Reionization History Research Articles

Can Population III stars be major origins of both merging binary black holes and extremely metal poor stars?

Abstract Population (Pop) III stars, first stars, or metal-free stars are made of primordial gas. We have examined if they can be dominant origins of merging binary black holes (BHs) and extremely metal-poor (EMP) stars. The abundance pattern of EMP stars is helpful to trace back the properties of Pop III stars. We have confirmed previous arguments that the observed BH merger rate needs Pop III star formation efficiency 10 times larger than theoretically predicted values, while the cosmic reionization history still permits such a high Pop III star formation efficiency. On the other hand, we have newly found that the elemental abundance pattern of EMP stars only allows the Pop III initial mass function with the minimum mass of ∼15–27 M$_{\odot}$. In other words, the minimum mass must not deviate largely from the critical mass below and above which Pop III stars leave behind neutron stars and BHs, respectively. Pop III stars may still be a dominant origin of merging binary BHs but our study has reduced the allowed parameter space under the hypothesis that EMP stars are formed from primordial gas mixed with Pop III supernova ejecta.

Streaming velocity effects on the post-reionization 21-cm baryon acoustic oscillation signal

ABSTRACTThe relative velocity between baryons and dark matter in the early Universe can suppress the formation of small-scale baryonic structure and leave an imprint on the baryon acoustic oscillation (BAO) scale at low redshifts after reionization. This ‘streaming velocity’ affects the post-reionization gas distribution by directly reducing the abundance of pre-existing mini-haloes ($\lesssim 10^7 {\rm M}_{\bigodot }$) that could be destroyed by reionization and indirectly modulating reionization history via photoionization within these mini-haloes. In this work, we investigate the effect of streaming velocity on the BAO feature in H i 21 cm intensity mapping after reionization, with a focus on redshifts 3.5 ≲ z ≲ 5.5. We build a spatially modulated halo model that includes the dependence of the filtering mass on the local reionization redshift and thermal history of the intergalactic gas. In our fiducial model, we find isotropic streaming velocity bias coefficients bv ranging from −0.0043 at z = 3.5 to −0.0273 at z = 5.5, which indicates that the BAO scale is stretched (i.e. the peaks shift to lower k). In particular, streaming velocity shifts the transverse BAO scale between 0.121 per cent (z = 3.5) and 0.35 per cent (z = 5.5) and shifts the radial BAO scale between 0.167 per cent (z = 3.5) and 0.505 per cent (z = 5.5). These shifts exceed the projected error bars from the more ambitious proposed hemispherical-scale surveys in H i (0.13 per cent at 1σ per Δz = 0.5 bin).

AMBER: A Semi-numerical Abundance Matching Box for the Epoch of Reionization

Abstract The Abundance Matching Box for the Epoch of Reionization (AMBER) is a semi-numerical code for modeling the cosmic dawn. The new algorithm is not based on the excursion set formalism for reionization, but takes the novel approach of calculating the reionization-redshift field z re ( x ) assuming that hydrogen gas encountering higher radiation intensity are photoionized earlier. Redshift values are assigned while matching the abundance of ionized mass according to a given mass-weighted ionization fraction x ¯ i ( z ) . The code has the unique advantage of allowing users to directly specify the reionization history through the redshift midpoint z mid, duration Δz, and asymmetry A z input parameters. The reionization process is further controlled through the minimum halo mass M min for galaxy formation and the radiation mean free path l mfp for radiative transfer. We implement improved methods for constructing density, velocity, halo, and radiation fields, which are essential components for modeling reionization observables. We compare AMBER with two other semi-numerical methods and find that our code more accurately reproduces the results from radiation-hydrodynamic simulations. The parallelized code is over four orders of magnitude faster than radiative transfer simulations and will efficiently enable large-volume models, full-sky mock observations, and parameter-space studies. AMBER will be made publicly available to facilitate and transform studies of the Epoch of Reionization.

Thethesanproject: properties of the intergalactic medium and its connection to reionization-era galaxies

ABSTRACTThe high-redshift intergalactic medium (IGM) and the primeval galaxy population are rapidly becoming the new frontier of extragalactic astronomy. We investigate the IGM properties and their connection to galaxies at z ≥ 5.5 under different assumptions for the ionizing photon escape and the nature of dark matter, employing our novel thesan radiation-hydrodynamical simulation suite, designed to provide a comprehensive picture of the emergence of galaxies in a full reionization context. Our simulations have realistic ‘late’ reionization histories, match available constraints on global IGM properties, and reproduce the recently observed rapid evolution of the mean free path of ionizing photons. We additionally examine high-z Lyman-α transmission. The optical depth evolution is consistent with data, and its distribution suggests an even-later reionization than simulated, although with a strong sensitivity to the source model. We show that the effects of these two unknowns can be disentangled by characterizing the spectral shape and separation of Lyman-α transmission regions, opening up the possibility to observationally constrain both. For the first time in simulations, thesan reproduces the modulation of the Lyman-α flux as a function of galaxy distance, demonstrating the power of coupling a realistic galaxy formation model with proper radiation hydrodynamics. We find this feature to be extremely sensitive on the timing of reionization, while being relatively insensitive to the source model. Overall, thesan produces a realistic IGM and galaxy population, providing a robust framework for future analysis of the high-z Universe.

Exploring the High-redshift PBH-ΛCDM Universe: Early Black Hole Seeding, the First Stars and Cosmic Radiation Backgrounds

Abstract We explore the observational implications of a model in which primordial black holes (PBHs) with a broad birth mass function ranging in mass from a fraction of a solar mass to ∼106 M ⊙, consistent with current observational limits, constitute the dark matter (DM) component in the universe. The formation and evolution of dark matter and baryonic matter in this PBH-Λ cold dark matter (ΛCDM) universe are presented. In this picture, PBH-DM mini-halos collapse earlier than in standard ΛCDM, baryons cool to form stars at z ∼ 15–20, and growing PBHs at these early epochs start to accrete through Bondi capture. The volume emissivity of these sources peaks at z ∼ 20 and rapidly fades at lower redshifts. As a consequence, PBH DM could also provide a channel to make early black hole seeds and naturally account for the origin of an underlying DM halo–host galaxy and central black hole connection that manifests as the M bh–σ correlation. To estimate the luminosity function and contribution to integrated emission power spectrum from these high-redshift PBH-DM halos, we develop a halo occupation distribution model. In addition to tracing the star formation and reionization history, it permits us to evaluate the cosmic infrared and X-ray backgrounds. We find that accretion onto PBHs/active galactic nuclei successfully accounts for the detected backgrounds and their cross-correlation, with the inclusion of an additional IR stellar emission component. Detection of the deep IR source count distribution by the James Webb Space Telescope could reveal the existence of this population of high-redshift star-forming and accreting PBH DM.

Epoch of reionization parameter estimation with the 21-cm bispectrum

ABSTRACT We present the first application of the isosceles bispectrum to MCMC parameter inference from the cosmic 21-cm signal. We extend the MCMC sampler 21CMMC to use the fast bispectrum code, BiFFT, when computing the likelihood. We create mock 1000-h observations with SKA1-low, using pyObs21 to account for uv-sampling and thermal noise. Assuming the spin temperature is much higher than that of the cosmic microwave background, we consider two different reionization histories for our mock observations: fiducial and late-reionization. For both models we find that bias on the inferred parameter means and 1σ credible intervals can be substantially reduced by using the isosceles bispectrum (calculated for a wide range of scales and triangle shapes) together with the power spectrum (as opposed to just using one of the statistics). We find that making the simplifying assumption of a Gaussian likelihood with a diagonal covariance matrix does not notably bias parameter constraints for the three-parameter reionization model and basic instrumental effects considered here. This is true even if we use extreme (unlikely) initial conditions which would be expected to amplify biases. We also find that using the cosmic variance error calculated with Monte Carlo simulations using the fiducial model parameters while assuming the late-reionization model for the simulated data also does not strongly bias the inference. This implies we may be able to sparsely sample and interpolate the cosmic variance error over the parameter space, substantially reducing computational costs. All codes used in this work are publicly available.

Probing ultra-light axion dark matter from 21 cm tomography using Convolutional Neural Networks

We present forecasts on the detectability of Ultra-light axion-like particles (ULAP) from future 21 cm radio observations around the epoch of reionization (EoR). We show that the axion as the dominant dark matter component has a significant impact on the reionization history due to the suppression of small scale density perturbations in the early universe. This behavior depends strongly on the mass of the axion particle. Using numerical simulations of the brightness temperature field of neutral hydrogen over a large redshift range, we construct a suite of training data. This data is used to train a convolutional neural network that can build a connection between the spatial structures of the brightness temperature field and the input axion mass directly. We construct mock observations of the future Square Kilometer Array survey, SKA1-Low, and find that even in the presence of realistic noise and resolution constraints, the network is still able to predict the input axion mass. We find that the axion mass can be recovered over a wide mass range with a precision of approximately 20%, and as the whole DM contribution, the axion can be detected using SKA1-Low at 68% if the axion mass is M X < 1.86 × 10-20 eV although this can decrease to M X < 5.25 × 10-21 eV if we relax our assumptions on the astrophysical modeling by treating those astrophysical parameters as nuisance parameters.

Dark twilight joined with the light of dawn to unveil the reionization history

Improved measurement of the Cosmic Microwave Background polarization from Planck allows a detailed study of reionization beyond the average optical depth. The lower value of the optical depth disfavours an early onset and an early completion of reionization in favour of a redsfhit range where different astrophysical probes provide sensible information on the sources of reionization and the status of the intergalactic medium. In this work we extend our previous study in which we constrained reionization by combining three different probes - CMB, UV luminosity density and neutral hydrogen fraction data - in both treatment and data: we first allow variation in the UV source term varying the product of the efficiency of conversion of UV luminosity into ionizing photons and the escape fraction together with the reionization and cosmological parameters, and then we investigate the impact of a less conservative cut for the UV luminosity function. We find that the estimate for the efficiency is consistent within 95% C.L. with the fixed value we considered in our previous results and is mostly constrained by the QHII data. We find that allowing the efficiency to vary does not affect significantly our results for the average optical depth for monotonic reionization histories, recovering $\tau=0.0519_{-0.0008}^{+0.0010}$ at 68% CL , consistent with our previous studies. Using a less conservative cut for the UV luminosity function, we find $\tau=0.0541_{-0.0016}^{+0.0013}$ at 68% CL, due to the faint end of the luminosity function in the data we use, that also prefers a larger contribution from higher redshifts.

Introducing the thesan project: radiation-magnetohydrodynamic simulations of the epoch of reionization

ABSTRACT We introduce the thesan project, a suite of large volume ($L_\mathrm{box} = 95.5 \, \mathrm{cMpc}$) radiation-magnetohydrodynamic simulations that simultaneously model the large-scale statistical properties of the intergalactic medium during reionization and the resolved characteristics of the galaxies responsible for it. The flagship simulation has dark matter and baryonic mass resolutions of $3.1 \times 10^6\, {\rm M_\odot }$ and $5.8 \times 10^5\, {\rm M_\odot }$, respectively. The gravitational forces are softened on scales of 2.2 ckpc with the smallest cell sizes reaching 10 pc at z = 5.5, enabling predictions down to the atomic cooling limit. The simulations use an efficient radiation hydrodynamics solver (arepo-rt) that precisely captures the interaction between ionizing photons and gas, coupled to well-tested galaxy formation (IllustrisTNG) and dust models to accurately predict the properties of galaxies. Through a complementary set of medium resolution simulations we investigate the changes to reionization introduced by different assumptions for ionizing escape fractions, varying dark matter models, and numerical convergence. The fiducial simulation and model variations are calibrated to produce realistic reionization histories that match the observed evolution of the global neutral hydrogen fraction and electron scattering optical depth to reionization. They also match a wealth of high-redshift observationally inferred data, including the stellar-to-halo-mass relation, galaxy stellar mass function, star formation rate density, and the mass–metallicity relation, despite the galaxy formation model being mainly calibrated at z = 0. We demonstrate that different reionization models give rise to varied bubble size distributions that imprint unique signatures on the 21 cm emission, especially on the slope of the power spectrum at large spatial scales, enabling current and upcoming 21 cm experiments to accurately characterize the sources that dominate the ionizing photon budget.

Gaussian Process Reconstruction of Reionization History

Abstract We reconstruct the history of reionization using Gaussian process regression. Using the UV luminosity data compilation from Hubble Frontiers Fields we reconstruct the redshift evolution of UV luminosity density and thereby the evolution of the source term in the ionization equation. This model-independent reconstruction rules out single power-law evolution of the luminosity density but supports the logarithmic double power-law parameterization. We obtain reionization history by integrating ionization equations with the reconstructed source term. Using the optical depth constraint from Planck cosmic microwave background observation, measurement of UV luminosity function integrated until truncation magnitude of −17 and −15, and derived ionization fraction from high redshift quasar, galaxies, and gamma-ray burst observations, we constrain the history of reionization. In the conservative case we find the constraint on the optical depth as τ = 0.052 ± 0.001 ± 0.002 at 68% and 95% confidence intervals. We find the redshift duration between 10% and 90% ionization to be 2.05 − 0.21 − 0.30 + 0.11 + 0.37 . Longer duration of reionization is supported if UV luminosity density data with truncation magnitude of −15 is used in the joint analysis. Our results point out that even in a conservative reconstruction, a combination of cosmological and astrophysical observations can provide stringent constraints on the epoch of reionization.

Optimal 1D Ly α forest power spectrum estimation – II. KODIAQ, SQUAD, and XQ-100

ABSTRACT We measure the 1D Ly α power spectrum P1D from Keck Observatory Database of Ionized Absorption toward Quasars (KODIAQ), The Spectral Quasar Absorption Database (SQUAD), and XQ-100 quasars using the optimal quadratic estimator. We combine KODIAQ and SQUAD at the spectrum level, but perform a separate XQ-100 estimation to control its large resolution corrections in check. Our final analysis measures P1D at scales k &amp;lt; 0.1 s km−1 between redshifts $z$ = 2.0–4.6 using 538 quasars. This sample provides the largest number of high-resolution, high-S/N observations; and combined with the power of optimal estimator it provides exceptional precision at small scales. These small-scale modes (k ≳ 0.02 s km−1), unavailable in Sloan Digital Sky Survey and Dark Energy Spectroscopic Instrument analyses, are sensitive to the thermal state and reionization history of the intergalactic medium, as well as the nature of dark matter. As an example, a simple Fisher forecast analysis estimates that our results can improve small-scale cut-off sensitivity by more than a factor of 2.

Semi-analytic forecasts for JWST – V. AGN luminosity functions and helium reionization at z = 2–7

ABSTRACT Active galactic nuclei (AGN) forming in the early universe are thought to be the primary source of hard ionizing photons contributing to the reionization of intergalactic helium. However, the number density and spectral properties of high-redshift AGN remain largely unconstrained. In this work, we make use of physically informed models calibrated with a wide variety of available observations to provide estimates for the role of AGN throughout the Epoch of Reionization. We present AGN luminosity functions in various bands between z = 2 and 7 predicted by the well-established Santa Cruz semi-analytic model, which includes modelling of black hole accretion and AGN feedback. We then combine the predicted AGN populations with a physical spectral model for self-consistent estimates of ionizing photon production rates, which depend on the mass and accretion rate of the accreting supermassive black hole. We then couple the predicted comoving ionizing emissivity with an analytic model to compute the subsequent reionization history of intergalactic helium and hydrogen. This work demonstrates the potential of coupling physically motivated analytic or semi-analytic techniques to capture multiscale physical processes across a vast range of scales (here, from AGN accretion discs to cosmological scales). Our physical model predicts an intrinsic ionizing photon budget well above many of the estimates in the literature, meaning that helium reionization can comfortably be accomplished even with a relatively low escape fraction. We also make predictions for the AGN populations that are expected to be detected in future James Webb Space Telescope surveys.

Reionization effective likelihood fromPlanck2018 data

We release RELIKE (Reionization Effective Likelihood), a fast and accurate effective likelihood code based on the latest Planck 2018 data that allows one constrain any model for reionization between $6 < z < 30$ using five constraints from the CMB reionization principal components (PC). We tested the code on two example models which showed excellent agreement with sampling the exact Planck likelihoods using either a simple Gaussian PC likelihood or its full kernel density estimate. This code enables a fast and consistent means for combining Planck constraints with other reionization data sets, such as kinetic Sunyaev-Zeldovich effects, line-intensity mapping, luminosity function, star formation history, quasar spectra, etc, where the redshift dependence of the ionization history is important. Since the PC technique tests any reionization history in the given range, we also derive model-independent constraints for the total Thomson optical depth $\tau_{\rm PC} = 0.0619^{+0.0056}_{-0.0068}$ and its $15\le z \le 30$ high redshift component $\tau_{\rm PC}(15, 30) < 0.020 $ (95\% C.L.). The upper limits on the high-redshift optical depth is a factor of $\sim3$ larger than those reported in the Planck 2018 cosmological parameter paper using the FlexKnot method and we validate our results with a direct analysis of a two-step model which permits this small high-$z$ component.

Using the sample variance of 21 cm maps as a tracer of the ionisation topology

Intensity mapping of the 21 cm signal of neutral hydrogen will yield exciting insights into the Epoch of Reionisation and the nature of the first galaxies. However, the large amount of data that will be generated by the next generation of radio telescopes, such as the Square Kilometre Array, as well as the numerous observational obstacles to overcome, require analysis techniques tuned to extract the reionisation history and morphology. In this context, we introduce a one-point statistic, which we refer to as the local variance,σloc, that describes the distribution of the mean differential 21 cm brightness temperatures measured in two-dimensional maps along the frequency direction of a light cone. The local variance takes advantage of what is usually considered an observational bias, the sample variance. We find the redshift-evolution of the local variance to not only probe the reionisation history of the observed patches of the sky, but also trace the ionisation morphology. This estimator provides a promising tool to constrain the midpoint of reionisation as well as gain insight into the ionising properties of early galaxies.

C ii and H i 21-cm line intensity mapping from the EoR: impact of the light-cone effect on auto and cross-power spectra

ABSTRACT C ii line intensity mapping (LIM) is a potential technique to probe the early galaxies from the Epoch of Reionization (EoR). Several experiments e.g. CONCERTO, TIME, CCAT-p are underway to map the C ii LIM signal fluctuations from the EoR, enabling us to estimate the C ii power-spectrum and C ii × 21-cm cross-power spectrum. The observed LIM signal will have its time evolution embedded in it along the line of sight due to the finite traveltime of the signal from its origin to the observer. We have investigated this so-called light-cone effect on the observed statistics of our seminumerically simulated C ii signal from the EoR. Using a suit of simulated C ii and neutral hydrogen 21-cm maps and corresponding light-cone boxes, we have shown that the light-cone effect can impact the C ii power spectrum by more than 15 per cent at large scales ($k\sim 0.1\, \text{Mpc}^{-1}$, at $z$ = 6.8). We have also observed that the impact of light-cone effect on the C ii power spectrum drops with decreasing redshift within the redshift range considered here (7.2 ≲ $z$ ≲ 6). The C ii × 21-cm cross-power spectrum is also affected by light cone, and in our models where reionization ends before $z$ = 6, we find that the maximum impact on cross-power can reach up to 20 per cent. At $z$ = 6.4, we find comparatively pronounced variation in the light-cone effect with reionization history on the cross-power. Faster reionization histories have a more drastic light-cone effect on cross-power. We conclude that we need to incorporate the light cone in order to properly model the signal, constrain the EoR-related astrophysical parameters and reionization history using the C ii × 21-cm cross-power spectrum.

Future Constraints on the Reionization History and the Ionizing Sources from Gamma-Ray Burst Afterglows

Abstract We forecast the reionization history constraints, inferred from Lyα damping wing absorption features, for a future sample of ∼20 z ≥ 6 gamma-ray burst (GRB) afterglows. We describe each afterglow spectrum by a three-parameter model. First, L characterizes the size of the ionized region (the “bubble size”) around a GRB host halo. Second, 〈x H i 〉 is the volume-averaged neutral fraction outside of the ionized bubble around the GRB, which is approximated as spatially uniform. Finally, N H i denotes the column density of a local damped Lyα absorber (DLA) associated with the GRB host galaxy. The size distribution of ionized regions is extracted from a numerical simulation of reionization and evolves strongly across the epoch of reionization (EoR). The model DLA column densities follow the empirical distribution determined from current GRB afterglow spectra. We use a Fisher matrix formalism to forecast the 〈x H i (z)〉 constraints that can be obtained from follow-up spectroscopy of afterglows with S/N = 20 per R = 3000 resolution element at the continuum. We find that the neutral fraction may be determined to better than 10%–15% (1σ) accuracy from this data across multiple independent redshift bins at z ∼ 6–10, spanning much of the EoR, although the precision degrades somewhat near the end of reionization. A more futuristic survey with 80 GRB afterglows at z ≥ 6 can improve the precision here by a factor of 2 and extend measurements out to z ∼ 14. We further discuss how these constraints may be combined with estimates of the escape fraction of ionizing photons derived from the DLA column density distribution toward GRBs extracted at slightly lower redshift, z ∼ 5. This combination will help in testing whether we have an accurate census of the sources that reionized the universe.

Introducing SPHINX-MHD: the impact of primordial magnetic fields on the first galaxies, reionization, and the global 21-cm signal

ABSTRACT We present the first results from SPHINX-MHD, a suite of cosmological radiation-magnetohydrodynamics simulations designed to study the impact of primordial magnetic fields (PMFs) on galaxy formation and the evolution of the intergalactic medium (IGM) during the epoch of reionization. The simulations are among the first to employ multifrequency, on-the-fly radiation transfer and constrained transport ideal MHD in a cosmological context to simultaneously model the inhomogeneous process of reionization as well as the growth of primordial magnetic fields. We run a series of $(5\, \text{cMpc})^3$ cosmological volumes, varying both the strength of the seed magnetic field and its spectral index. We find that PMFs with a spectral index (nB) and a comoving amplitude (B0) that have $\scriptstyle{n_B \gt -0.562\log _{10}\left(\frac{B_0}{1{\rm n}G}\right) - 3.35}$ produce electron optical depths (τe) that are inconsistent with CMB constraints due to the unrealistically early collapse of low-mass dwarf galaxies. For nB ≥ −2.9, our constraints are considerably tighter than the ∼nG constraints from Planck. PMFs that do not satisfy our constraints have little impact on the reionization history or the shape of the UV luminosity function. Likewise, detecting changes in the Ly α forest due to PMFs will be challenging because photoionization and photoheating efficiently smooth the density field. However, we find that the first absorption feature in the global 21-cm signal is a particularly sensitive indicator of the properties of the PMFs, even for those that satisfy our τe constraint. Furthermore, strong PMFs can marginally increase the escape of LyC photons by up to 25 per cent and shrink the effective radii of galaxies by $\sim 44{{\ \rm per\ cent}}$ which could increase the completeness fraction of galaxy surveys. Finally, our simulations show that surveys with a magnitude limit of ${\rm \mathit{ M}_{UV,1500\,\mathring{\rm A}}=-13}$ can probe the sources that provide the majority of photons for reionization out to z = 12.

Probing reionization and early cosmic enrichment with the Mg iiforest

ABSTRACTBecause the same massive stars that reionized the intergalactic medium (IGM) inevitably exploded as supernovae that polluted the Universe with metals, the history of cosmic reionization and enrichment is intimately intertwined. While the overly sensitive Ly α transition completely saturates in a neutral IGM, strong low-ionization metal lines like the $\rm{Mg\, \small {II}}$ λ2796, λ2804 doublet will give rise to a detectable ‘metal-line forest’ if the metals produced during reionization ($Z\sim 10^{-3}\, \mathrm{Z}_{\odot }$) permeate the neutral IGM. We simulate the $\rm{Mg\,\small {II}}$ forest for the first time by combining a large hydrodynamical simulation with a seminumerical reionization topology, assuming a simple enrichment model where the IGM is uniformly suffused with metals. In contrast to the traditional approach of identifying discrete absorbers, we treat the absorption as a continuous random field and measure its two-point correlation function, leveraging techniques from precision cosmology. We show that a realistic mock data set of 10 James Webb Space Telescope spectra can simultaneously determine the Mg abundance, $[{\rm Mg}/{\rm H}]$, with a 1σ precision of 0.02 dex and measure the global neutral fraction $\langle x_{\rm{H\,\small {I}}}\rangle$ to 5 per cent for a Universe with $\langle x_{\rm{H\,\small {I}}}\rangle = 0.74$ and $[{\rm Mg}/ {\rm H}] = -3.7$. Alternatively, if the IGM is pristine, a null detection of the $\rm{Mg\,\small {II}}$ forest would set a stringent upper limit on the IGM metallicity of $[{\rm Mg}/ {\rm H}] \lt -4.4$ at 95 per cent credibility, assuming $\langle x_{\rm{H\,\small {I}}}\rangle \gt 0.5$ from another probe. Concentrations of metals in the circumgalactic environs of galaxies can significantly contaminate the IGM signal, but we demonstrate how these discrete absorbers can be easily identified and masked such that their impact on the correlation function is negligible. The $\rm{Mg\,\small {II}}$ forest thus has tremendous potential to precisely constrain the reionization and enrichment history of the Universe.

Population III star explosions and Planck 2018 data

We investigate the effect of the population III (Pop III) stars supernova explosion (SN) on the high redshifts reionization history using the latest Planck data. It is predicted that massive Pop III stars $(130\text{ }\text{ }{M}_{\ensuremath{\bigodot}}\ensuremath{\le}M\ensuremath{\le}270\text{ }\text{ }{M}_{\ensuremath{\bigodot}})$ explode energetically at the end of their stellar life as pair-instability supernovae (PISNe). In the explosion, supernova remnants grow as hot ionized bubbles and enhance the ionization fraction in the early stage of the reionization history. This enhancement affects the optical depth of the cosmic microwave background (CMB) and generates the additional anisotropy of the CMB polarization on large scales. Therefore, analyzing the Planck polarization data allows us to examine the Pop III star SNe and the abundance of their progenitors, massive Pop III stars. In order to model the supernova(SN) contribution to reionization, we introduce a new parameter $\ensuremath{\zeta}$, which relates to the abundance of the SNe to the collapse fraction of the Universe. Using the Markov chain Monte Carlo method with the latest Planck polarization data, we obtain the constraint on our model parameter, $\ensuremath{\zeta}$. Our constraint tells us that observed CMB polarization is consistent with the abundance of PISNe predicted from the star formation rate and initial mass function of Pop III stars in recent cosmological simulations. We also suggest that combining further observations on the late reionization history, such as high redshift quasi-stellar object (QSO) observations, can provide tighter constraints and important information on the nature of Pop III stars.

Cosmic Reionization May Still Have Started Early and Ended Late: Confronting Early Onset with Cosmic Microwave Background Anisotropy and 21 cm Global Signals

Abstract The global history of reionization was shaped by the relative amounts of starlight released by three halo mass groups: the first two groups are atomic-cooling halos (ACHs) with virial temperatures T vir &gt; 104 K, either (1) massive enough to form stars even after reionization (high-mass ACHs, ≳ 109 M ⊙) or (2) less massive (low-mass ACHs), subject to star formation suppression when overtaken by reionization, and the third group comprises (3) H2-cooling mini-halos (MHs) with T vir &lt; 104 K, whose star formation is predominantly suppressed by the H2-dissociating Lyman–Werner background. Our previous work showed that including MHs caused two-stage reionization—early rise to x ≲ 0.1, driven by MHs, followed by a rapid rise, late, to x ∼ 1, driven by ACHs—with a signature in cosmic microwave background (CMB) polarization anisotropy predicted to be detectable by the Planck satellite. Motivated by this prediction, we model global reionization semi-analytically for comparison with Planck CMB data and the Experiment to Detect the Global Epoch of Reionization (EDGES) global 21 cm absorption feature, for models with: (1) ACHs, no feedback; (2) ACHs, self-regulated; and (3) ACHs and MHs, self-regulated. Model (3) agrees well with Planck E-mode polarization data, even with a substantial tail of high-redshift ionization, beyond the limit proposed by the Planck Collaboration. No model reproduces the EDGES feature. For model (3), across the EDGES trough, an order of magnitude too shallow, and absorption starts at higher z but is spectrally featureless. Early onset reionization by Population III stars in MHs is compatible with current constraints, but only if the EDGES interpretation is discounted, or else other processes we did not include account for it.