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Recently, models of the quasar luminosity function (QLF) rooted on large observational compilations have been produced that, unlike their predecessors, feature a smooth evolution with time. This bypasses the need to assume an ionizing emissivity evolution when simulating helium reionization with observations-based QLF, thus yielding more robust constraints. We combine one such QLF with a cosmological hydrodynamical simulation and 3D multifrequency radiative transfer. The simulated reionization history is consistently delayed in comparison to most other models in the literature. The predicted intergalactic medium temperature is larger than the observed one at |$z \lesssim 3$|⁠. Through forward modelling of the He  ii Lyman  |$\alpha$| forest, we show that our model produces an extended helium reionization and successfully matches the bulk of the observed effective optical depth distribution, although it overionizes the Universe at |$z\lesssim 2.8$| as the effect of small-scale Lyman Limit Systems not being resolved. We thoroughly characterize transmission regions and dark gaps in He  ii Lyman  |$\alpha$| forest sightlines. We quantify their sensitivity to the helium reionization, opening a new avenue for further observational studies of this epoch. Finally, we explore the implications for helium reionization of the large number of active galactic nuclei revealed at |$z\gtrsim 5$| by JWST. We find that such modifications do not affect any observable at |$z\le 4$|⁠ , except in our most extreme model, indicating that the observed abundance of high- z AGNs does not bear consequences for helium reionization. [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]

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

In recent years, a Gaussian process regression (GPR)-based framework has been developed for foreground mitigation from data collected by the LOw-Frequency ARray (LOFAR), to measure the 21-cm signal power spectrum from the Epoch of Reionization (EoR) and cosmic dawn. However, it has been noted that through this method there can be a significant amount of signal loss if the EoR signal covariance is misestimated. To obtain better covariance models, we propose to use a kernel trained on the grizzly simulations using a Variational Auto-Encoder (VAE)-based algorithm. In this work, we explore the abilities of this machine learning-based kernel (VAE kernel) used with GPR, by testing it on mock signals from a variety of simulations, exploring noise levels corresponding to ≈10 nights (≈141 h) and ≈100 nights (≈1410 h) of observations with LOFAR. Our work suggests the possibility of successful extraction of the 21-cm signal within 2σ uncertainty in most cases using the VAE kernel, with better recovery of both shape and power than with previously used covariance models. We also explore the role of the excess noise component identified in past applications of GPR and additionally analyse the possibility of redshift dependence on the performance of the VAE kernel. The latter allows us to prepare for future LOFAR observations at a range of redshifts, as well as compare with results from other telescopes. [ABSTRACT FROM AUTHOR]

To self-consistently model galactic properties, reionization of the intergalactic medium, and the associated 21-cm signal, we have developed the algorithm polar by integrating the one-dimensional radiative transfer code grizzly with the semi-analytical galaxy formation code L-Galaxies 2020. Our proof-of-concept results are consistent with observations of the star formation rate history, UV luminosity function, and the CMB Thomson scattering optical depth. We then investigate how different galaxy formation models affect UV luminosity functions and 21-cm power spectra, and find that while the former are most sensitive to the parameters describing the merger of haloes, the latter have a stronger dependence on the supernovae feedback parameters, and both are affected by the escape fraction model. [ABSTRACT FROM AUTHOR]

In this work, we investigate the dependence of the escape fraction of ionizing photons, f esc, on various galaxy and host halo properties during the epoch of reionization. We post-process the TNG50 magnetohydrodynamical simulation from the IllustrisTNG project using the three-dimensional multifrequency radiative transfer code CRASH. Our work covers the stellar mass range of 106 ≲ M ⋆/M⊙ ≲ 108 at redshifts 6 < z < 10. Adopting an unresolved, cloud-scale escape fraction parameter of unity, the average halo escape fraction f esc increases with mass from ∼0.3 at M ⋆ = 106 M⊙ to ∼0.6 at M ⋆ = 107.5 M⊙, after which we find hints of a turnover and decreasing escape fractions for even more massive galaxies. However, we demonstrate a strong and non-linear dependence of f esc on the adopted subgrid escape fraction, resulting in uncertainties for the absolute value of the escape fraction. In addition, f esc has significant scatter at fixed mass, driven by diversity in the ionizing photon rate together with a complex relationship between (stellar) source positions and the underling density distribution. The global emissivity is consistent with observations for reasonable cloud-scale absorption values, and haloes with a stellar mass ≲107.5 M⊙ contribute the majority of escaping ionizing photons at all redshifts. Incorporating dust reduces f esc by a few per cent at M ⋆ ≲ 106.5 M⊙, and up to 10  per cent for larger haloes. Our multifrequency approach shows that f esc depends on photon energy, and is reduced substantially at E > 54.4 eV versus lower energies. This suggests that the impact of high-energy photons from binary stars is reduced when accounting for an energy-dependent escape fraction. [ABSTRACT FROM AUTHOR]

Overdense, metal-rich regions, shielded from stellar radiation might remain neutral throughout reionization and produce metal as well as 21 cm absorption lines. Simultaneous absorption from metals and 21 cm can complement each other as probes of underlying gas properties. We use Aurora, a suite of high-resolution radiation-hydrodynamical simulations of galaxy formation, to investigate the occurrence of such 'aligned' absorbers. We calculate absorption spectra for 21 cm, O I, C II, Si II , and Fe II. We find velocity windows with absorption from at least one metal and 21 cm, and classify the aligned absorbers into two categories: 'aligned and cospatial absorbers' and 'aligned but not cospatial absorbers'. While 'aligned and cospatial absorbers' originate from overdense structures and can be used to trace gas properties, 'aligned but not cospatial absorbers' are due to peculiar velocity effects. The incidence of absorbers is redshift dependent, as it is dictated by the interplay between reionization and metal enrichment, and shows a peak at z ≈ 8 for the aligned and cospatial absorbers. While aligned but not cospatial absorbers disappear towards the end of reionization because of the lack of an ambient 21 cm forest, aligned and cospatial absorbers are associated with overdense pockets of neutral gas that can be found at lower redshift. We produce mock observations for a set of sightlines for the next generation of telescopes like the ELT and SKA1-LOW, finding that given a sufficiently bright background quasar, these telescopes will be able to detect both types of absorbers throughout reionization. [ABSTRACT FROM AUTHOR]

We use a set of three-dimensional (3D) radiative transfer simulations to study the effect that a large fraction of binary stars in galaxies during the epoch of reionization has on the physical properties of the intergalactic medium (i.e. the gas temperature and the ionization state of hydrogen and helium), on the topology of the ionized bubbles and on the 21 cm power spectra. Consistently to previous literature, we find that the inclusion of binary stars can speed up the reionization process of H  i and He  i , while He  ii reionization is still dominated by more energetic sources, especially accreting black holes. The earlier ionization attained with binary stars allows for more time for cooling and recombination so that gas fully ionized by binary stars is typically colder than gas ionized by single stars at any given redshift. With the same volume averaged ionization fraction, the inclusion of binary stars results in fewer small ionized bubbles and more large ones, with visible effects also on the large scales of the 21 cm power spectrum. [ABSTRACT FROM AUTHOR]

The presence of charged dust grains is known to have a profound impact on the physical evolution of the multiphase interstellar medium (ISM). Despite its importance, this process is still poorly explored in numerical simulations due to its complex physics and the tight dependence on the environment. Here, we introduce a novel implementation of grain charging in the cosmological radiative transfer code crash. We first benchmark the code predictions on a series of idealized dusty H  ii regions created by a single star, in order to assess the impact of grain properties on the resulting spatial distribution of charges. Secondly, we perform a realistic radiative transfer simulation of a star-forming region extracted from a dusty galaxy evolving in the Epoch of Reionization. We find that ∼13 per cent of the total dust mass gets negatively charged, mainly silicate and graphite grains of radius 10−3  |$\mu$| m. A complex spatial distribution of grain charges is also found, primarily depending on the exposure to stellar radiation and strongly varying along different lines of sight, as a result of radiative transfer effects. We finally assess the impact of grain properties (both chemical composition and size) on the resulting charge distribution. The new implementation described here will open up a wide range of possible studies investigating the physical evolution of the dusty ISM, nowadays accessible to observations of high- and low- redshift galaxies. [ABSTRACT FROM AUTHOR]

We present a definitive assessment of the role of inverse Compton scattering of cosmic microwave background photons (IC/CMB) in the context of radio galaxies. Owing to the steep increase of the CMB radiation energy density, IC/CMB is supposed to become progressively more important with respect to radio synchrotron cooling as the redshift increases. For typical energies at play, this process will up-scatter the CMB photons into the X-ray band, and is thus expected to yield a redshift-dependent, concurrent X-ray brightening and radio dimming of the jet-powered structures. Here, we show how a conclusive proof of this effect hinges on high-resolution imaging data in which the extended lobes can be distinguished from the compact hotspots where synchrotron self-Compton dominates the X-ray emission regardless of redshift. We analyse Chandra and Very Large Array data of 11 radio galaxies between |$1.3 \lesssim z \lesssim 4.3$|⁠ , and demonstrate that the emission from their lobes is fully consistent with the expectations from IC/CMB in equipartition. Once the dependence on size and radio luminosity are properly accounted for, the measured lobe X-ray luminosities bear the characteristic ∝(1 + z)4 proportionality expected of a CMB seed radiation field. Whereas this effect can effectively quench the (rest-frame) GHz radio emission from |$z \gtrsim 3$| radio galaxies below |${\lesssim}$| 1 mJy, IC/CMB alone cannot be responsible for a deficit in high- z , radio-loud active galactic nuclei (AGNs) if – as we argue – such AGNs typically have bright, compact hotspots. [ABSTRACT FROM AUTHOR]

The Murchison Widefield Array (MWA) team has derived new upper limits on the spherically averaged power spectrum of the 21-cm signal at six redshifts in the range z ≈ 6.5–8.7. We use these upper limits and a Bayesian inference framework to derive constraints on the ionization and thermal state of the intergalactic medium (IGM) as well as on the strength of a possible additional radio background. We do not find any constraints on the state of the IGM for z ≳ 7.8 if no additional radio background is present. In the presence of such a radio background, the 95 per cent credible intervals of the disfavoured models at redshift ≳ 6.5 correspond to an IGM with a volume-averaged fraction of ionized regions below 0.6 and an average gas temperature ≲ 103 K. In these models, the heated regions are characterized by a temperature larger than that of the radio background, and by a distribution with characteristic size |$\lesssim 10\, h^{-1}$| Mpc and a full width at half maximum (FWHM) of |$\lesssim 30\, h^{-1}$| Mpc. Within the same credible interval limits, we exclude an additional radio background of at least |$0.008{{\ \rm per\ cent}}$| of the CMB at 1.42 GHz. [ABSTRACT FROM AUTHOR]

Using the latest upper limits on the 21-cm power spectrum at z ≈ 9.1 from the Low Frequency Array (LOFAR), we explore the regions of parameter space which are inconsistent with the data. We use 21cmmc , a Monte Carlo Markov chain sampler of 21cmfast which directly forward models the three dimensional (3D) cosmic 21-cm signal in a fully Bayesian framework. We use the astrophysical parametrization from 21cmfast , which includes mass-dependent star formation rates and ionizing escape fractions as well as soft-band X-ray luminosities to place limits on the properties of the high- z galaxies. Further, we connect the disfavoured regions of parameter space with existing observational constraints on the Epoch of Reionization such as ultra-violet (UV) luminosity functions, background UV photoionization rate, intergalactic medium (IGM) neutral fraction, and the electron scattering optical depth. We find that all models exceeding the 21-cm signal limits set by LOFAR at z ≈ 9.1 are excluded at ≳2 σ by other probes. Finally, we place limits on the IGM spin temperature from LOFAR, disfavouring at 95 per cent confidence spin temperatures below ∼2.6 K across an IGM neutral fraction range of |$0.15 \lesssim \bar{x}_{\rm H\, \rm {\small I}} \lesssim 0.6$|⁠. Note, these limits are only obtained from 141 h of data in a single redshift bin. With tighter upper limits, across multiple redshift bins expected in the near future from LOFAR, more viable models will be ruled out. Our approach demonstrates the potential of forward modelling tools such as 21cmmc in combining 21-cm observations with other high- z probes to constrain the astrophysics of galaxies. [ABSTRACT FROM AUTHOR]

To investigate the potential abundance and impact of nuclear black holes (BHs) during reionization, we generate a neural network that estimates their masses and accretion rates by training it on 23 properties of galaxies harbouring them at z  = 6 in the cosmological hydrodynamical simulation MassiveBlack-II. We then populate all galaxies in the simulation from z  = 18 to 5 with BHs from this network. As the network allows to robustly extrapolate to BH masses below those of the BH seeds, we predict a population of faint BHs with a turnover-free luminosity function, while retaining the bright (and observed) BHs, and together they predict a Universe in which intergalactic hydrogen is |$15{{\ \rm per\ cent}}$| ionized at z  = 6 for a clumping factor of 5. Faint BHs may play a stronger role in H reionization without violating any observational constraints. This is expected to have an impact also on pre-heating and pre-ionization, which is relevant to observations of the 21-cm line from neutral H. We also find that BHs grow more efficiently at higher z , but mainly follow a redshift-independent galaxy–BH relation. We provide a power law parametrization of the hydrogen ionizing emissivity of BHs. [ABSTRACT FROM AUTHOR]

We present simulations of cosmic reionization and reheating from z  = 18 to z  = 5, investigating the role of stars (emitting soft UV-photons), nuclear black holes (BHs, with power-law spectra), X-ray binaries (XRBs, with hard X-ray dominated spectra), and the supernova-associated thermal bremsstrahlung of the diffuse interstellar medium (ISM, with soft X-ray spectra). We post-process the hydrodynamical simulation MassiveBlack-II (MBII) with multifrequency ionizing radiative transfer. The source properties are directly derived from the physical environment of MBII, and our only real free parameter is the ionizing escape fraction f esc. We find that, among the models explored here, the one with an escape fraction that decreases with decreasing redshift yields results most in line with observations, such as of the neutral hydrogen fraction and the Thomson scattering optical depth. Stars are the main driver of hydrogen reionization and consequently of the thermal history of the intergalactic medium (IGM). We obtain 〈 x H  ii 〉 = 0.99998 at z  = 6 for all source types, with volume-averaged temperatures |$\langle \, T \rangle \sim 20\,000$|  K. BHs are rare and negligible to hydrogen reionization, but conversely they are the only sources that can fully ionize helium, increasing local temperatures by ∼104 K. The thermal and ionization state of the neutral and lowly ionized hydrogen differs significantly with different source combinations, with ISM and (to a lesser extent) XRBs, playing a significant role and, as a consequence, determining the transition from absorption to emission of the 21-cm signal from neutral hydrogen. [ABSTRACT FROM AUTHOR]

We introduce a versatile and spatially resolved morphological characterization of binary fields, rooted in the opening transform of mathematical morphology. We subsequently apply it to the thresholded ionization field in simulations of cosmic reionization and study the morphology of ionized regions. We find that an ionized volume element typically resides in an ionized region with radius ∼8  h −1 cMpc at the midpoint of reionization (z ≈ 7.5) and follow the bubble size distribution even beyond the overlap phase. We find that percolation of the fully ionized component sets in when 25 per cent of the universe is ionized and that the resulting infinite cluster incorporates all ionized regions above ∼8  h −1 cMpc. We also quantify the clustering of ionized regions of varying radius with respect to matter and on small scales detect the formation of superbubbles in the overlap phase. On large scales, we quantify the bias values of the centres of ionized and neutral regions of different sizes and not only show that the largest ones at the high-point of reionization can reach b ≈ 30, but also that early small ionized regions are positively correlated with matter and large neutral regions and late small ionized regions are heavily antibiased with respect to matter, down to b ≲ −20. [ABSTRACT FROM AUTHOR]

We report on deep Chandra X-ray Telescope imaging observations of 4C 63.20, one of the few known radio galaxies at z > 3.5. The X-ray counterpart is resolved into a core plus two off-nuclear sources that (combined) account for close to 30 per cent of the total X-ray flux. Their morphology and orientation are consistent with a diffuse, lobe-like nature, albeit compact hotspots cannot be ruled out. The broad-band spectral energy distribution of 4C 63.20 can be reproduced with a jet model where the majority of the radio flux can be ascribed to synchrotron emission from the hotspots, whereas the (non-nuclear) X-ray emission is produced via inverse Compton (IC) off of cosmic microwave background (CMB) photons within the extended lobes. This scenario is broadly consistent with the expectation from highly magnetized lobes in a hotter CMB, and supports the view that IC/CMB may quench less extreme radio lobes at high redshifts. [ABSTRACT FROM AUTHOR]

The hyperfine transition of 3He+ at 3.5 cm has been thought as a probe of the high- z IGM, since it offers a unique insight into the evolution of the helium component of the gas, as well as potentially give an independent constraint on the 21 cm signal from neutral hydrogen. In this paper, we use radiative transfer simulations of reionization driven by sources such as stars, X-ray binaries, accreting black holes and shock heated interstellar medium, and simulations of a high- z quasar to characterize the signal and analyse its prospects of detection. We find that the peak of the signal lies in the range ∼1–50  μ K for both environments, but while around the quasar it is always in emission, in the case of cosmic reionization a brief period of absorption is expected. As the evolution of He  ii is determined by stars, we find that it is not possible to distinguish reionization histories driven by more energetic sources. On the other hand, while a bright QSO produces a signal in 21 cm that is very similar to the one from a large collection of galaxies, its signature in 3.5 cm is very peculiar and could be a powerful probe to identify the presence of the QSO. We analyse the prospects of the signal's detectability using SKA1-mid as our reference telescope. We find that the noise power spectrum dominates over the power spectrum of the signal, although a modest signal-to-noise ratio can be obtained when the wavenumber bin width and the survey volume are sufficiently large. [ABSTRACT FROM AUTHOR]

The Square Kilometre Array (SKA) is expected to provide the first tomographic observations of the neutral intergalactic medium at redshifts z > 6 and pinpoint the locations of individual ionized bubbles during early stages of cosmic reionization. In scenarios where star-forming galaxies provide most of the ionizing photons required for cosmic reionization, one expects the first ionized bubbles to be centred on overdensities of such galaxies. Here, we model the properties of galaxy populations within isolated, ionized bubbles that SKA-1 should be able to resolve at z ≈ 7–10, and explore the prospects for galaxy counts within such structures with various upcoming near-infrared telescopes. We find that, for the bubbles that are within reach of SKA-1 tomography, the bubble volume is closely tied to the number of ionizing photons that have escaped from the galaxies within. In the case of galaxy-dominated reionization, galaxies are expected to turn up above the spectroscopic detection threshold of JWST and ELT in even the smallest resolvable bubbles at z ≤ 10. The prospects of detecting galaxies within these structures in purely photometric surveys with Euclid, WFIRST, JWST , or ELT are also discussed. While spectroscopy is preferable towards the end of reionization to provide a robust sample of bubble members, multiband imaging may be a competitive option for bubbles at z ≈ 10, due to the very small number of line-of-sight interlopers expected at these redshifts. [ABSTRACT FROM AUTHOR]

In this paper, we use radiative transfer+ N -body simulations to explore the feasibility of measurements of cross-correlations between the 21-cm field observed by the Square Kilometre Array (SKA) and high- |$z$| Lyman α emitters (LAEs) detected in galaxy surveys with the Subaru Hyper Suprime-Cam (HSC), Subaru Prime Focus Spectrograph (PFS), and Wide Field Infrared Survey Telescope (WFIRST). 21cm–LAE cross-correlations are in fact a powerful probe of the epoch of reionization as they are expected to provide precious information on the progress of reionization and the typical scale of ionized regions at different redshifts. The next generation observations with SKA will have a noise level much lower than those with its precursor radio facilities, introducing a significant improvement in the measurement of the cross-correlations. We find that an SKA-HSC/PFS observation will allow to investigate scales below ∼10 and ∼60  h −1 Mpc at |$z$|  = 7.3 and 6.6, respectively. WFIRST will allow to access also higher redshifts, as it is expected to observe spectroscopically ∼900 LAEs per deg2 and unit redshift in the range 7.5 ≤ |$z$| ≤ 8.5. Because of the reduction of the shot noise compared to HSC and PFS, observations with WFIRST will result in more precise cross-correlations and increased observable scales. [ABSTRACT FROM AUTHOR]

We study statistics of the 21-cm signal from the epoch of reionization. We propose to use [O  iii ] line emitting galaxies to cross-correlate with the 21-cm signal from z = 7–10. To this aim, we employ simulations of reionization obtained post-processing the high-resolution cosmological hydrodynamic simulation Massive Black-II with the three-dimensional (3D) radiative transfer code crash to follow the propagation of ionizing photons from a variety of sources. We show that, during the early phases of reionization, the 21-cm signal is positively correlated with the spatial distribution of the [O  iii ] emitters on large scales |$(k \lt 1\, h~\rm cMpc^{-1})$|⁠. This positive correlation is generated by the temperature–galaxy correlation and it is a few times larger than when we assume that the heating is saturated. As the reionized regions expand, the correlation changes its sign to negative from z = 10 to 8. The signals at this epoch can be detected by combining the Square Kilometre Array (SKA) and a wide-field [O  iii ] emitter survey. We also calculate the cross-power spectrum with a 3D [O  iii ] intensity field, aiming at exploiting future intensity mapping observations. We conclude that high-redshift [O  iii ] line emitters can be used to probe the reionization process when the intergalactic medium is largely neutral. [ABSTRACT FROM AUTHOR]

Galactic outflows are critical to our understanding of galaxy formation and evolution. However, the details of the underlying feedback process remain unclear. We compare Ly α observations of the circumgalactic medium (CGM) of Lyman Break Galaxies (LBGs) with mock observations of their simulated CGM. We use cosmological hydrodynamical 'zoom-in' simulations of an LBG which contains strong, momentum-driven galactic outflows. Simulation snapshots at |$z$|  = 2.2 and |$z$|  = 2.65 are used, corresponding to the available observational data. The simulation is post-processed with the radiative transfer code crash to account for the impact of ionizing photons on hydrogen gas surrounding the simulated LBG. We generate mock absorption line maps for comparison with data derived from observed close galaxy–galaxy pairs. We perform calculations of Ly α photons scattering through the CGM with our newly developed Monte Carlo code slaf, and compare to observations of diffuse Ly α haloes around LBGs. Our fiducial galactic outflow model comes closer to reproducing currently observed characteristics of the CGM in Ly α than a reference inefficient feedback model used for comparison. Nevertheless, our fiducial model still struggles to reproduce the observed data of the inner CGM (at impact parameter b < 30 kpc). Our results suggest that galactic outflows affect Ly α absorption and emission around galaxies mostly at impact parameters b < 50 kpc, while cold accretion flows dominate at larger distances. We discuss the implications of this result, and underline the potential constraining power of CGM observations – in emission and absorption – on galactic outflow models. [ABSTRACT FROM AUTHOR]

We present a new dust extension to the Monte Carlo radiative transfer code crash, which enables it to simulate the propagation of ionizing radiation through mixtures of gas and dust. The new code is applied to study the impact of dust absorption on idealized galactic H  ii regions and on small-scale reionization. We find that H  ii regions are reduced in size by the presence of dust, while their inner temperature and ionization structure remain largely unaffected. In the small-scale reionization simulation, dust hardens ionization fronts and delays the overlap of ionized bubbles. This effect is found to depend only weakly on the assumed abundance of dust in underdense regions. [ABSTRACT FROM AUTHOR]

With the seeding prescription in MassiveBlack-II, BHs do not contribute significantly to either ionization or heating. With only stars, most of the IGM remains in a cold state (with a median T = 11K at z = 10), however, the presence of more energetic sources raises the temperature of regions around the brightest and more clustered sources above that of the cosmic microwave background, opening the possibility to observing the 21 cm signal in emission. [ABSTRACT FROM AUTHOR]

Recent results have suggested that active galactic nuclei (AGN) could provide enough photons to reionize the Universe. We assess the viability of this scenario using a semi-numerical framework for modelling reionization, to which we add a quasar contribution by constructing a Quasar Halo Occupancy Distribution (QHOD) based on Giallongo et al. observations. Assuming a constant QHOD, we find that an AGN-only model cannot simultaneously match observations of the optical depth τe, neutral fraction and ionizing emissivity. Such a model predicts τ e too low by ~2σ relative to Planck constraints, and reionizes the Universe at z ~ 5. Arbitrarily increasing the AGN emissivity to match these results yields a strong mismatch with the observed ionizing emissivity at z ~ 5. If we instead assume a redshift-independent AGN luminosity function yielding an emissivity evolution like that assumed in Madau & Haardt model, then we can match τe albeit with late reionization; however, such evolution is inconsistent with observations at z ~ 4-6 and poorly motivated physically. These results arise because AGN are more biased towards massive haloes than typical reionizing galaxies, resulting in stronger clustering and later formation times. AGN-dominated models produce larger ionizing bubbles that are reflected in ~×2 more 21 cm power on all scales. A model with equal part galaxies and AGN contribution is still (barely) consistent with observations, but could be distinguished using next-generation 21 cm experiments such as Hydrogen Epoch of Reionization Array and SKA-low. We conclude that, even with recent claims of more faint AGN than previously thought, AGN are highly unlikely to dominate the ionizing photon budget for reionization. [ABSTRACT FROM AUTHOR]

We introduce a novel technique, called 'granulometry', to characterize and recover the mean size and the size distribution of HII regions from 21-cm tomography. The technique is easy to implement, but places the previously not very well-defined concept of morphology on a firm mathematical foundation. The size distribution of the cold spots in 21-cm tomography can be used as a direct tracer of the underlying probability distribution of HII region sizes. We explore the capability of the method using large-scale reionization simulations and mock observational data cubes while considering capabilities of SquareKilometreArray 1 (SKA1) lowand a future extension to SKA2. We show that the technique allows the recovery of the HII region size distribution with a moderate signal-to-noise ratio from wide-field imaging (SNR ≲ 3), for which the statistical uncertainty is sample variance dominated. We address the observational requirements on the angular resolution, the field of view, and the thermal noise limit for a successful measurement. To achieve a full scientific return from 21-cm tomography and to exploit a synergy with 21-cm power spectra, we suggest an observing strategy using wide-field imaging (several tens of square degrees) by an interferometric mosaicking/multibeam observation with additional intermediate baselines (~2-4 km) in an SKA phase 2. [ABSTRACT FROM AUTHOR]

We present a detailed analysis of the ionization and thermal structure of the intergalactic medium (IGM) around a high-redshift (z = 10) QSO, using a large suite of cosmological, multifrequency radiative transfer simulations, exploring the contribution from galaxies as well as the QSO, and the effect of X-rays and secondary ionization. We show that in high-z QSO environments both the central QSO and the surrounding galaxies concertedly control the reionization morphology of hydrogen and helium and have a non-linear impact on the thermal structure of the IGM. A QSO imprints a distinctive morphology on HII regions if its total ionizing photon budget exceeds that of the surrounding galaxies since the onset of hydrogen reionization; otherwise, the morphology shows little difference from that of HII regions produced only by galaxies. In addition, the spectral shape of the collective radiation field from galaxies and QSOs controls the thickness of the I-fronts. While a UV-obscured QSO can broaden the I-front, the contribution from other UV sources, either galaxies or unobscured QSOs, is sufficient to maintain a sharp I-front. X-ray photons from the QSO are responsible for a prominent extended tail of partial ionization ahead of the I-front. QSOs leave a unique imprint on the morphology of He II/He III regions. We suggest that, while the physical state of the IGM is modified by QSOs, the most direct test to understand the role of galaxies and QSOs during reionization is to perform galaxy surveys in a region of sky imaged by 21 cm tomography. [ABSTRACT FROM AUTHOR]

In an effort to understand the cause of the apparent depletion in the number density of radio-loud active galactic nuclei (AGNs) at z > 3, this work investigates the viability of the so-called cosmic microwave background (CMB) quenching mechanism of intrinsically jetted, high-z AGNs, whereby inverse Compton scattering of CMB photons off electrons within the extended lobes results in a substantial dimming of the lobe synchrotron emission at GHz frequencies, while simultaneously boosting their diffuse X-ray signal. We focus on five z > 3.5 radio galaxies that have sufficiently deep Chandra exposure (>50 ks) to warrant a meaningful investigation of any extended X-ray emission. For those objects with evidence for statistically significant extended X-ray lobes (4C 41.17 and 4C 03.24), we combine the Chandra measurements with literature data at lower frequencies to assemble the systems' spectral energy distributions (SEDs), and utilize state-of-the-art SED modelling - including emission from the disc, torus, jet, hotspots and lobes - to infer their physical parameters. For both radio galaxies, the magnetic energy density in the hotspots is found to exceed the energy density in CMB photons, whereas the opposite is true for the lobes. This implies that any extended synchrotron emission likely originates from the hotspots themselves, rather than the lobes. Conversely, inverse Compton scattering of CMB photons dominates the extended X-ray emission from the lobes, which are effectively 'radio-quenched'. As a result, CMB quenching is effective in these systems in spite of the fact that the observed X-ray to radio luminosity ratio does not bear the signature (1 + z)4 dependence of the CMB energy density. [ABSTRACT FROM AUTHOR]

The visibility of Lya-emitting galaxies during the Epoch of Reionization is controlled by both diffuse HI patches in large-scale bubble morphology and small-scale absorbers. To investigate their impacts on Lyα transfer, we apply a novel combination of analytic modelling and cosmological hydrodynamical, radiative transfer simulations to three reionization models: (i) the 'bubble' model, where only diffuse HI outside ionized bubbles is present; (ii) the 'web' model, where HI exists only in overdense self-shielded gas; and (iii) the hybrid 'web-bubble' model. The three models can explain the observed Lyα luminosity function equally well, but with very different HI fractions. This confirms a degeneracy between the ionization topology of the intergalactic medium (IGM) and theHI fraction inferred from Lyα surveys. We highlight the importance of the clustering of small-scale absorbers around galaxies. Acombined analysis of the Lyα luminosity function and the Lyα fraction can break this degeneracy and provide constraints on the reionization history and its topology. Constraints can be improved by analysing the full MUV-dependent redshift evolution of the Lyα fraction of Lyman break galaxies. We find that the IGM-transmission probability distribution function is unimodal for bubble models and bimodal in web models. Comparing our models to observations, we infer that the neutral fraction at z ~ 7 is likely to be of the order of tens of per cent when interpreted with bubble or web-bubble models, with a conservative lower limit ~1 per cent when interpreted with web models. [ABSTRACT FROM AUTHOR]

We attempt to interpret existing data on the evolution of the UV luminosity function and UV colours, β, of galaxies at 5 ≤ z ≤ 8, to improve our understanding of their dust content and interstellar medium properties. To this aim, we post-process the results of a cosmological hydrodynamical simulation with a chemical evolution model, which includes dust formation by supernovae and intermediate-mass stars, dust destruction in supernova shocks, and grain growth by accretion of gas-phase elements in dense gas. We find that observations require a steep, Small Magellanic Cloud-like extinction curve and a clumpy dust distribution, where stellar populations younger than 15 Myr are still embedded in their dusty natal clouds. Investigating the scatter in the colour distribution and stellar mass, we find that the observed trends can be explained by the presence of two populations: younger, less massive galaxies where dust enrichment is mainly due to stellar sources, and massive, more chemically evolved ones, where efficient grain growth provides the dominant contribution to the total dust mass. Computing the IR-excess--UV colour relation, we find that all but the dustiest model galaxies follow a relation shallower than the Meurer et al. one, usually adopted to correct the observed UV luminosities of high-z galaxies for the effects of dust extinction. As a result, their total star formation rates might have been overestimated. Our study illustrates the importance to incorporate a proper treatment of dust in simulations of high-z galaxies, and that massive, dusty, UV-faint galaxies might have already appeared at z ... 7. [ABSTRACT FROM AUTHOR]

The 21 cm-galaxy cross-power spectrum is expected to be one of the promising probes of the Epoch of Reionization (EoR), as it could offer information about the progress of reionization and the typical scale of ionized regions at different redshifts. With upcoming observations of 21 cm emission from the EoR with the Low Frequency Array (LOFAR), and of high-redshift Ly α emitters with Subaru's Hyper Suprime-Cam (HSC), we investigate the observability of such cross-power spectrum with these two instruments, which are both planning to observe the ELAIS-N1 field at z = 6.6. In this paper, we use N-body + radiative transfer (both for continuum and Ly α photons) simulations at redshift 6.68, 7.06 and 7.3 to compute the 3D theoretical 21 cm-galaxy cross-power spectrum and cross-correlation function, as well as to predict the 2D 21 cm-galaxy cross-power spectrum and cross-correlation function expected to be observed by LOFAR and HSC. Once noise and projection effects are accounted for, our predictions of the 21 cm-galaxy cross-power spectrum show clear anti-correlation on scales larger than ~60 h-1 Mpc (corresponding to k ~ 0.1 h Mpc-1), with levels of significance p = 0.003 at z = 6.6 and p = 0.08 at z = 7.3. On smaller scales, instead, the signal is completely contaminated. On the other hand, our 21 cm-galaxy cross-correlation function is strongly contaminated by noise on all scales, since the noise is no longer being separated by its k modes. [ABSTRACT FROM AUTHOR]

The observed 21 cm signal from the epoch of reionization will be distorted along the line of sight by the peculiar velocities of matter particles. These redshift-space distortions will affect the contrast in the signal and will also make it anisotropic. This anisotropy contains information about the cross-correlation between the matter density field and the neutral hydrogen field, and could thus potentially be used to extract information about the sources of reionization. In this paper, we study a collection of simulated reionization scenarios assuming different models for the sources of reionization. We show that the 21 cm anisotropy is best measured by the quadrupole moment of the power spectrum. We find that, unless the properties of the reionization sources are extreme in some way, the quadrupole moment evolves very predictably as a function of global neutral fraction. This predictability implies that redshiftspace distortions are not a very sensitive tool for distinguishing between reionization sources. However, the quadrupole moment can be used as a model-independent probe for constraining the reionization history. We show that such measurements can be done to some extent by first-generation instruments such as LOFAR, while the SKA should be able to measure the reionization history using the quadrupole moment of the power spectrum to great accuracy. [ABSTRACT FROM AUTHOR]

We explore the impact of Fermi-like acceleration of Lyman α (Ly α) photons across shock fronts on the observed Ly α spectral line shape. We first confirm the result of Neufeld & McKee (1988) that this mechanism gives rise to extended blue wings which may have been observed in some radio galaxies. Our Monte Carlo radiative transfer calculations further show that in a minor modification of the shell model, in which we add an additional static shell of hydrogen, this process can naturally explain the small blue bumps observed in a subset of Ly α-emitting galaxies, which have been difficult to explain with conventional shell models. Blue bumps can be produced with an additional column density of static hydrogen as small as Nstatic HI ⪡ Nshell HI, and typically occur at roughly the outflow velocity of the shell. In our model the spectra of so-called blue-bump objects might reflect an evolutionary stage in which the outflows regulating the escape of Ly α photons are still engulfed within a static interstellar medium. [ABSTRACT FROM AUTHOR]

Estimating the intergalactic medium ionization level of a region needs proper treatment of the reionization process for a large representative volume of the universe. The clumping factor, a parameter which accounts for the effect of recombinations in unresolved, small-scale structures, aids in achieving the required accuracy for the reionization history even in simulations with low spatial resolution. In this paper, we study for the first time the redshift evolution of clumping factors of different ionized species of H and He in a small but very high resolution simulation of the reionization process. We investigate the dependence of the value and redshift evolution of clumping factors on their definition, the ionization level of the gas, the grid resolution, box size and mean dimensionless density of the simulations. [ABSTRACT FROM PUBLISHER]

Several experiments are underway to detect the cosmic-redshifted 21-cm signal from neutral hydrogen from the Epoch of Reionization (EoR). Due to their very low signal-to-noise ratio, these observations aim for a statistical detection of the signal by measuring its power spectrum. We investigate the extraction of the variance of the signal as a first step towards detecting and constraining the global history of the EoR. Signal variance is the integral of the signal's power spectrum, and it is expected to be measured with a high significance. We demonstrate this through results from a simulation and parameter estimation pipeline developed for the Low-Frequency Array (LOFAR)-EoR experiment. We show that LOFAR should be able to detect the EoR in 600 h of integration using the variance statistic. Additionally, the redshift (zr) and duration (Δz) of reionization can be constrained assuming a parametrization. We use an EoR simulation of zr = 7.68 and Δz = 0.43 to test the pipeline. We are able to detect the simulated signal with a significance of four standard deviations and extract the EoR parameters as $z_{\rm r} = 7.72^{+0.37}_{-0.18}$ and $\Delta z = 0.53^{+0.12}_{-0.23}$ in 600 h, assuming that systematic errors can be adequately controlled. We further show that the significance of detection and constraints on EoR parameters can be improved by measuring the cross-variance of the signal by cross-correlating consecutive redshift bins. [ABSTRACT FROM PUBLISHER]

ABSTRACT We propose to use high-redshift long γ-ray bursts (GRBs) as cosmological tools to constrain the amount of primordial non-Gaussianity in the density field. By using numerical, N-body, hydrodynamic, chemistry simulations of different cosmological volumes with various Gaussian and non-Gaussian models, we self-consistently relate the cosmic star formation rate density to the corresponding GRB rate. Assuming that GRBs are fair tracers of cosmic star formation, we find that positive local non-Gaussianities, described in terms of the non-linear parameter, fNL, might boost significantly the GRB rate at high redshift, z ≫ 6. Deviations with respect to the Gaussian case account for a few orders of magnitude if fNL ∼ 1000, one order of magnitude for fNL ∼ 100 and a factor of ∼2 for fNL ∼ 50. These differences are found only at large redshift, while at later times the rates tend to converge. Furthermore, a comparison between our predictions and the observed GRB data at z > 6 allows us to exclude large negative fNL, consistently with previous works. Future detections of any long GRB at extremely high redshift ( z ∼ 15-20) could favour non-Gaussian scenarios with positive fNL. More stringent constraints require much larger high- z GRB complete samples, currently not available in the literature. By distinguishing the contributions to the GRB rate from the metal-poor Population III regime, and the metal-enriched Population II-I regime, we conclude that the latter is a more solid tracer of the underlying matter distribution, while the former is strongly dominated by feedback mechanisms from the first, massive, short-lived stars, rather than by possible non-Gaussian fluctuations. This holds quite independently of the assumed Population III initial mass function. [ABSTRACT FROM AUTHOR]

ABSTRACT We perform a systematic study of how the inhomogeneities in the intergalactic medium (IGM) affect the observability of Lyα emitters (LAEs) around the epoch of reionization. We focus on the IGM close to the galaxies as the detailed ionization distribution and velocity fields of this region could significantly influence the scattering of Lyα photons off neutral H atoms as they traverse the IGM after escaping from the galaxy. We simulate the surface brightness (SB) maps and spectra of more than 100 LAEs at z = 7.7 as seen by an observer at z = 0. To achieve this, we extract the source properties of galaxies and their surrounding IGM from cosmological simulations of box sizes 5-30 h−1 Mpc and then follow the coupled radiative transfer of ionizing and Lyα radiation through the IGM using crashα. We find that the simulated SB profiles are extended and their detailed structure is affected by inhomogeneities in the IGM, especially at high neutral fractions. The detectability of LAEs and the fraction of the flux observed depend heavily on the shape of the SB profile and the SB threshold (SB th) of the observational campaign. Only ultradeep observations (e.g. [ABSTRACT FROM AUTHOR]

We study cosmological simulations of early structure formation, including non-equilibrium molecular chemistry, metal pollution from stellar evolution, transition from Population III (PopIII) to Population II (PopII) star formation, regulated by a given critical metallicity, and feedback effects. We perform analyses of the properties of the gas, and use the PopIII and PopII populations as tracers of the metallicity. This allows us to investigate the properties of early metal spreading from the different stellar populations and its interplay with pristine molecular gas, in terms of the initial mass function and critical metallicity. We find that, independently of the details about PopIII modelling, after the onset of star formation, regions enriched below the critical level are mostly found in isolated environments, while PopII star formation regions are much more clumped. Typical star-forming haloes, at , with masses between and , show average supernova (SN) driven outflow rates of up to in enriched gas, initially leaving the original star formation regions almost devoid of metals. The polluted material, which is gravitationally incorporated in overdense environments on time-scales of , is mostly coming from external, nearby star-forming sites ('gravitational enrichment'). In parallel, the pristine-gas inflow rates are some orders of magnitudes larger, between ∼10 and . However, thermal feedback from SN destroys molecules within the pristine gas hindering its ability to cool and to condense into high-density star-forming regions. Only the polluted material incorporated via gravitational enrichment can continue to cool by atomic fine-structure transitions on short time-scales, short enough to end the initial PopIII regime within less than . Moreover, the interplay between the pristine, cold, infalling gas and the ejected, hot, metal-rich gas leads to turbulent Reynolds numbers of the order of , and contributes to the suppression of pristine inflow rates into the densest, star-forming regions. [ABSTRACT FROM AUTHOR]

Tseliakhovich and Hirata recently discovered that higher order corrections to the cosmological linear-perturbation theory lead to supersonic coherent baryonic flows just after recombination (i.e. ), with rms velocities of ∼30 km s relative to the underlying dark matter distribution, on comoving scales of Mpc . To study the impact of these coherent flows, we performed high-resolution N-body plus smoothed particle hydrodynamic simulations in boxes of 5.0 and 0.7 Mpc , for bulk-flow velocities of 0 (as reference), 30 and 60 km s. The simulations follow the evolution of cosmic structures by taking into account detailed, primordial, non-equilibrium gas chemistry (i.e. H, He, H, HD, HeH, etc.), cooling, star formation and feedback effects from stellar evolution. We find that these bulk flows suppress star formation in low-mass haloes (i.e. until ), lower the abundance of the first objects by per cent and as a consequence delay cosmic star formation history by yr. The gas fractions in individual objects can change by up to a factor of 2 at very early times. Coherent bulk flow therefore has implications for (i) the star formation in the lowest-mass haloes (e.g. dSphs); (ii) the start of reionization by suppressing it in some patches of the Universe; and (iii) the heating (i.e. spin temperature) of neutral hydrogen. We speculate that the patchy nature of reionization and heating on several Mpc scales could lead to enhanced differences in the H spin temperature, giving rise to stronger variations in the H brightness temperatures during the late dark ages. [ABSTRACT FROM AUTHOR]

We present results from the first cosmological simulations which study the onset of primordial, metal-free (population III), cosmic star formation and the transition to the present-day, metal-rich star formation (population II-I), including molecular (H2, HD, etc.) evolution, tracing the injection of metals by supernovæ (SNe) into the surrounding intergalactic medium and following the change in the initial mass function (IMF) according to the metallicity of the corresponding stellar population. Our investigation addresses the role of a wide variety of parameters (critical metallicity for the transition, IMF slope and range, SN/pair-instability SN metal yields, star formation threshold, resolution, etc.) on the metal-enrichment history and the associated transition in the star formation mode. All simulations present common trends. Metal enrichment is very patchy, with rare, unpolluted regions surviving at all redshifts, inducing the simultaneous presence of metal-free and metal-rich star formation regimes. As a result of the rapid pollution within high-density regions due to the first SN/pair-instability SN, local metallicity is quickly boosted above the critical metallicity for the transition. For this reason, population III stars dominate only during the very first stages of structure formation, with an average contribution to the total star formation rate that reaches a constant value of at redshift . If primordial supenovæ consisted only of type II ones, the contribution would be . Interestingly, the above conclusions are independent from many poorly constrained parameters. [ABSTRACT FROM AUTHOR]

One of the aims of the Low Frequency Array (LOFAR) Epoch of Reionization (EoR) project is to measure the power spectrum of variations in the intensity of redshifted 21-cm radiation from the EoR. The sensitivity with which this power spectrum can be estimated depends on the level of thermal noise and sample variance, and also on the systematic errors arising from the extraction process, in particular from the subtraction of foreground contamination. We model the extraction process using realistic simulations of the cosmological signal, the foregrounds and noise, and so estimate the sensitivity of the LOFAR EoR experiment to the redshifted 21-cm power spectrum. Detection of emission from the EoR should be possible within 360 h of observation with a single station beam. Integrating for longer, and synthesizing multiple station beams within the primary (tile) beam, then enables us to extract progressively more accurate estimates of the power at a greater range of scales and redshifts. We discuss different observational strategies which compromise between depth of observation, sky coverage and frequency coverage. A plan in which lower frequencies receive a larger fraction of the time appears to be promising. We also study the nature of the bias which foreground fitting errors induce on the inferred power spectrum and discuss how to reduce and correct for this bias. The angular and line-of-sight power spectra have different merits in this respect, and we suggest considering them separately in the analysis of LOFAR data. [ABSTRACT FROM AUTHOR]

We discuss expectations for the absorption of high-energy gamma-rays by pair production with intergalactic radiation fields (IRFs) at very high redshifts ( ), and the prospects thereof for probing the cosmic reionization era. For the evolving IRF, a semi-analytical model incorporating both Population II and Population III stars is employed, which is consistent with a wide variety of existing high- z observations including quasi-stellar object spectral measurements, Wilkinson Microwave Anisotropy Probe Thomson depth constraints, near-infrared source count limits, etc. We find that the ultraviolet IRF below the Lyman edge energy with intensities in the range of a few times can cause appreciable attenuation above ∼12 GeV at , down to ∼6–8 GeV at . This may be observable in the spectra of blazars or gamma-ray bursts by the Fermi Gamma-ray Space Telescope or next-generation facilities such as the Cherenkov Telescope Array, Advanced Gamma-ray Imaging System or 5@5, providing invaluable insight into early star formation and cosmic reionization. [ABSTRACT FROM AUTHOR]

We study the statistical properties of the cosmological 21-cm signal from both the intergalactic medium (IGM) and minihaloes, using a reionization simulation that includes a self-consistent treatment of minihalo photoevaporation. We consider two models for minihalo formation and three typical thermal states of the IGM – heating purely by ionization, heating from both ionizing and Lyα photons and a maximal ‘strong heating’ model. We find that the signal from the IGM is almost always dominant over that from minihaloes. In our calculation, the differential brightness temperature, of minihaloes is never larger than 2 mK. Although there are indeed some differences in the signals from the minihaloes and from the IGM, even with the planned generation of radio telescopes it will be unfeasible to detect them. However, minihaloes significantly affect the ionization state of the IGM and the corresponding 21-cm flux. [ABSTRACT FROM AUTHOR]

One of the problems facing experiments designed to detect redshifted 21-cm emission from the epoch of reionization (EoR) is the presence of foregrounds which exceed the cosmological signal in intensity by orders of magnitude. While fitting them so that they can be removed, we must be careful to minimize ‘overfitting’, in which we fit away some of the cosmological signal, and ‘underfitting’, in which real features of the foregrounds cannot be captured by the fit, polluting the signal reconstruction. We argue that in principle it would be better to fit the foregrounds non-parametrically – allowing the data to determine their shape – rather than selecting some functional form in advance and then fitting its parameters. Non-parametric fits often suffer from other problems, however. We discuss these before suggesting a non-parametric method, Wp smoothing, which seems to avoid some of them. After outlining the principles of Wp smoothing, we describe an algorithm used to implement it. Some useful results for implementing an alternative algorithm are given in an appendix. We apply Wp smoothing to a synthetic data cube for the Low Frequency Array (LOFAR) EoR experiment. This cube includes realistic models for the signal, foregrounds, instrumental response and noise. The performance of Wp smoothing, measured by the extent to which it is able to recover the variance of the cosmological signal and to which it avoids the fitting residuals being polluted by leakage of power from the foregrounds, is compared to that of a parametric fit, and to another non-parametric method (smoothing splines). We find that Wp smoothing is superior to smoothing splines for our application, and is competitive with parametric methods even though in the latter case we may choose the functional form of the fit with advance knowledge of the simulated foregrounds. Finally, we discuss how the quality of the fit is affected by the frequency resolution and range, by the characteristics of the cosmological signal and by edge effects. [ABSTRACT FROM AUTHOR]

Detecting redshifted 21-cm emission from neutral hydrogen in the early Universe promises to give direct constraints on the epoch of reionization (EoR). It will, though, be very challenging to extract the cosmological signal (CS) from foregrounds and noise which are orders of magnitude larger. Fortunately, the signal has some characteristics which differentiate it from the foregrounds and noise, and we suggest that using the correct statistics may tease out signatures of reionization. We generate mock data cubes simulating the output of the Low Frequency Array (LOFAR) EoR experiment. These cubes combine realistic models for Galactic and extragalactic foregrounds and the noise with three different simulations of the CS. We fit out the foregrounds, which are smooth in the frequency direction, to produce residual images in each frequency band. We denoise these images and study the skewness of the one-point distribution in the images as a function of frequency. We find that, under sufficiently optimistic assumptions, we can recover the main features of the redshift evolution of the skewness in the 21-cm signal. We argue that some of these features – such as a dip at the onset of reionization, followed by a rise towards its later stages – may be generic, and give us a promising route to a statistical detection of reionization. [ABSTRACT FROM AUTHOR]

We present an efficient method to generate large simulations of the epoch of reionization without the need for a full three-dimensional radiative transfer code. Large dark-matter-only simulations are post-processed to produce maps of the redshifted 21-cm emission from neutral hydrogen. Dark matter haloes are embedded with sources of radiation whose properties are either based on semi-analytical prescriptions or derived from hydrodynamical simulations. These sources could either be stars or power-law sources with varying spectral indices. Assuming spherical symmetry, ionized bubbles are created around these sources, whose radial ionized fraction and temperature profiles are derived from a catalogue of one-dimensional radiative transfer experiments. In case of overlap of these spheres, photons are conserved by redistributing them around the connected ionized regions corresponding to the spheres. The efficiency with which these maps are created allows us to span the large parameter space typically encountered in reionization simulations. We compare our results with other, more accurate, three-dimensional radiative transfer simulations and find excellent agreement for the redshifts and the spatial scales of interest to upcoming 21-cm experiments. We generate a contiguous observational cube spanning redshift 6 to 12 and use these simulations to study the differences in the reionization histories between stars and quasars. Finally, the signal is convolved with the Low Frequency Array (LOFAR) beam response and its effects are analysed and quantified. Statistics performed on this mock data set shed light on possible observational strategies for LOFAR. [ABSTRACT FROM AUTHOR]

We evaluate the broad-band afterglow emission of very high redshift gamma-ray bursts (GRBs) using standard relativistic blast-wave models with both forward and reverse shock components. For a broad range of parameters, a generic property for GRBs at redshifts is that the emission peaks in the millimetre to far-infrared (far-IR) bands with milli-Jansky flux levels, first at a few hours after the burst due to the reverse shock, and then again for several days afterwards with somewhat lower flux due to the forward shock. The radio, submillimetre and IR continuum emission should be readily detectable out to by the Atacama Large Millimetre Array (ALMA), Extended Very Large Array, Square Kilometre Array (SKA) and other facilities. For relatively bright bursts, spectroscopic measurements of molecular and atomic absorption lines due to ambient protostellar gas may be possible. Utilizing models of primordial protostellar clouds, we show that under certain conditions, appreciable absorption may be caused by HD rotational transitions even in metal-free environments. After sufficient metal enrichment, absorption from CO rotational transitions and [O i] fine-structure transitions can also become strong. With appropriate observing strategies in combination with optical telescopes, ALMA and/or SKA may be able to detect such lines, offering a unique probe of physical conditions in individual Population III (Pop III) and early Pop II star-forming regions. We also remark on potential near-IR absorption features due to electronic transitions of H2. [ABSTRACT FROM AUTHOR]

One of the most-outstanding problems in the gravitational collapse scenario of early structure formation is the cooling of primordial gas to allow for small-mass objects to form. As the neutral primordial gas is a poor radiator at temperatures , molecular hydrogen is needed for further cooling down to temperatures . The formation of molecular hydrogen is catalyzed by the presence of free electrons, which could be provided by the ionization due to an early population of cosmic rays (CRs). In order to investigate this possibility, we developed a code to study the effects of ionizing CRs on the thermal and chemical evolution of primordial gas. We found that CRs can provide enough free electrons needed for the formation of molecular hydrogen, and therefore can increase the cooling ability of such primordial gas under following conditions. A dissociating photon flux with , initial temperature of the gas , total gas number densities , and cosmic-ray sources with . [ABSTRACT FROM AUTHOR]

Radiative transfer (RT) simulations are now at the forefront of numerical astrophysics. They are becoming crucial for an increasing number of astrophysical and cosmological problems; at the same time their computational cost has come within reach of currently available computational power. Further progress is retarded by the considerable number of different algorithms (including various flavours of ray tracing and moment schemes) developed, which makes the selection of the most suitable technique for a given problem a non-trivial task. Assessing the validity ranges, accuracy and performances of these schemes is the main aim of this paper, for which we have compared 11 independent RT codes on five test problems: (0) basic physics; (1) isothermal H ii region expansion; (2) H ii region expansion with evolving temperature; (3) I-front trapping and shadowing by a dense clump and (4) multiple sources in a cosmological density field. The outputs of these tests have been compared and differences analysed. The agreement between the various codes is satisfactory although not perfect. The main source of discrepancy appears to reside in the multifrequency treatment approach, resulting in different thicknesses of the ionized-neutral transition regions and the temperature structure. The present results and tests represent the most complete benchmark available for the development of new codes and improvement of existing ones. To further this aim all test inputs and outputs are made publicly available in digital form. [ABSTRACT FROM AUTHOR]

The morphology of the total gas and the neutral hydrogen (H i) distributions during the cosmological epoch of reionization can be quantified with Minkowski functionals (MFs) of isodensity surfaces. We compute the MFs from the output of a high-resolution numerical simulation which includes explicit treatment of transfer of ultraviolet (UV) ionizing radiation. ‘Galaxies’ identified in the simulation using semi-analytic models of galaxy formation are assumed to be the sole sources of UV photons. The MFs of the total gas distribution are well described by the analytic expressions derived for lognormal random fields. The statistical properties of the diffuse H i depend on the gas distribution and on the way ionized regions propagate in the intergalactic medium (IGM). The deviations of the MFs of the H i distribution from those of a lognormal random field are, therefore, caused by reionization. We use the MFs to discriminate between the various stages of reionization in the simulation. We suggest a simple model of reionization which reproduces the MFs derived from this simulation. Using random realizations of lognormal density fields, we also assess the ability of MFs to distinguish between different reionization scenarios. Our results are relevant to the analysis of future cosmological 21-cm maps. [ABSTRACT FROM AUTHOR]

Motivated by theoretical predictions that the first stars were predominantly very massive, we investigate the physics of the transition from an early epoch dominated by massive Pop III stars to a later epoch dominated by familiar low-mass Pop II/I stars by means of a numerically generated catalogue of dark matter haloes coupled with a self-consistent treatment of chemical and radiative feedback. Depending on the strength of the chemical feedback, Pop III stars can contribute a substantial fraction (several per cent) of the cosmic star formation activity even at moderate redshifts, . We find that the three sources tentatively detected in Near Infrared Camera and Multi-Object Spectrometer (NICMOS) Ultra Deep Fields (UDFs) should be powered by Pop III stars, if these are massive; however, this scenario fails to reproduce the derived Wilkinson Microwave Anisotropy Probe ( WMAP) electron scattering optical depth. Instead, both the UDFs and WMAP constraints can be fulfilled if stars at any time form with a more standard, slightly top-heavy, Larson initial mass function. [ABSTRACT FROM AUTHOR]