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

We compare various foreground removal techniques that are being utilized to remove bright foregrounds in various experiments aiming to detect the redshifted 21 cm signal of neutral hydrogen from the epoch of reionization. In this work, we test the performance of removal techniques (FastICA, GMCA, and GPR) on 10 nights of LOFAR data and investigate the possibility of recovering the latest upper limit on the 21 cm signal. Interestingly, we find that GMCA and FastICA reproduce the most recent 2σ upper limit of |$\Delta ^2_{21} \lt $| (73)2 mK2 at k  = 0.075  h cMpc−1, which resulted from the application of GPR. We also find that FastICA and GMCA begin to deviate from the noise-limit at k -scales larger than ∼0.1  h cMpc−1. We then replicate the data via simulations to see the source of FastICA and GMCA's limitations, by testing them against various instrumental effects. We find that no single instrumental effect, such as primary beam effects or mode-mixing, can explain the poorer recovery by FastICA and GMCA at larger k -scales. We then test scale-independence of FastICA and GMCA, and find that lower k -scales can be modelled by a smaller number of independent components. For larger scales (k ≳ 0.1  h cMpc−1), more independent components are needed to fit the foregrounds. We conclude that, the current usage of GPR by the LOFAR collaboration is the appropriate removal technique. It is both robust and less prone to overfitting, with future improvements to GPR's fitting optimization to yield deeper limits. [ABSTRACT FROM AUTHOR]

The ARCADE2 and LWA1 experiments have claimed an excess over the cosmic microwave background (CMB) at low radio frequencies. If the cosmological high-redshift contribution to this radio background is between 0.1 per cent and 22 per cent of the CMB at 1.42 GHz, it could explain the tentative EDGES low-band detection of the anomalously deep absorption in the 21-cm signal of neutral hydrogen. We use the upper limit on the 21-cm signal from the Epoch of Reionization (z  = 9.1) based on 141 h of observations with LOFAR to evaluate the contribution of the high-redshift Universe to the detected radio background. Marginalizing over astrophysical properties of star-forming haloes, we find (at 95 per cent CL) that the cosmological radio background can be at most 9.6 per cent of the CMB at 1.42 GHz. This limit rules out strong contribution of the high-redshift Universe to the ARCADE2 and LWA1 measurements. Even though LOFAR places limit on the extra radio background, excess of 0.1–9.6 per cent over the CMB (at 1.42 GHz) is still allowed and could explain the EDGES low-band detection. We also constrain the thermal and ionization state of the gas at z  = 9.1, and put limits on the properties of the first star-forming objects. We find that, in agreement with the limits from EDGES high-band data, LOFAR data constrain scenarios with inefficient X-ray sources, and cases where the Universe was ionized by stars in massive haloes only. [ABSTRACT FROM AUTHOR]

The recent discovery of high-redshift dusty galaxies implies a rapid dust enrichment of their interstellar medium (ISM). To interpret these observations, we run a cosmological simulation in a 30 h −1 cMpc/size volume down to z ≈ 4. We use the hydrodynamical code dustygadget , which accounts for the production of dust by stellar populations and its evolution in the ISM. We find that the cosmic dust density parameter (Ωd) is mainly driven by stellar dust at z ≳ 10, so that mass- and metallicity-dependent yields are required to assess the dust content in the first galaxies. At z ≲ 9, the growth of grains in the ISM of evolved systems [log(M ⋆/M⊙) > 8.5] significantly increases their dust mass, in agreement with observations in the redshift range 4 ≲ z < 8. Our simulation shows that the variety of high-redshift galaxies observed with the Atacama Large Millimeter Array can naturally be accounted for by modelling the grain growth time-scale as a function of the physical conditions in the gas cold phase. In addition, the trends of dust-to-metal and dust-to-gas (⁠|${\cal D}$|⁠) ratios are compatible with the available data. A qualitative investigation of the inhomogeneous dust distribution in a representative massive halo at z ≈ 4 shows that dust is found from the central galaxy up to the closest satellites along polluted filaments with |$\rm log({\cal D}) \le -2.4$|⁠ , but sharply declines at distances d ≳ 30 kpc along many lines of sight, where |$\rm log({\cal D}) \lesssim -4.0$|⁠. [ABSTRACT FROM AUTHOR]

We derive constraints on the thermal and ionization states of the intergalactic medium (IGM) at redshift ≈ 9.1 using new upper limits on the 21-cm power spectrum measured by the LOFAR radio telescope and a prior on the ionized fraction at that redshift estimated from recent cosmic microwave background (CMB) observations. We have used results from the reionization simulation code grizzly and a Bayesian inference framework to constrain the parameters which describe the physical state of the IGM. We find that, if the gas heating remains negligible, an IGM with ionized fraction ≳0.13 and a distribution of the ionized regions with a characteristic size ≳ 8  h −1 comoving megaparsec (Mpc) and a full width at half-maximum (FWHM) ≳16  h −1 Mpc is ruled out. For an IGM with a uniform spin temperature T S ≳ 3 K, no constraints on the ionized component can be computed. If the large-scale fluctuations of the signal are driven by spin temperature fluctuations, an IGM with a volume fraction ≲0.34 of heated regions with a temperature larger than CMB, average gas temperature 7–160 K, and a distribution of the heated regions with characteristic size 3.5–70 h −1 Mpc and FWHM of ≲110 h −1 Mpc is ruled out. These constraints are within the 95 per cent credible intervals. With more stringent future upper limits from LOFAR at multiple redshifts, the constraints will become tighter and will exclude an increasingly large region of the parameter space. [ABSTRACT FROM AUTHOR]

We investigate the impact of quasars on the ionization of the surrounding intergalactic medium (IGM) with the radiative transfer code  crash 4, now accounting for X-rays and secondary electrons. After comparing with analytic solutions, we post-process a cosmic volume (≈1.5 × 104 Mpc3  h −3) containing a ULAS J1120+0641-like quasar (QSO) hosted by a 5 × 1011 M⊙  h −1 dark matter (DM) halo. We find that (i) the average H  ii region (R ∼ 3.2 pMpc in a lifetime t f = 107 yr) is mainly set by UV flux, in agreement with semi-analytic scaling relations; (ii) a largely neutral ($$x_{\rm{H\,\small {II}}} < 0.001$$), warm (T ∼ 103 K) tail extends up to few Mpc beyond the ionization front, as a result of the X-ray flux; and (iii) LyC-opaque inhomogeneities induce a line of sight (LOS) scatter in R as high as few physical Mpc, consistent with the DLA scenario proposed to explain the anomalous size of the ULAS J1120+0641 ionized region. On the other hand, with an ionization rate $$\dot{N}_{\gamma ,0} \sim 10^{57}$$ s−1, the assumed DLA clustering and gas opacity, only one LOS shows an H  ii region compatible with the observed one. We deduce that either the ionization rate of the QSO is at least one order of magnitude lower or the ULAS J1120+0641 bright phase is shorter than 107 yr. [ABSTRACT FROM AUTHOR]

We introduce CRASH-AMR, a new version of the cosmological radiative transfer (RT) code CRASH, enabled to use refined grids. This new feature allows us to attain higher resolution in our RT simulations and thus to describe more accurately ionization and temperature patterns in high-density regions. We have tested CRASH-AMR by simulating the evolution of an ionized region produced by a single source embedded in gas at constant density, as well as by a more realistic configuration of multiple sources in an inhomogeneous density field. While we find an excellent agreement with the previous version of CRASH when the adaptive mesh refinement (AMR) feature is disabled, showing that no numerical artefact has been introduced in CRASHAMR, when additional refinement levels are used the code can simulate more accurately the physics of ionized gas in high-density regions. This result has been attained at no computational loss, as RT simulations onAMRgrids with maximum resolution equivalent to that of a uniform Cartesian grid can be run with a gain of up to 60 per cent in computational time. [ABSTRACT FROM AUTHOR]

We investigate signatures of Population III (PopIII) stars in the metal-enriched environment of gamma-ray bursts (GRBs) originating from Population II-I (PopII/I) stars by using abundance ratios derived from numerical simulations that follow stellar evolution and chemical enrichment. We find that at z > 10 more than 10 per cent of PopII/I GRBs explode in a medium previously enriched by PopIII stars (we refer to them as GRBII↎III). Although the formation of GRBII→III is more frequent than that of pristine PopIII GRBs (GRBIIIs), we find that the expected GRBII→III observed rate is comparable to that of GRBIIIs, due to the usually larger luminosities of the latter. GRBII→III events take place preferentially in small protogalaxies with stellar masses M* ~ 104.5-107 M⊙, star formation rates SFR ~10-3-10-1M⊙yr-1 and metallicities Z ~ 10-4-10-2 Z⊙. On the other hand, galaxies with Z < 10-2.8 Z⊙ are dominated by metal enrichment from PopIII stars and should preferentially host GRBII→III. Hence, measured GRB metal content below this limit could represent a strong evidence of enrichment by pristine stellar populations. We discuss how to discriminate PopIII metal enrichment on the basis of various abundance ratios observable in the spectra of GRBs' afterglows. By employing such analysis, we conclude that the currently known candidates at redshift z ≃ 6 - i.e. GRB 050904 and GRB 130606A - are likely not originated in environments pre-enriched by PopIII stars. Abundance measurements for GRBs at z ≃ 5 - such as GRB 100219A and GRB 111008A - are still poor to draw definitive conclusions, although their hosts seem to be dominated by PopII/I pollution and do not show evident signatures of massive PopIII pre-enrichment. [ABSTRACT FROM AUTHOR]

Here we introduce crash3, the latest release of the 3D radiative transfer code crash. In its current implementation, crash3 integrates into the reference algorithm the code cloudy to evaluate the ionization states of metals, self-consistently with the radiative transfer through H and He. The feedback of the heavy elements on the calculation of the gas temperature is also taken into account, making crash3 the first 3D code for cosmological applications which treats self-consistently the radiative transfer through an inhomogeneous distribution of metal-enriched gas with an arbitrary number of point sources and/or a background radiation. The code has been tested in idealized configurations, as well as in a more realistic case of multiple sources embedded in a polluted cosmic web. Through these validation tests, the new method has been proven to be numerically stable and convergent. We have studied the dependence of the results on a number of physical quantities such as the source characteristics (spectral range and shape, intensity), the metal composition, the gas number density and metallicity. [ABSTRACT FROM AUTHOR]

In this paper, we examine the effect of X-ray and Lyα photons on the intergalactic medium (IGM) temperature. We calculate the photon production from a population of stars and microquasars in a set of cosmological hydrodynamic simulations which self-consistently follow the dark matter dynamics, radiative processes as well as star formation, black hole (BH) growth and associated feedback processes. We find that (i) IGM heating is always dominated by X-rays unless the Lyα photon contribution from stars in objects with mass becomes significantly enhanced with respect to the X-ray contribution from BHs in the same halo (which we do not directly model). (ii) Without overproducing the unresolved X-ray background, the gas temperature becomes larger than the CMB temperature, and thus an associated 21-cm signal should be expected in emission, at . We discuss how in such a scenario the transition redshift between a 21-cm signal in absorption and in emission could be used to constraint BHs accretion and associated feedback processes. [ABSTRACT FROM AUTHOR]

In this paper, we report on the improvements implemented in the cosmological radiative transfer codecrash. In particular, we present a new multi-frequency algorithm for spectra sampling which makes use of coloured photon packets: we discuss the need for the multi-frequency approach, describe its implementation and present the improvedcrash performance in reproducing the effects of ionizing radiation with an arbitrary spectrum. We further discuss minor changes in the code implementation which allow for more efficient performance and an increased precision. [ABSTRACT FROM AUTHOR]

Future high-redshift 21-cm experiments will suffer from a high degree of contamination, due both to astrophysical foregrounds and to non-astrophysical and instrumental effects. In order to reliably extract the cosmological signal from the observed data, it is essential to understand very well all data components and their influence on the extracted signal. Here we present simulated astrophysical foregrounds data cubes and discuss their possible statistical effects on the data. The foreground maps are produced assuming 5°× 5° windows that match those expected to be observed by the LOFAR epoch of reionization (EoR) key science project. We show that with the expected LOFAR–EoR sky and receiver noise levels, which amount to ≈52 mK at 150 MHz after 400 h of total observing time, a simple polynomial fit allows a statistical reconstruction of the signal. We also show that the polynomial fitting will work for maps with realistic yet idealized instrument response, i.e. a response that includes only a uniform uv coverage as a function of frequency and ignores many other uncertainties. Polarized Galactic synchrotron maps that include internal polarization and a number of Faraday screens along the line of sight are also simulated. The importance of these stems from the fact that the LOFAR instrument, in common with all current interferometric EoR experiments, has an instrumentally polarized response. [ABSTRACT FROM AUTHOR]

In this paper, we have calculated the effect of Lyα photons emitted by the first stars on the evolution of the intergalactic medium (IGM) temperature. We have considered both a standard Salpeter IMF and a delta-function IMF for very massive stars with mass . We find that the Lyα photons produced by the stellar populations considered here are able to heat the IGM at z≲ 25, although never above ∼100 K. Stars with a Salpeter IMF are more effective as, due to the contribution from small-mass long-living stars, they produce a higher Lyα background. Lyα heating can affect the subsequent formation of small-mass objects by producing an entropy floor that may limit the amount of gas able to collapse and reduce the gas clumping. We find that the gas fraction in haloes of mass below is less than 50 per cent (for the smallest masses this fraction drops to 1 per cent or less) compared to a case without Lyα heating. Finally, Lyα photons heat the IGM temperature above the cosmic microwave background temperature and render the 21-cm line from neutral hydrogen visible in emission at z≲ 15. [ABSTRACT FROM AUTHOR]

Cooling is the main process leading to the condensation of gas in the dark matter potential wells and consequently to star and structure formation. In a metal-free environment, the main available coolants are H, He, H2 and HD; once the gas is enriched with metals, these also become important in defining the cooling properties of the gas. We discuss the implementation ingadget-2 of molecular and metal cooling at temperatures lower than 104 K, following the time-dependent properties of the gas and pollution from stellar evolution. We have checked the validity of our scheme by comparing the results of some test runs with previous calculations of cosmic abundance evolution and structure formation, finding excellent agreement. We have also investigated the relevance of molecule and metal cooling in some specific cases, finding that inclusion of HD cooling results in a higher clumping factor of the gas at high redshifts, while metal cooling at low temperatures can have a significant impact on the formation and evolution of cold objects. [ABSTRACT FROM AUTHOR]

One of the most debated issues in the theoretical modelling of cosmic reionization is the impact of small-mass gravitationally bound structures. We carry out the first numerical investigation of the role of such sterile ‘minihaloes’ (MHs), which serve as self-shielding screens of ionizing photons. MHs are too small to be properly resolved in current large-scale cosmological simulations, and thus we estimate their effects using a subgrid model, considering two cases that bracket their effect within this framework. In the ‘extreme-suppression’ case in which MH formation ceases once a region is partially ionized, their effect on cosmic reionization is modest, reducing the volume-averaged ionization fraction by an overall factor of less than15 per cent. In the other extreme, in which MH formation is never suppressed, they delay complete reionization as much as , in rough agreement with the results from a previous semi-analytical study by the authors. Thus, depending on the details of the MH formation process, their effect on the overall progress of reionization can range from modest to significant, but the MH photon consumption is by itself insufficient to force an extended reionization epoch. [ABSTRACT FROM AUTHOR]

We study cosmic microwave background (CMB) secondary anisotropies produced by inhomogeneous reionization by means of cosmological simulations coupled with the radiative transfer codecrash. The reionization history is consistent with the Wilkinson Microwave Anisotropy Probe Thomson optical depth determination. We find that the signal arising from this process dominates over the primary CMB component for and reaches a maximum amplitude of on arcmin scales (i.e. l as large as several thousands). We then cross-correlate secondary CMB anisotropy maps with neutral hydrogen 21-cm line emission fluctuations obtained from the same simulations. The two signals are highly anticorrelated on angular scales corresponding to the typical size of H ii regions (including overlapping) at the 21-cm map redshift. We show how the CMB/21-cm cross-correlation can be used: (i) to study the nature of the reionization sources; (ii) to reconstruct the cosmic reionization history; (iii) to infer the mean cosmic ionization level at any redshift. We discuss the feasibility of the proposed experiment with forthcoming facilities. [ABSTRACT FROM AUTHOR]

Cites a study published in 'Mon. Not. R. Astrom. Soc.,' which studies intergalactic medium reionization process in it's full cosmological context, including structure evolution and realistic galaxy population. Effect of environment in reionization process; Factors involved in proper treatment of reionization process.

Discusses the result of the study of the inhomogeneous (IGM) reionization due to an inhomogeneous distribution of stellar sources. Application of the Gunn-Peterson test to QSO absorption spectra; Evidence on the existence of quasars and galaxies; Predictions on the masses of the objects formed first.

We calculate the expected mid-infrared (MIR) molecular hydrogen line emission from the first objects in the Universe. As a result of their low masses, the stellar feedback from massive stars is able to blow away their gas content and collect it into a cooling shell where H[sub 2] rapidly forms and IR roto-vibrational (as for example the rest-frame 2.12 μm) lines carry away a large fraction (up to 10 per cent) of the explosion energy. The fluxes from these sources are in the range 10[sup -21]–10[sup -17] erg s[sup -1] cm[sup -2]. The highest number counts are expected in the 20-μm band, where about 10[sup 5] sources deg[sup -2] are predicted at the limiting flux of 3×10[sup -18] erg s[sup -1] cm[sup -2]. Among the planned observational facilities, we find that the best detection perspectives are offered by the Next Generation Space Telescope (NGST), which should be able to reveal about 200 first objects in one hour observation time at its limiting flux in the above band. Therefore, mid-IR instruments appear to represent perfect tools to trace star formation and stellar feedback in the high (z&gsim;5) redshift Universe. [ABSTRACT FROM AUTHOR]

We use numerical simulations of cosmic reionization and radiative processes related to the H i 21-cm emission line to produce synthetic radio maps as seen by next-generation telescopes that will operate at low radio frequencies (e.g. the Low Frequency Array, LOFAR). Two different scenarios, in which the end of reionization occurs early ( z≈ 13) or late ( z≈ 8) depending on the initial mass function (IMF) of the first stars and ionizing photon escape fraction, have been explored. For each of these models we produce synthetic H i 21-cm emission maps by convolving the simulation outputs with the provisional LOFAR sampling function in the frequency range 76–140 MHz. If reionization occurs late, LOFAR will be able to detect individual H i structures on arcmin scales, emitting at a brightness temperature of ≈35 mK as a 3σ signal in about 1000 h of observing time. In the case of early reionization, the detection would be unlikely, due to decreased sensitivity and increased sky temperatures. These results assume that ionospheric, interference and foreground issues are fully under control. [ABSTRACT FROM AUTHOR]

Large-scale polarization of the cosmic microwave background measured by the WMAP satellite requires a mean optical depth to Thomson scattering, τ[SUBe] ∼ 0.17. The reionization of the Universe must therefore have begun at relatively high redshift. We have studied the reionization process using supercomputer simulations of a large and representative region of a universe which has cosmological parameters consistent with the WMAP results (Ω[SUBm] = 0.3, Ω[SUBA] = 0.7, h = 0.7, Ω[SUBb] = 0.04, n = 1 and σ[SUB8] = 0.9). Our simulations follow both the radiative transfer of ionizing photons and the formation and evolution of the galaxy population which produces them. A previously published model with ionizing photon production as expected for zero-metallicity stars distributed according to a standard stellar initial mass function (IMF) (10[SUP61] photons per unit solar mass of formed stars) and with a moderate photon escape fraction from galaxies (5 per cent), produces τ[SUBe] = 0.104, which is within 1.0 to 1.5σ of the best WMAP value. Values of up to 0.16 can be produced by taking larger escape fractions or a top-heavy IMF. The data do not require a separate populations of miniquasars or of stars forming in objects with total masses below 10[SUP9] M[SUB⊙]. Reconciling such early reionization with the observed Gunn--Peterson troughs in z > 6 quasars may be challenging. Possible resolutions of this problem are discussed. [ABSTRACT FROM AUTHOR]