Search

J1316+2614 at z = 3.613 is the UV-brightest (MUV = −24.7) and strongest Lyman continuum-emitting (fescLyC ≈ 90%) star-forming galaxy known; it also shows signatures of inflowing gas from its blue-dominated Lyα profile. We present high-resolution imaging with the Hubble Space Telescope (HST) and the Very Large Telescope (VLT) of the LyC, Lyα, rest-UV, and optical emission of J1316+2614. Detailed analysis of the LyC and UV light distributions reveals compact yet resolved profiles, with LyC and UV morphologies showing identical half-light radii of reff ≃ 220 pc. The continuum-subtracted Lyα emission, obtained with the HST ramp-filter FR551N, reveals an extended filamentary structure of ≃6.0 kpc oriented south to north with only residual flux within the stellar core, suggesting a Lyα 'hole'. Our spectral energy distribution analysis shows that J1316+2614 is characterised by a young (5.7 ± 1.0 Myr), nearly un-obscured stellar population with a high star-formation rate (SFR = 898 ± 181 M⊙ yr−1) and a stellar mass of M⋆young = (4.8 ± 0.3) × 109 M⊙. Additionally, the spectral energy distribution analysis supports the absence of an underlying old stellar population (M⋆old ≤ 2.8 × 109 M⊙, 3σ). J1316+2614 presents remarkably high SFR and stellar mass surface densities of log(Σ SFR[M⊙ yr−1 kpc−2]) = 3.47 ± 0.11 and log(ΣM⋆[M⊙pc−2]) = 4.20 ± 0.06, respectively, which are among the highest observed in star-forming galaxies and are more typically observed in local young massive star clusters and globular clusters. Our findings indicate that J1316+2614 is a powerful, young, and compact starburst that is leaking a significant amount of LyC photons due to a lack of gas and dust within the starburst. We explored the conditions for gas expulsion using a simple energetic balance and find that, given the strong binding force in J1316+2614, a high star-formation efficiency (ϵSF ≥ 0.7) is necessary to explain the removal of gas and its exposed nature. Our results thus suggest a close link between high ϵSF and high fescLyC. This high efficiency can also naturally explain the remarkably high SFR, UV luminosity, and efficient mass growth of J1316+2614, which acquired at least 62% of its mass in the last 6 Myr. J1316+2614 may exemplify an intense, feedback-free starburst with a high ϵSF, similar to those proposed for UV-bright galaxies at high redshifts. [ABSTRACT FROM AUTHOR]

The geometry of the neutral gas in and around galaxies is a key regulator of the escape of ionizing photons. We present the first statistical study aimed at linking the neutral and ionized gas distributions to the Lyman continuum (LyC) escape fraction (fescLyC) in a sample of 22 confirmed LyC leakers and non-leakers at z ≈ 0.35 using the Keck Cosmic Web Imager (Keck/KCWI) and the Low Resolution Spectrograph 2 (HET/LRS2). Our integral field unit data enable the detection of neutral and low-ionization gas, as traced by Mg II, and ionized gas, as traced by [O II], extending beyond the stellar continuum for seven and ten objects, respectively. All but one object with extended Mg II emission also show extended [O II] emission; in this case, Mg II emission is always more extended than [O II] by a factor 1.2 on average. Most of the galaxies with extended emission are non or weak LyC leakers (fescLyC < 5%), but we find a large diversity of neutral and low-ionization gas configurations around these weakly LyC-emitting galaxies. Conversely, the strongest leakers (fescLyC > 5%) appear uniformly compact in both Mg II and [O II] with exponential scale lengths ≲1 kpc. Most are unresolved at the resolution of our data. We also find a trend between fescLyC and the spatial offsets of the nebular gas and the stellar continuum emission. Moreover, we find significant anticorrelations between the spatial extent of the neutral and/or low-ionization gas and the [O III]/[O II] ratio, and Hβ equivalent width, as well as positive correlations with metallicity and UV size, suggesting that galaxies with more compact neutral and/or low-ionization gas sizes are more highly ionized. The observations suggest that strong LyC emitters do not have extended neutral and/or low-ionization gas halos and ionizing photons may be emitted in many directions. Combined with high ionization diagnostics, we propose that the Mg II, and potentially [O II], spatial compactness are indirect indicators of LyC emitting galaxies at high redshift. [ABSTRACT FROM AUTHOR]

Finding the first generation of stars formed out of pristine gas in the early Universe, known as Population III (PopIII) stars, is one of the most important goals of modern astrophysics. Recent models have suggested that PopIII stars may form in pockets of pristine gas in the halo of more evolved galaxies. We present NIRSpec integral field spectroscopy and micro-shutter array spectroscopic observations of the region around GN-z11, an exceptionally luminous galaxy at z = 10.6, that reveal a greater than 5σ detection of a feature consistent with being HeIIλ1640 emission at the redshift of GN-z11. The very high equivalent width of the putative HeII emission in this clump (log(EWrest(HeII)/Å) = 1.79−0.25+0.15) and a lack of metal lines can be explained in terms of photoionisation by PopIII stars, while photoionisation by PopII stars is inconsistent with the data. The high equivalent width would also indicate that the putative PopIII stars likely have an initial mass function with an upper cutoff reaching at least 500 M⊙. The PopIII bolometric luminosity inferred from the HeII line would be ∼7 × 109 L⊙, which would imply a total stellar mass formed in the burst of ∼2 × 105 M⊙. We find that photoionisation by the active galactic nucleus (AGN) in GN-z11 cannot account for the HeII luminosity observed in the clump but can potentially be responsible for an additional HeII emission observed closer to GN-z11. We also consider the possibility of in situ photoionisation by an accreting direct collapse black hole hosted by the HeII clump. We find that this scenario is less favoured, but it remains a possible alternative interpretation. We also report the detection of a Lyα halo stemming out of GN-z11 and extending out to ∼2 kpc as well as resolved funnel-shaped CIII emission likely tracing the ionisation cone of the AGN. [ABSTRACT FROM AUTHOR]

Cosmic dawn (CD) and the epoch of reionization (EoR) are the most important parts of cosmic history during which the first luminous structures emerged. These first objects heated and ionized the neutral atomic hydrogen in the intergalactic medium. The redshifted 21-cm radiation from the atomic hydrogen provides an excellent direct probe to study the evolution of neutral hydrogen (Hi) and thus reveal nature of the first luminous objects, their evolution and role in this last phase transition of the Universe and formation and evolution of the structures thereafter. Direct mapping of the Hi density during the CD–EoR is rather difficult with the current and forthcoming instruments due to stronger foreground and other observational contamination. The first detection of this redshifted Hi signal is expected to be done through statistical estimators. Given the upmost importance of the detection and analysis of the redshifted 21-cm signal, physics of CD–EoR is considered as one of the objective of the upcoming SKA-low telescope. This paper summarizes the collective effort of Indian astronomers to understand the origin of the redshifted 21-cm signal, sources of first ionizing photons, their propagation through the IGM, various cosmological effects on the expected 21-cm signal, various statistical measures of the signal like power spectrum, bispectrum, etc. A collective effort on detection of such signal by developing estimators of the statistical measures with rigorous assessment of their expected uncertainties, various challenges like that of the large foreground emission and calibration issues are also discussed. Various versions of the detection methods discussed here have also been used in practice with the Giant Meterwave Radio Telescope with successful assessment of the foreground contamination and upper limits on the matter density in reionization and post-reionization era. The collective efforts compiled here has been a large part of the global effort to prepare proper observational technique, analysis procedure for the first light of the CD–EoR through the SKA-low. [ABSTRACT FROM AUTHOR]

This correction notice addresses some typographical errors in a paper titled "First upper limits on the 21 cm signal power spectrum from cosmic dawn from one night of observations with NenuFAR." The corrections include fixing the units for the color bar in a figure, clarifying the baselines used by LOFAR to compute the power spectrum, and adjusting the caption in another figure. These corrections are only typographical and do not impact the text, results, or conclusions of the paper. The authors of the paper are listed as S. Munshi, F. G. Mertens, L. V. E. Koopmans, A. R. Offringa, B. Semelin, D. Aubert, R. Barkana, A. Bracco, S. A. Brackenhoff, B. Cecconi, E. Ceccotti, S. Corbel, A. Fialkov, B. K. Gehlot, R. Ghara, J. N. Girard, J. M. Grießmeier, C. Höfer, I. Hothi, R. Mériot, M. Mevius, P. Ocvirk, A. K. Shaw, G. Theureau, S. Yatawatta, P. Zarka, and S. Zaroubi. [Extracted from the article]

The key challenge in the observation of the redshifted 21-cm signal from cosmic reionization is its separation from the much brighter foreground emission. Such separation relies on the different spectral properties of the two components, although, in real life, the foreground intrinsic spectrum is often corrupted by the instrumental response, inducing systematic effects that can further jeopardize the measurement of the 21-cm signal. In this paper, we use Gaussian Process Regression to model both foreground emission and instrumental systematics in ∼2 h of data from the Hydrogen Epoch of Reionization Array. We find that a simple co-variance model with three components matches the data well, giving a residual power spectrum with white noise properties. These consist of an 'intrinsic' and instrumentally corrupted component with a coherence scale of 20 and 2.4 MHz, respectively (dominating the line-of-sight power spectrum over scales k∥ ≤ 0.2 h cMpc−1) and a baseline-dependent periodic signal with a period of ∼1 MHz (dominating over k∥ ∼ 0.4–0.8 h cMpc−1), which should be distinguishable from the 21-cm Epoch of Reionization signal whose typical coherence scale is ∼0.8 MHz. [ABSTRACT FROM AUTHOR]

We present an estimation of the reionization optical depth τ from an improved analysis of data from the High Frequency Instrument (HFI) on board the Planck satellite. By using an improved version of the HFI map-making code, we greatly reduce the residual large-scale contamination affecting the data, characterised in, but not fully removed from, the Planck 2018 legacy release. This brings the dipole distortion systematic effect, contaminating the very low multipoles, below the noise level. On large-scale polarization-only data, we measure τ = 0.0566+0.0053 -0.0062 at 68% C.L., reducing the Planck 2018 legacy release uncertainty by ~40%. Within the CDM model, in combination with the Planck large-scale temperature likelihood, and the high- temperature and polarization likelihood, we measure τ = 0.059 ± 0.006 at 68% C.L., which corresponds to a mid-point reionization redshift of zre = 8.14 ± 0.61 at 68% C.L. This estimation of the reionization optical depth with 10% accuracy is the strongest constraint to date. [ABSTRACT FROM AUTHOR]

The cosmological reionization and thermal history, following the recombination epoch and the dark age, can be studied at radio frequencies through the tomographic view offered by the redshifted 21 cm line and the integrated information offered by the diffuse free-free emission, coupled to the Comptonization distortion, which is relevant at higher frequencies. For these types of signals, current theoretical predictions span a wide range of possibilities. The recent EDGES observations of the monopole disagree with the typical standard models and call, if confirmed, for non-standard physical processes and/or for an early population of extragalactic sources producing a remarkable radio background at high redshifts that is almost consistent with the ARCADE 2 claim of a significant excess of cosmic microwave background (CMB) absolute temperature at low frequency. These signatures can be observed both in global (or monopole) signal and fluctuations from very large to small angular scales. The peculiar motion of an observer with respect to an ideal reference frame, at rest with respect to the CMB, produces boosting effects in several observable quantities. They are remarkable in the anisotropy patterns at low multipoles, particularly in the dipole, with frequency spectral behaviours depending on the spectrum of the monopole emission, as previously studied in the context of CMB spectral distortions. We present here a novel investigation of this effect at radio frequencies, aimed at predicting the imprints expected in the redshifted 21 cm line signal and in the diffuse free-free emission plus the Comptonization distortion for several representative models. Furthermore, we consider the same type of signal, but as expected from the cosmological (CMB plus potential astrophysical signals) radio background determining the offset for 21 cm redshifted line. The combination of the four types of signal and their different relevance in the various frequency ranges is studied. This approach of linking monopole and anisotropy analyses, can be applied on all-sky or relatively wide sky coverage surveys as well as to a suitable set of sky patches. By relying only on the quality of interfrequency and relative data calibration, the approach in principle by-passes the need for precise absolute calibration, which is a critical point of current and future radio interferometric facilities. [ABSTRACT FROM AUTHOR]

We have modelled direct collapse of a primordial gas within dark matter haloes in the presence of radiative transfer, in high-resolution zoom-in simulations in a cosmological framework, down to the formation of the photosphere and the central object. Radiative transfer has been implemented in the flux-limited diffusion (FLD) approximation. Adiabatic models were run for comparison. We find that (a) the FLD flow forms an irregular central structure and does not exhibit fragmentation, contrary to adiabatic flow which forms a thick disc, driving a pair of spiral shocks, subject to Kelvin–Helmholtz shear instability forming fragments; (b) the growing central core in the FLD flow quickly reaches ${\sim } 10\, \text{M}_\odot$ and a highly variable luminosity of $10^{38}\text{--}10^{39}\, {\rm erg\, s^{-1}}$ , comparable to the Eddington luminosity. It experiences massive recurrent outflows driven by radiation force and thermal pressure gradients, which mix with the accretion flow and transfer the angular momentum outwards; and (c) the interplay between these processes and a massive accretion, results in photosphere at ∼10 au. We conclude that in the FLD model (1) the central object exhibits dynamically insignificant rotation and slower than adiabatic temperature rise with density; (2) does not experience fragmentation leading to star formation, thus promoting the fast track formation of a supermassive black hole (SMBH) seed; (3) inclusion of radiation force leads to outflows, resulting in the mass accumulation within the central 10−3 pc, which is ∼100 times larger than characteristic scale of star formation. The inclusion of radiative transfer reveals complex early stages of formation and growth of the central structure in the direct collapse scenario of SMBH seed formation. [ABSTRACT FROM AUTHOR]

Pair-instability supernovae (PISNe) are very luminous explosions of massive, low-metallicity stars. They can potentially be observed out to high redshifts due to their high explosion energies, thus providing a probe of the Universe prior to reionization. The near-infrared camera (NIRCam) on board the James Webb Space Telescope is ideally suited for detecting their redshifted ultraviolet emission. We calculate the photometric signature of high-redshift PISNe and derive the optimal detection strategy for identifying their prompt emission and possible afterglow. We differentiate between PISNe and other sources that could have a similar photometric signature, such as active galactic nuclei or high-redshift galaxies. We demonstrate that the optimal strategy, which maximizes the visibility time of the PISN light curve per invested exposure time, consists of the two wide-band filters F200W and F356W with an exposure time of 600 s. For such exposures, we expect one PISN at $z$ ≲ 7.5 per at least 50000 different field of view, which can be accomplished with parallel observations and an extensive archival search. The PISN afterglow, caused by nebular emission and reverberation, is very faint and requires unfeasibly long exposure times to be uniquely identified. However, this afterglow would be visible for several hundred years, about two orders of magnitude longer than the prompt emission, rendering PISNe promising targets for future, even more powerful telescopes. [ABSTRACT FROM AUTHOR]

The massive stars that ionized the Universe have short lifetimes and can only be studied near the time of formation, but any low-mass stars that formed contemporaneously might be observable in the local Universe today. We study the abundance pattern and spatial distribution of these ‘siblings of reionizers’ (SoRs) in the eagle cosmological hydrodynamical simulation. SoRs tend to be enriched to supersolar levels in α-elements compared to iron, and we investigate the resemblance between SoRs and obthe served stars that are enhanced in carbon. In eagle galaxies resembling the Milky Way, ∼40 per cent of carbon-enhanced metal poor (CEMP) stars are SoRs. Conversely, ∼10 per cent of all SoRs are CEMP stars. This fraction increases to ≳50 per cent for SoRs of metallicity [Fe/H] < −4, and at such low metallicities, most of the CEMP stars are of CEMP-no subtype that are lacking neutron capture elements. Although these numbers may well depend on the details of the physical models implemented in eagle, the trends we describe are robust as they result from the strong feedback from star formation in early galaxies, itself a key ingredient of most current models of galaxy formation. We further find that most SoRs today reside in haloes with mass Mh  $\stackrel{\text{>}}\approx$  1012 M⊙, and 50 per cent of them are in the halo of their central galaxy (distance >10 kpc), mainly because they were accreted onto their current host rather than formed in situ. To a good approximation, the SoRs are CEMP-no stars that reside in the stellar haloes of massive galaxies, with nearly half of them contributing to the intracluster light in groups and clusters. [ABSTRACT FROM AUTHOR]

The reionization of the Universe ends the dark ages that started after the recombination era. In the case of H, reionization finishes around z ~ 6. Faint star-forming galaxies are the best candidate sources of the H-ionizing radiation, although active galactic nuclei may have also contributed. We have explored whether the termination regions of the jets from active galactic nuclei may have contributed significantly to the ionization of H in the late reionization epoch, around z ~ 6−7. We assumed that, as it has been proposed, active galactic nuclei at z ~ 6 may have presented a high jet fraction, accretion rate, and duty cycle, and that non-thermal electrons contribute significantly to the pressure of jet termination regions. Empirical black-hole mass functions were adopted to characterize the population of active galactic nuclei. From all this, estimates were derived for the isotropic H-ionizing radiation produced in the jet termination regions, at z ~ 6, through inverse Compton scattering off CMB photons. We find that the termination regions of the jets of active galactic nuclei may have radiated most of their energy in the form of H-ionizing radiation at z ~ 6. For typical black-hole mass functions at that redshift, under the considered conditions (long-lasting, common, and very active galactic nuclei with jets), the contribution of these jets to maintain (and possibly enhance) the ionization of H may have been non-negligible. We conclude that the termination regions of jets from active galactic nuclei could have had a significant role in the reionization of the Universe at z ≳ 6. [ABSTRACT FROM AUTHOR]

Contamination due to foregrounds (Galactic and extragalactic), calibration errors, and ionospheric effects poses major challenges in the detection of the cosmic 21 cm signal in various epoch of reionization (EoR) experiments. We present the results of a pilot study of a field centred on 3C196 using LOFAR (LOw Frequency ARray) low-band (56–70MHz) observations, where we quantify various wide field and calibration effects such as gain errors, polarized foregrounds, and ionospheric effects. We observe a 'pitchfork' structure in the 2D power spectrum of the polarized intensity in delay-baseline space, which leaks into the modes beyond the instrumental horizon [EoR/CD (cosmic dawn) window]. We show that this structure largely arises due to strong instrumental polarization leakage ( ${\sim }30\hbox{ per cent}$ ) towards Cas A (∼21 kJy at 81 MHz, brightest source in northern sky), which is far away from primary field of view. We measure an extremely small ionospheric diffractive scale (rdiff ≈ 430 m at 60 MHz) towards Cas A resembling pure Kolmogorov turbulence compared to rdiff∼  3−20 km towards zenith at 150 MHz for typical ionospheric conditions. This is one of the smallest diffractive scales ever measured at these frequencies. Our work provides insights in understanding the nature of aforementioned effects and mitigating them in future CD observations (e.g. with Square Kilometre Array-low and Hydrogen Epoch of Reionization Array) in the same frequency window. [ABSTRACT FROM AUTHOR]

Recent work has suggested that extreme [O iii] emitting star-forming galaxies are important to reionization. Relatedly, [O iii]/[O ii] has been put forward as an indirect estimator of the Lyman Continuum (LyC) escape fraction (fesc) at z ≳ 4.5 when the opaque IGM renders LyC photons unobservable. Using deep archival U-band (VLT/VIMOS) imaging of a recently confirmed overdensity at z∼ 3.5, we calculate tight constraints on fesc for a sample (N = 73) dominated by extreme [O iii] emitters. We find no LyC signal ( $f_{\rm esc}^{\rm rel} < 6.3^{+0.7}_{-0.7} \hbox{ per cent}$ at 1σ) in a deep U-band stack of our sample (31.98 mag at 1σ). This constraint is in agreement with recent studies of star-forming galaxies spanning z ∼ 1–4 that have found very low average fesc. Despite the galaxies in our study having an estimated average rest-frame EW([O iii]λ5007) ∼ 400 Å and [O iii]/[O ii] ∼ 4 from composite SED fitting, we find no LyC detection, which brings into question the potential of [O iii]/[O  ii] as an effective probe of the LyC – a majority of LyC emitters have [O iii]/[O ii] > 3, but we establish here that [O iii]/[O ii] > 3 does not guarantee significant LyC leakage for a population. Since even extreme star-forming galaxies are unable to produce the $f_{\rm esc}\sim 10{-}15\hbox{ per cent}$ required by most theoretical calculations for star-forming galaxies to drive reionization, there must either be a rapid evolution of fesc between z∼ 3.5 and the epoch of reionization, or hitherto observationally unstudied sources [e.g. ultrafaint low-mass galaxies with log (M/M⊙) ∼ 7–8.5] must make an outsized contribution to reionization. [ABSTRACT FROM AUTHOR]

21 cm cosmology is a promising new probe of the evolution of visible matter in our universe, especially during the poorly constrained Cosmic Dawn and Epoch of Reionization. However, in order to separate the 21 cm signal from bright astrophysical foregrounds, we need an exquisite understanding of our telescopes so as to avoid adding spectral structure to spectrally smooth foregrounds. One powerful calibration method relies on repeated simultaneous measurements of the same interferometric baseline to solve for the sky signal and for instrumental parameters simultaneously. However, certain degrees of freedom are not constrained by asserting internal consistency between redundant measurements. In this paper, we review the origin of these degeneracies of redundant-baseline calibration and demonstrate howthey can source unwanted spectral structure in our measurement and show how to eliminate that additional, artificial structure. We also generalize redundant calibration to dual-polarization instruments, derive the degeneracy structure, and explore the unique challenges to calibration and preserving spectral smoothness presented by a polarized measurement. [ABSTRACT FROM AUTHOR]

The thermal state of the post-reionization IGM is sensitive to the timing of reionization and the nature of the ionizing sources. We have modelled here the thermal state of the IGM in cosmological radiative transfer simulations of a realistic, extended, spatially inhomogeneous hydrogen reionization process, carefully calibrated with Ly α forest data. We compare these with cosmological simulations run using a spatially homogeneous ionizing background. The simulations with a realistic growth of ionized regions and a realistic spread in reionization redshifts show, as expected, significant spatial fluctuations in the temperature--density relation (TDR) of the post-reionization IGM. The most recently ionized regions are hottest and exhibit a flatter TDR. In simulations consistent with the average TDR inferred from Ly α forest data, these spatial fluctuations have a moderate but noticeable effect on the statistical properties of the Ly α opacity of the IGM at z ~ 4-6. This should be taken into account in accurate measurements of the thermal properties of the IGM and the free-streaming of dark matter from Ly α forest data in this redshift range. The spatial variations of the TDR predicted by our simulations are, however, smaller by about a factor of 2 than would be necessary to explain the observed large spatial opacity fluctuations on large (≥50 h-1 comoving Mpc) scales at z ... 5.5. [ABSTRACT FROM AUTHOR]

We extend 21cmmc, a Monte Carlo Markov Chain sampler of 3D reionization simulations, to perform parameter estimation directly on 3D light-cones of the cosmic 21 cm signal. This brings theoretical analysis closer to the tomographic 21 cm observations achievable with next generation interferometers like the Hydrogen Epoch of Reionization Array and the Square Kilometre Array. Parameter recovery can therefore account for modes that evolve with redshift/frequency. Additionally, simulated data can be more easily corrupted to resemble real data. Using the light-cone version of 21cmmc, we quantify the biases in the recovered astrophysical parameters if we use the 21 cm power spectrum from the co-evolution approximation to fit a 3D light-cone mock observation. While ignoring the light-cone effect under most assumptions will not significantly bias the recovered astrophysical parameters, it can lead to an underestimation of the associated uncertainty. However, significant biases (∼few – 10σ) can occur if the 21 cm signal evolves rapidly (i.e. the epochs of reionization and heating overlap significantly), and (i) foreground removal is very efficient, allowing large physical scales ( $k \lesssim 0.1$  Mpc−1) to be used in the analysis or (ii) theoretical modelling is accurate to within ∼10 per cent in the power spectrum amplitude. [ABSTRACT FROM AUTHOR]

Using Shapefinders, which are ratios of Minkowski functionals, we study the morphology of neutral hydrogen (H i) density fields, simulated using seminumerical technique (inside-out), at various stages of reionization. Accompanying the Shapefinders, we also employ the 'largest cluster statistic' (LCS), originally proposed in Klypin & Shandarin, to study the percolation in both neutral and ionized hydrogen. We find that the largest ionized region is percolating below the neutral fraction $x_{{\rm H}\,{{\small I}}}\lesssim 0.728$ (or equivalently z ≲ 9). The study of Shapefinders reveals that the largest ionized region starts to become highly filamentary with non-trivial topology near the percolation transition. During the percolation transition, the first two Shapefinders – 'thickness' (T) and 'breadth' (B) – of the largest ionized region do not vary much, while the third Shapefinder – 'length' (L) – abruptly increases. Consequently, the largest ionized region tends to be highly filamentary and topologically quite complex. The product of the first two Shapefinders, T × B, provides a measure of the 'cross-section' of a filament-like ionized region. We find that, near percolation, the value of T × B for the largest ionized region remains stable at ∼7 Mpc2 (in comoving scale) while its length increases with time. Interestingly, all large ionized regions have similar cross-sections. However, their length shows a power-law dependence on their volume, L ∝ V0.72, at the onset of percolation. [ABSTRACT FROM AUTHOR]

We have developed a modular seminumerical code that computes the time and spatially dependent ionization of neutral hydrogen ( ${\rm H}\,\rm {\small {I}}$ ), neutral ( ${\rm He}\,\rm {\small {I}}$ ), and single-ionized helium ( ${\rm He}\,\rm {\small {II}}$ ) in the intergalactic medium (IGM). The model accounts for recombinations and provides different descriptions for the photoionization rate that are used to calculate the residual ${\rm H}\,\rm {\small {I}}$ fraction in ionized regions. We compare different seminumerical reionization schemes to a radiative transfer (RT) simulation. We use the RT simulation as a benchmark, and find that the seminumerical approaches produce similar ${\rm H}\,\rm {\small {II}}$ and ${\rm He}\,\rm {\small {II}}$ morphologies and power spectra of the ${\rm H}\,\rm {\small {I}}$ 21 cm signal throughout reionization. As we do not track partial ionization of ${\rm He}\,\rm {\small {II}}$ , the extent of the double-ionized helium ( ${\rm He}\,\rm {\small {III}}$ ) regions is consistently smaller. In contrast to previous comparison projects, the ionizing emissivity in our seminumerical scheme is not adjusted to reproduce the redshift evolution of the RT simulation, but directly derived from the RT simulation spectra. Among schemes that identify the ionized regions by the ratio of the number of ionization and absorption events on different spatial smoothing scales, we find those that mark the entire sphere as ionized when the ionization criterion is fulfilled to result in significantly accelerated reionization compared to the RT simulation. Conversely, those that flag only the central cell as ionized yield very similar but slightly delayed redshift evolution of reionization, with up to 20 per cent ionizing photons lost. Despite the overall agreement with the RT simulation, our results suggest that constraining ionizing emissivity-sensitive parameters from seminumerical galaxy formation-reionization models are subject to photon nonconservation. [ABSTRACT FROM AUTHOR]

Observations of the Milky Way (MW), M31, and their vicinity, known as the Local Group (LG), can provide clues about the sources of reionization. We present a suite of radiative transfer simulations based on initial conditions provided by the Constrained Local UniversE Simulations (CLUES) project that are designed to recreate the Local Universe, including a realistic MW-CM31 pair and a nearby Virgo. Our box size (91Mpc) is large enough to incorporate the relevant sources of ionizing photons for the LG. We employ a range of source models, mimicking the potential effects of radiative feedback for dark matter haloes between ~108 and 109M☉. Although the LG mostly reionizes in an inside-out fashion, the final 40 per cent of its ionization shows some outside influence. For the LG satellites, we find no evidence that their redshift of reionization is related to the present-day mass of the satellite or the distance from the central galaxy. We find that fewer than 20 per cent of present-day satellites for MW and M31 have undergone any star formation prior to the end of global reionization. Approximately 5 per cent of these satellites could be classified as fossils, meaning the majority of star formation occurred at these early times. The more massive satellites have more cumulative star formation prior to the end of global reionization, but the scatter is significant, especially at the low-mass end. Present-day mass and distance from the central galaxy are poor predictors for the presence of ancient stellar populations in satellite galaxies. [ABSTRACT FROM AUTHOR]

The survey of Lyman α emitters (LAEs) with the Subaru Hyper Suprime-Cam, called SILVERRUSH (Ouchi et al. 2018, PASJ, 70, S13), is producing massive data of LAEs at z ≳ 6. Here we present LAE simulations to compare the SILVERRUSH data. In 162³ comoving Mpc³ boxes, where numerical radiative transfer calculations of reionization were performed, LAEs have been modeled with physically motivated analytic recipes as a function of halo mass. We have examined 2³ models depending on the presence or absence of dispersion of halo Lyα emissivity, dispersion of the halo Lyα optical depth, τα, and halo mass dependence of τα. The unique free parameter in our model, a pivot value of τα, is calibrated so as to reproduce the z = 5.7 Lyα luminosity function (LF) of SILVERRUSH. We compare our model predictions with Lyα LFs at z = 6.6 and 7.3, LAE angular auto-correlation functions (ACFs) at z = 5.7 and 6.6, and LAE fractions in Lyman break galaxies at 5 < z < 7. The Lyα LFs and ACFs are reproduced by multiple models, but the LAE fraction turns out to be the most critical test. The dispersion of τα and the halo mass dependence of τα are essential to explain all observations reasonably. Therefore, a simple model of one-to-one correspondence between halo mass and Lyα luminosity with a constant Lyα escape fraction has been ruled out. Based on our best model, we present a formula to estimate the intergalactic neutral hydrogen fraction, xHI, from the observed Lyα luminosity density at z ≳ 6. We finally obtain xHI = 0.5-0.3+0.1 as a volume-average at z = 7.3. [ABSTRACT FROM AUTHOR]

In the local Universe, integrated X-ray emission from high-mass X-ray binaries (HMXBs) is dominated by the brightest ultraluminous X-ray sources (ULXs) with luminosity ≳1040 erg s-1. Such rare objects probably also dominated the production of X-rays in the early Universe. We demonstrate that a ULX with LX ~ 1040-1041 erg s-1 (isotropic-equivalent luminosity in the 0.1-10 keV energy band) shining for ~105 yr (the expected duration of a supercritically accreting phase in HMXBs) can significantly ionize the ISM in its host dwarf galaxy of total mass M ~ 107-108 M⊙ and thereby reduce its opacity to soft X-rays. As a result, the fraction of the soft X-ray (below 1 keV) radiation from the ULX escaping into the intergalactic medium (IGM) can increase from ~20-50 per cent to ~30-80 per cent over its lifetime. This implies that HMXBs can induce a stronger heating of the IGM at z ≳ 10 compared to estimates neglecting the ULX feedback on the ISM. However, larger galaxies with M ≳ 3 x 108 M⊙ could not be significantly ionized even by the brightest ULXs in the early Universe. Since such galaxies probably started to dominate the global star formation rate at z ≲ 10, the overall escape fraction of soft X-rays from the HMXB population probably remained low, ≲30 per cent, at these epochs. [ABSTRACT FROM AUTHOR]

Three-dimensional radiative transfer simulations of the epoch of reionization can produce realistic results, but are computationally expensive. On the other hand, simulations relying on one-dimensional radiative transfer solutions are faster but limited in accuracy due to their more approximate nature. Here, we compare the performance of the reionization simulation codes GRIZZLY and C²-RAY which use 1D and 3D radiative transfer schemes, respectively. The comparison is performed using the same cosmological density fields, halo catalogues, and source properties. We find that the ionization maps, as well as the 21-cm signal maps from these two simulations are very similar even for complex scenarios which include thermal feedback on low-mass haloes. The comparison between the schemes in terms of the statistical quantities such as the power spectrum of the brightness temperature fluctuation agrees with each other within 10 per cent error throughout the entire reionization history. GRIZZLY seems to perform slightly better than the seminumerical approaches considered in Majumdar et al. which are based on the excursion set principle. We argue that GRIZZLY can be efficiently used for exploring parameter space, establishing observations strategies, and estimating parameters from 21-cm observations. [ABSTRACT FROM AUTHOR]

Context. Finding the sources responsible for the hydrogen reionization is one of the most pressing issues in observational cosmology. Bright quasi-stellar objects (QSOs) are known to ionize their surrounding neighborhood, but they are too few to ensure the required HI ionizing background. A significant contribution by faint active galactic nuclei (AGNs), however, could solve the problem, as recently advocated on the basis of a relatively large space density of faint active nuclei at z > 4. Aims. This work is part of a long-term project aimed at measuring the Lyman Continuum escape fraction for a large sample of AGNs at z ~ 4 down to an absolute magnitude of M1450 ~ -23. We have carried out an exploratory spectroscopic program to measure the HI ionizing emission of 16 faint AGNs spanning a broad U-I color interval, with I ~ 21-23, and 3:6 < z < 4.2. These AGNs are three magnitudes fainter than the typical SDSS QSOs (M1450 . ≲26) which are known to ionize their surrounding IGM at z ≳ 4. Methods. We acquired deep spectra of these faint AGNs with spectrographs available at the VLT, LBT, and Magellan telescopes, that is, FORS2, MODS1-2, and LDSS3, respectively. The emission in the Lyman Continuum region, close to 900 Å rest frame, has been detected with a signal to noise ratio of ~10-120 for all 16 AGNs. The flux ratio between the 900 Å rest-frame region and 930 Å provides a robust estimate of the escape fraction of HI ionizing photons. Results. We have found that the Lyman Continuum escape fraction is between 44 and 100% for all the observed faint AGNs, with a mean value of 74% at 3:6 < z < 4.2 and -25.1 ≲ M1450 ≲-23.3, in agreement with the value found in the literature for much brighter QSOs (M1450 ≲ -26) at the same redshifts. The Lyman Continuum escape fraction of our faint AGNs does not show any dependence on the absolute luminosities or on the observed U-I colors of the objects. Assuming that the Lyman Continuum escape fraction remains close to ~75% down to M1450 ~ -18, we find that the AGN population can provide between 16 and 73% (depending on the adopted luminosity function) of the whole ionizing UV background at z ~ 4, measured through the Lyman forest. This contribution increases to 25-100% if other determinations of the ionizing UV background are adopted from the recent literature. Conclusions. Extrapolating these results to z ~ 5-7, there are possible indications that bright QSOs and faint AGNs can provide a significant contribution to the reionization of the Universe, if their space density is high at M1450 ~ -23. [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]

Supermassive stars born in pristine environments in the early Universe hold the promise of being the seeds for the supermassive black holes observed as high redshift quasars shortly after the epoch of reionisation. H2 suppression is thought to be crucial in order to negate normal Population III star formation and allow high accretion rates to drive the formation of supermassive stars. Only in the cases where vigorous fragmentation is avoided will amonolithic collapse be successful, giving rise to a singlemassive central object. We investigate the number of fragmentation sites formed in collapsing atomic cooling haloes subject to various levels of background Lyman-Werner flux. The background Lyman-Werner flux manipulates the chemical properties of the gas in the collapsing halo by destroying H2. We find that only when the collapsing gas cloud shifts from the molecular to the atomic cooling regime is the degree of fragmentation suppressed. In our particular case, we find that this occurs above a critical Lyman-Werner background of J ~ 10 J21. The important criterion being the transition to the atomic cooling regime rather than the actual value of J, which will vary locally. Once the temperature of the gas exceeds T ≥ 104 K and the gas transitions to atomic line cooling, then vigorous fragmentation is strongly suppressed. [ABSTRACT FROM AUTHOR]

We report the detection of the Lyman continuum (LyC) radiation of the compact star-forming galaxy (SFG) J1154+2443 observed with the Cosmic Origins Spectrograph (COS) onboard the Hubble Space Telescope. This galaxy, at a redshift of z = 0.3690, is characterized by a high emission-line flux ratio O32 = [O iii] λ5007/[O ii] λ3727 = 11.5. The escape fraction of the LyC radiation fesc(LyC) in this galaxy is 46 per cent, the highest value found so far in low-redshift SFGs and one of the highest values found in galaxies at any redshift. The narrow double-peaked Ly α emission line is detected in the spectrum of J1154+2443 with a separation between the peaks Vsep of 199 km s−1, one of the lowest known for Ly α-emitting galaxies, implying a high fesc(Ly α). Comparing the extinction-corrected Ly α/H β flux ratio with the case B value, we find fesc(Ly α) = 98 per cent. Our observations, combined with previous detections in the literature, reveal an increase of O32 with increasing fesc(LyC). We also find a tight anticorrelation between fesc(LyC) and Vsep. The surface brightness profile derived from the COS acquisition image reveals a bright star-forming region in the centre and an exponential disc in the outskirts with a disc scale length α = 1.09 kpc. J1154+2443, compared to other known low-redshift LyC leakers, is characterized by the lowest metallicity, 12+log O/H = 7.65 ± 0.01, the lowest stellar mass M⋆ = 108.20 M⊙, a similar star formation rate SFR = 18.9 M⊙ yr−1, and a high specific SFR of 1.2 × 10−7 yr−1. [ABSTRACT FROM AUTHOR]

We present a baseline sensitivity analysis of the Hydrogen Epoch of Reionization Array (HERA) and its build-out stages to one-point statistics (variance, skewness, and kurtosis) of redshifted 21 cm intensity fluctuation from the Epoch of Reionization (EoR) based on realistic mock observations. By developing a full-sky 21 cm light-cone model, taking into account the proper field of view and frequency bandwidth, utilizing a realistic measurement scheme, and assuming perfect foreground removal, we show that HERA will be able to recover statistics of the sky model with high sensitivity by averaging over measurements from multiple fields. All build-out stages will be able to detect variance, while skewness and kurtosis should be detectable for HERA128 and larger. We identify sample variance as the limiting constraint of the measurements at the end of reionization. The sensitivity can also be further improved by performing frequency windowing. In addition, we find that strong sample variance fluctuation in the kurtosis measured from an individual field of observation indicates the presence of outlying cold or hot regions in the underlying fluctuations, a feature that can potentially be used as an EoR bubble indicator. [ABSTRACT FROM AUTHOR]

The light-cone (LC) effect causes the Epoch of Reionization (EoR) 21-cm signal Tb(n, v) to evolve significantly along the line-of-sight (LoS) direction v. In the first part of this paper, we present a method to properly incorporate the LC effect in simulations of the EoR 21-cm signal that includes peculiar velocities. Subsequently, we discuss how to quantify the second-order statistics of the EoR 21-cm signal in the presence of the LC effect. We demonstrate that the 3D power spectrum P(k) fails to quantify the entire information because it assumes the signal to be ergodic and periodic, whereas the LC effect breaks these conditions along the LoS. Considering a LC simulation centred at redshift 8 where the mean neutral fraction drops from 0.65 to 0.35 across the box, we find that P(k) misses out ~40 per cent of the information at the two ends of the 17.41MHz simulation bandwidth. The multifrequency angular power spectrum (MAPS) Cl(v1, v2) quantifies the statistical properties of Tb(n, v) without assuming the signal to be ergodic and periodic along the LoS. We expect this to quantify the entire statistical information of the EoR 21-cm signal. We apply MAPS to our LC simulation and present preliminary results for the EoR 21-cm signal. [ABSTRACT FROM AUTHOR]

We use 30 high-resolution dark matter haloes of the Caterpillar simulation suite to probe the first stars and galaxies of MilkyWay-mass systems. We quantify the environment of the high-z progenitors of theMilkyWay and connect them to the properties of the host and satellites today. We identify the formation sites of the first generation of Population III (Pop III) stars (z ~ 25) and first galaxies (z ~ 22) with several different models based on a minimum halo mass. This includes a simple model for radiative feedback, the primary limitation of the model. Through this method we find approximately 23 000 ± 5000 Pop III potentially star-forming sites per MilkyWay-mass host, though this number is drastically reduced to ~550 star-forming sites if feedback is included. The majority of these haloes identified form in isolation (96 per cent at z = 15) and are not subject to external enrichment by neighbouring haloes (median separation ~1 kpc at z = 15), though half merge with a system larger than themselves within 1.5 Gyr. Using particle tagging, we additionally trace the Pop III remnant population to z = 0 and find an order of magnitude scatter in their number density at small (i.e. r < 5 kpc) and large (i.e. r > 50 kpc) galactocentric radii. We provide fitting functions for determining the number of progenitor minihalo and atomic cooling halo systems that present-day satellite galaxies might have accreted since their formation. We determine that observed dwarf galaxies with stellar masses below 104.6M⊙ are unlikely to have merged with any other star-forming systems. [ABSTRACT FROM AUTHOR]

The upcoming SKA1-Low radio interferometer will be sensitive enough to produce tomographic imaging data of the redshifted 21-cm signal from the Epoch of Reionization. Due to the non-Gaussian distribution of the signal, a power spectrum analysis alone will not provide a complete description of its properties. Here, we consider an additional metric which could be derived from tomographic imaging data, namely the bubble size distribution of ionized regions. We study three methods that have previously been used to characterize bubble size distributions in simulation data for the hydrogen ionization fraction - the spherical-average (SPA), mean-free-path (MFP) and friends-of-friends (FOF) methods - and apply them to simulated 21-cm data cubes. Our simulated data cubes have the (sensitivity-dictated) resolution expected for the SKA1-Low reionization experiment and we study the impact of both the light-cone (LC) and redshift space distortion (RSD) effects. To identify ionized regions in the 21-cm data we introduce a new, self-adjusting thresholding approach based on the K-Means algorithm. We find that the fraction of ionized cells identified in this way consistently falls below the mean volume-averaged ionized fraction. From a comparison of the three bubble size methods, we conclude that all three methods are useful, but that theMFP method performs best in terms of tracking the progress of reionization and separating different reionization scenarios. The LC effect is found to affect data spanning more than about 10 MHz in frequency (Δz ~ 0.5). We find that RSDs only marginally affect the bubble size distributions. [ABSTRACT FROM AUTHOR]