new RT code designed to confront these challenges. FlexRT (Flexible Radiative Transfer) combines adaptive ray tracing with a highly flexible treatment of the intergalactic ionizing opacity. This gives the user control over how the intergalactic medium (IGM) is modeled, and provides a way to reduce the computational cost of a FlexRT simulation by orders of magnitude while still accounting for small-scale IGM physics. Alternatively, the user may increase the angular and spatial resolution of the algorithm to run a more traditional reionization simulation. FlexRT has already been used in several contexts, including simulations of the Lyman-α forest of high-z quasars, the redshifted 21cm signal from reionization, as well as in higher resolution reionization simulations in smaller volumes. In this work, we motivate and describe the code, and validate it against a set of standard test problems from the Cosmological Radiative Transfer Comparison Project. We find that FlexRT is in broad agreement with a number of existing RT codes in all of these tests. Lastly, we compare FlexRT to an existing adaptive ray tracing code to validate FlexRT in a cosmological reionization simulation.

A resolved Lyman α profile with doubly peaked emission at z ∼ 7

Context. The epoch of reionization is a landmark in structure formation and galaxy evolution. How it happened is still not clear, especially regarding which population of objects was responsible for contributing the bulk of ionizing photons to this process. Doubly peaked Lyman-alpha profiles in this epoch are of particular interest since they hold information about the escape of ionizing radiation and the environment surrounding the source. Aims. We wish to understand the escape mechanisms of ionizing radiation in Lyα emitters during this time and the origin of a doubly peaked Lyman-alpha profile. We also wish to estimate the size of a potential ionized bubble. Methods. Using radiative transfer models, we fit the line profile of a bright Lyα emitter at z ∼ 6.9 using various gas geometries. The line modeling reveals significant radiation escape from this system. Results. The studied source shows significant escape (fesc(Lyα) ∼ 0.8, as predicted by the best fitting radiative transfer model) and appears to inhabit an ionized bubble of radius Rb ≈ 0.8−0.3+0.5 pMpc(tage/108)1/3. Radiative transfer modeling predicts the line to be completely redward of the systemic redshift. We suggest the line morphology is produced by inflows, by multiple components emitting Lyα, or by an absorbing component in the red wing. Conclusions. We propose that CDFS-1’s profile has two red peaks produced by winds within the system. Its high fesc(Lyα) and the low-velocity offset from the systemic redshift suggest that the source is an active ionizing agent. Future observations will reveal whether a peak is present blueward of the systemic redshift or if multiple components produce the profile.

A High-resolution Far-infrared Survey to Probe Black Hole–Galaxy Co-evolution

Far-infrared (FIR) surveys are critical to probing the co-evolution of black holes and galaxies, since of the order of half the light from accreting black holes and active star formation is emitted in the rest-frame IR over 0.5 ≲ z ≲ 10. For deep fields with areas of 1 deg2 or less, like the legacy surveys GOODS, COSMOS, and CANDELS, source crowding means that subarcsecond resolution is essential. In this paper, we show with a simulation of the FIR sky that observations made with a small telescope (2 m) at low angular resolution preferentially detect the brightest galaxies, and we demonstrate the scientific value of a space mission that would offer subarcsecond resolution. We envisage a facility that would provide high-resolution imaging and spectroscopy over the wavelength range 25–400 μm, and we present predictions for an extragalactic survey covering 0.5 deg2. Such a survey is expected to detect tens of thousands of star-forming galaxies and thousands of active galactic nuclei (AGNs), in multiple FIR lines (e.g., [C ii], [O i], and [C i]) and continuum. At the longest wavelengths (200–400 μm), it would probe beyond the Epoch of Reionization, up to z ∼ 7–8. A combination of spectral resolution, line sensitivity, and broad spectral coverage would allow us to learn about the physical conditions (temperature, density, and metallicity) characterizing the interstellar medium of galaxies over the past ∼12 billion years and to investigate galaxy–AGN co-evolution.

The impact of lossy data compression on the power spectrum of the high-redshift 21 cm signal with LOFAR

Current radio interferometers output multi-petabyte-scale volumes of data per year, making the storage, transfer, and processing of these data a sizeable challenge. This challenge is expected to grow with next-generation telescopes such as the Square Kilometre Array (SKA), which will produce a considerably larger data volume than current instruments. Lossy compression of interferometric data post-correlation can abate this challenge, but any drawbacks from the compression should be well understood in advance. Lossy data compression reduces the precision of data, introducing additional noise. Since high-redshift (e.g., cosmic dawn or epoch of reionization) 21 cm studies impose strict precision requirements, the impact of this effect on the 21 cm signal power spectrum statistic is investigated in a bid to rule out unwanted systematics. We applied dysco visibility compression, a technique for normalizing and quantizing specifically designed for radio interferometric data, to observed visibilities datasets from the LOFAR telescope as well as simulated ones. The power spectrum of these data was analyzed, and we establish the level of the compression noise in the power spectrum in comparison to the thermal noise. We also examined its coherency behavior by employing the cross-coherence metric. Finally, for optimal compression results, we compared the compression noise obtained from different compression settings to a nominal 21 cm signal power. From a single night of observation, we find that the noise introduced due to the compression is more than five orders of magnitude lower than the thermal noise level in the power spectrum. The noise does not affect calibration. Furthermore, the noise remains subdominant to the noise introduced by the nonlinear calibration algorithm used following random parameter initialization across different runs. The compression noise shows no correlation with the sky signal and has no measurable coherent component, therefore averaging down optimally with the integration of more data. The level of compression error in the power spectrum ultimately depends on the compression settings. dysco visibility compression is found to be an insignificant concern for 21 cm power spectrum studies. Hence, data volumes can be safely reduced by factors of $ 4$ with insignificant bias to the final power spectrum. Data from SKA-Low will likely be compressible by the same factor as data from LOFAR owing to the similarities of the two instruments. The same technique can be used to compress data from other telescopes, but a small adjustment of the compression parameters might be required.

Ionising properties of galaxies in JADES for a stellar mass complete sample: resolving the cosmic ionising photon budget crisis at the Epoch of Reionisation

Abstract We use NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) to study the ionising properties of a sample of 14652 galaxies at 3 ≤ zphot ≤ 9, 90% complete in stellar mass down to log(M⋆/[M⊙]) ≈ 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 ionising photon production efficiency (ξion) with redshift and UV magnitude than previously reported. Interestingly, we observe two distinct populations in ξion, distinguished by their burstiness (given by SFR10/SFR100). Both populations show the same evolution with z and MUV, but have a different ξion normalisation. We convolve the more representative log (ξion(z, MUV)) relations (accounting for ∼97% of the sample), with luminosity functions from literature, to place constraints on the cosmic ionising photon budget. By combining our results, we find that one of our models can match the observational constraints from the Lyα forest at z ≲ 6. We conclude that galaxies with MUV between −16 and −20, adopting a reasonable escape fraction, can produce enough ionising photons to ionise the Universe, without exceeding the required ionising photon budget.

The importance of stochasticity in determining galaxy emissivities and UV LFs during cosmic dawn and reionization

The stochastic nature of star formation and photon propagation in high-redshift galaxies can result in sizable galaxy-to-galaxy scatter in their properties. Ignoring this scatter by assuming mean quantities can bias estimates of their emissivity and corresponding observables. We constructed a flexible, semi-empirical model, sampling scatter around the following mean relations: (i) the conditional halo mass function (CHMF); (ii) the stellar-to-halo mass relation (SHMR); (iii) the galaxy star formation main sequence (SFMS); (iv) the fundamental metallicity relation (FMR); (v) the conditional intrinsic luminosity; and (vi) the photon escape fraction. In our fiducial model, ignoring scatter in these galaxy properties overestimates the duration of the Epoch of Reionization (EoR), delaying its completion by $ z 1--2. We quantified the relative importance of each of the above sources of scatter in determining the ionizing, soft-band X-ray, and Lyman Werner (LW) emissivities as a function of scale and redshift. We find that scatter around the SFMS is important for all bands, especially at the highest redshifts where the emissivity is dominated by the faintest, most "bursty" galaxies. Ignoring this scatter would underestimate the mean emissivity and its standard deviation computed over 5 cMpc regions by factors of up to sim 2--10 at $5 z 15$. The scatter around the X-ray luminosity to star formation rate and metallicity relation is important for determining X-ray emissivity, accounting for roughly half of its mean and standard deviation. The importance of scatter in the ionizing escape fraction depends on its functional form, while scatter around the SHMR contributes at the level of sim 10--20&lt;!PCT!&gt;. Other sources of scatter have a negligible contribution to the emissivities. Although scatter does flatten the UV luminosity functions, shifting the bright end by 1--2 magnitudes, the level of scatter in our fiducial model is insufficient to fully explain recent estimates from JWST photometry (consistent with previous studies). We conclude that models of the EoR should account for the burstiness of star formation, while models for the cosmic 21cm signal should additionally account for scatter in intrinsic X-ray production.

Power spectrum multipoles and clustering wedges during the Epoch of Reionization

Abstract 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 ∼ 7 − 9 corresponding to a line-of-sight scale of ∼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 k-space is highly non-uniform due to the baseline distribution, i.e. the distribution of antenna pairs sampling different transverse k⊥ scales. Measurements in clustering wedges partition the cylindrical k-space into different radial k∥ scales, and can be used for isolating parts of 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 ∼120 hrs 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 ∼3 improvement on the marginalised 1D parameter constraints.

A SPectroscopic Survey of Biased Halos In the Reionization Era (ASPIRE): JWST Supports Earlier Reionization around [O iii] Emitters

Understanding when and how reionization happened is crucial for studying the early structure formation and the properties of the first galaxies in the Universe. At z > 5.5, the observed intergalactic medium (IGM) optical depth shows a significant scatter, indicating an inhomogeneous reionization process. However, the nature of the inhomogeneous reionization remains debated. A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE) is a JWST Cycle 1 program that has spectroscopically identified >400 [O iii] emitters in 25 quasar fields at z > 6.5. Combined with deep ground-based optical spectroscopy of ASPIRE quasars, the ASPIRE program provides the current largest sample for IGM-galaxy connection studies during cosmic reionization. We present the first results of IGM effective optical depth measurements around [O iii] emitters using 14 ASPIRE quasar fields. We find the IGM transmission is tightly related to reionization era galaxies to the extent that a significant excess of Lyα transmission exists around [O iii] emitters. We measure the stacked IGM effective optical depth of IGM patches associated with [O iii] emitters and find they reach the same IGM effective optical depth at least d z ∼ 0.1 ahead of those IGM patches where no [O iii] emitters are detected, supporting earlier reionization around [O iii] emitters. Our results indicate an enhancement in IGM Lyα transmission around [O iii] emitters at scales beyond 25 h −1 cMpc, consistent with the predicted topology of reionization from fluctuating UV background models.