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Measurements of the mean free path of Lyman-continuum photons in the intergalactic medium during the epoch of reionization can help constrain the nature of the sources as well as sinks of hydrogen-ionizing radiation. A recent approach to this measurement has been to utilize composite spectra of multiple quasars at |$z\sim 6$|⁠ , and infer the mean free path after correcting the spectra for the presence of quasar proximity zones. This has revealed not only a steep drop in the mean free path from |$z=5$| to |$z=6$|⁠ , but also potentially a mild tension with reionization simulations. We critically examine such direct measurements of the mean free path for biases due to quasar environment, incomplete reionization, and quasar proximity zones. Using cosmological radiative transfer simulations of reionization combined with one-dimensional radiative transfer calculations of quasar proximity zones, we find that the bias in the mean free path due to overdensities around quasars is minimal at |$z\sim 6$|⁠. Patchiness of reionization at this redshift also does not affect the measurements significantly. Fitting our model to the data results in a mean free path of |$\lambda _{\mathrm{mfp}}=1.49^{+0.47}_{-0.52}$|  pMpc at |$z=6$|⁠ , which is consistent with the recent measurements in the literature, indicating robustness with respect to the modelling of quasar proximity zones. We also compare various ways in which the mean free path has been defined in simulations before the end of reionization. Overall, our finding is that recent measurements of the mean free path appear to be robust relative to several sources of potential bias. [ABSTRACT FROM AUTHOR]

Spectra of the highest redshift galaxies taken with JWST are now allowing us to see into the heart of the reionization epoch. Many of these observed galaxies exhibit strong damping wing absorption redward of their Lyman- |$\alpha$| emission. These observations have been used to measure the redshift evolution of the neutral fraction of the intergalactic medium and sizes of ionized bubbles. However, these estimates have been made using a simple analytic model for the intergalactic damping wing. We explore the recent observations with models of inhomogeneous reionization from the Sherwood–Relics simulation suite. We carry out a comparison between the damping wings calculated from the simulations and from the analytic model. We find that although the agreement is good on the red side of the Lyman- |$\alpha$| emission, there is a discrepancy on the blue side due to residual neutral hydrogen present in the simulations, which saturates the intergalactic absorption. For this reason, we find that it is difficult to reproduce the claimed observations of large bubble sizes at |$z \sim 7$|⁠ , which are driven by a detection of transmitted flux blueward of the Lyman- |$\alpha$| emission. We suggest instead that the observations can be explained by a model with smaller ionized bubbles and larger intrinsic Lyman- |$\alpha$| emission from the host galaxy. [ABSTRACT FROM AUTHOR]

Intervening metal absorbers in quasar spectra at z > 6 can be used as probes to study the chemical enrichment of the Universe during the Epoch of Reionization. This work presents the comoving line densities (d n /d X) of low-ionization absorbers, namely, Mg  ii (2796 Å), C  ii (1334 Å), and O   i (1302 Å) across 2 < z < 6 using the E-XQR-30 metal absorber catalogue prepared from 42 XSHOOTER quasar spectra at 5.8 < z < 6.6. Here, we analyse 280 Mg  ii (1.9 < z < 6.4), 22 C  ii (5.2 < z < 6.4), and 10 O  i (5.3 < z < 6.4) intervening absorbers, thereby building up on previous studies with improved sensitivity of 50 per cent completeness at an equivalent width of W > 0.03 Å. For the first time, we present the comoving line densities of 131 weak (W < 0.3 Å) intervening Mg  ii absorbers at 1.9 < z < 6.4 which exhibit constant evolution with redshift similar to medium (0.3 < W < 1.0 Å) absorbers. However, the cosmic mass density of Mg  ii – dominated by strong Mg  ii systems – traces the evolution of global star formation history from redshift 1.9 to 5.5. E-XQR-30 also increases the absorption path-length by a factor of 50 per cent for C  ii and O  i whose line densities show a rising trend towards z > 5, in agreement with previous works. In the context of a decline in the metal enrichment of the Universe at z > 5, the overall evolution in the incidence rates of absorption systems can be explained by a weak – possibly soft fluctuating – ultraviolet background. Our results, thereby, provide evidence for a late reionization continuing to occur in metal-enriched and therefore, biased regions in the Universe. [ABSTRACT FROM AUTHOR]

Spatial variations in the Lyman-α forest opacity at z < 6 seem to require a late end to cosmic reionization. In this picture, the Universe contains neutral hydrogen 'islands' of up to 100 cMpc/ h in extent down to redshifts as low as z ∼ 5.3. This delayed end to reionization also seems to be corroborated by various other observables. An implication of this scenario is that the power spectrum of the cosmological 21-cm signal at z < 6 is enhanced relative to conventional reionization models by orders of magnitude. However, these neutral hydrogen islands are also predicted to be at the locations of the deepest voids in the cosmological large-scale structure. As a result, the distribution of the 21-cm signal from them is highly non-Gaussian. We derive the 21-cm bispectrum signal from these regions using high-dynamic-range radiative transfer simulations of reionization. We find that relative to conventional models in which reionization is complete at z > 6, our model has a significantly larger value of the 21-cm bispectrum. The neutral islands also imprint a feature in the isosceles bispectrum at a characteristic scale of ∼1 cMpc−1. We also study the 21-cm bispectrum for general triangle configuration by defining a triangle index. It should be possible to detect the 21-cm bispectrum signal at ν ≳ 200 MHz using SKA1-LOW for 1080 h of observation, assuming optimistic foreground removal. [ABSTRACT FROM AUTHOR]

Enhanced ionizing radiation in close proximity to redshift z ≳ 6 quasars creates short windows of intergalactic Ly α transmission blueward of the quasar Ly α emission lines. The majority of these Ly α near-zones are consistent with quasars that have optically/UV bright lifetimes of |$t_{\rm Q}\sim 10^{5}\!-\!10^{7}\rm \, yr$|⁠. However, lifetimes as short as |$t_{\rm Q}\lesssim 10^{4}\rm \, yr$| appear to be required by the smallest Ly α near-zones. These short lifetimes present an apparent challenge for the growth of |$\sim 10^{9}\rm \, M_{\odot }$| black holes at z ≳ 6. Accretion over longer time-scales is only possible if black holes grow primarily in an obscured phase, or if the quasars are variable on time-scales comparable to the equilibriation time for ionized hydrogen. Distinguishing between very young quasars and older quasars that have experienced episodic accretion with Ly α absorption alone is challenging, however. We therefore predict the signature of proximate 21-cm absorption around z ≳ 6 radio-loud quasars. For modest pre-heating of intergalactic hydrogen by the X-ray background, where the spin temperature |$T_{\rm S} \lesssim 10^{2}\rm \, K$| prior to any quasar heating, we find proximate 21-cm absorption should be observable in the spectra of radio-loud quasars. The extent of the proximate 21-cm absorption is sensitive to the integrated lifetime of the quasar. Evidence for proximate 21-cm absorption from the diffuse intergalactic medium within |$2\!-\!3\rm \, pMpc$| of a (radio-loud) quasar would be consistent with a short quasar lifetime, |$t_{\rm Q}\lesssim 10^{5}\rm \, yr$|⁠ , and would provide a complementary constraint on models for high-redshift black hole growth. [ABSTRACT FROM AUTHOR]

We examine the column density distribution function (CDDF) and Doppler parameter distribution from hydrodynamical simulations and Cosmic Origins Spectrograph (COS) observations of the Ly α forest at redshift 0 ≤ z ≤ 0.2. Allowing for a factor of two uncertainty in the metagalactic H  |$\, \rm \scriptstyle I \, $| photoionization rate, our hydrodynamical simulations are in good agreement (1–1.5σ) with the shape and amplitude of the observed CDDF at H  |$\, \rm \scriptstyle I \, $| column densities |$10^{13.3}\rm \, cm^{-2}\le N_{\rm H\,{\small I}}\le 10^{14.5}\rm \, cm^{-2}$|⁠. However, the Doppler widths of the simulated lines remain too narrow with respect to the COS data. We argue that invoking AGN feedback does not resolve this discrepancy. We also disfavour enhanced photoheating rates as a potential solution, as this requires an unphysically hard UV background spectrum. If instead appealing to a non-canonical source of heating, an additional specific heat injection of |$u \lesssim 6.9\rm \, eV\, m_{\rm p}^{-1}$| is required at z ≲ 2.5 for gas that has |$N_{\rm H\,{\small I}}\simeq 10^{13.5}\rm \, cm^{-2}$| by z  = 0.1. Alternatively, there may be an unresolved line of sight turbulent velocity component of |$v_{\rm turb}\lesssim 8.5\rm \, km\, s^{-1}(N_{\rm H\,{\small I}}/10^{13.5}\rm \, cm^{-2})^{0.21}$| for the coldest gas in the diffuse IGM. [ABSTRACT FROM AUTHOR]

Our understanding of the intergalactic medium at redshifts z  = 5–6 has improved considerably in the last few years due to the discovery of quasars with z > 6 that enable Lyman-α forest studies at these redshifts. A realization from this has been that hydrogen reionization could end much later than previously thought, so that large 'islands' of cold, neutral hydrogen could exist in the IGM at redshifts z  = 5–6. By using radiative transfer simulations of the IGM, we consider the implications of the presence of these neutral hydrogen islands for the 21-cm power spectrum signal and its potential detection by experiments such as hera, ska, lofar , and mwa. In contrast with previous models of the 21-cm signal, we find that thanks to the late end of reionization the 21-cm power in our simulation continues to be as high as |$\Delta ^2_{21}=10~\mathrm{mK}^2$| at k ∼ 0.1  h  cMpc−1 at z  = 5–6. This value of the power spectrum is several orders of magnitude higher than that in conventional models considered in the literature for these redshifts. Such high values of the 21-cm power spectrum should be detectable by hera and ska1-low in ∼1000 h, assuming optimistic foreground subtraction. This redshift range is also attractive due to relatively low sky temperature and potentially greater abundance of multiwavelength data. [ABSTRACT FROM AUTHOR]

We characterize the thermal state of the intergalactic medium (IGM) in 10 redshift bins in the range 2 ≤ z ≤ 4 with a sample of 103 high-resolution, high S/N  Ly  α forest spectra using four different flux distribution statistics. Our measurements are calibrated with mock spectra from a large suite of hydrodynamical simulations post-processed with our thermal IGM evolution code cite , finely sampling amplitude, and slope of the expected temperature–density relation. The thermal parameters inferred from our measurements of the flux power spectrum, Doppler parameter distribution, as well as wavelet and curvature statistics agree well within their respective errors and all clearly show the peak in temperature and minimum in slope of the temperature density relation expected from  He  ii reionization. Combining our measurements from the different flux statistics gives T 0 = (14 750 ± 1322) K for the peak temperature at mean density and a corresponding minimum slope γ = 1.225 ± 0.120. The peak in the temperature evolution occurs around z ≈ 3, in agreement with previous measurements that had suggested the presence of such a peak, albeit with a large scatter. Using cite , we also calculate the thermal state of the IGM predicted by five widely used (spatially homogeneous) UV-background models. The rather rapid thermal evolution inferred by our measurements is well reproduced by two of the models, if we assume (physically well motivated) non-equilibrium evolution with photoheating rates that are reduced by a moderate factor of ∼0.7–0.8. The other three models predict  He  ii reionization to be more extended with a higher temperature peak occurring somewhat earlier than our measurements suggest. [ABSTRACT FROM AUTHOR]

The Ly α emission line is one of the most promising probes of cosmic reionization but isolating the signature of a change in the ionization state of the intergalactic medium (IGM) is challenging because of intrinsic evolution and internal radiation transfer effects. We present the first study of the evolution of Ly α emitters (LAE) during the epoch of reionization based on a full radiation-hydrodynamics cosmological simulation that is able to capture both the large-scale process of reionization and the small-scale properties of galaxies. We predict the Ly α emission of galaxies in the 103 cMpc3 sphinx  simulation at 6 ≤ z ≤ 9 by computing the full Ly α radiation transfer from interstellar medium (ISM) to IGM scales. sphinx  is able to reproduce many observational constraints such as the UV/Ly α luminosity functions and stellar mass functions at z ≳ 6 for the dynamical range probed by our simulation (M 1500 ≳ −18, LLy α ≲ 1042 erg s−1, M ⋆ ≲ 109 M⊙). As intrinsic Ly α emission and internal Ly α escape fractions barely evolve from z  = 6–9, the observed suppression of Ly α luminosities with increasing redshift is fully attributed to IGM absorption. For most observable galaxies (M 1500 ≲ −16), the Ly α line profiles are slightly shifted to the red due to internal radiative transfer effects that mitigates the effect of IGM absorption. Overall, the enhanced Ly α suppression during reionization traces the IGM neutral fraction |$x_{{\rm H\, {i}}}$| well, but the predicted amplitude of this reduction is a strong function of the Ly α peak shift, which is set at ISM/circumgalactic medium scales. We find that a large number of LAEs could be detectable in very deep surveys during reionization when |$x_{{\rm H\, {i}}}$| is still |$\approx 50{{\ \rm per\ cent}}$|⁠. [ABSTRACT FROM AUTHOR]

Identifying low-redshift galaxies that emit Lyman continuum radiation (LyC leakers) is one of the primary, indirect methods of studying galaxy formation in the epoch of reionization. However, not only has it proved challenging to identify such systems, it also remains uncertain whether the low-redshift LyC leakers are truly 'analogues' of the sources that reionized the Universe. Here, we use high-resolution cosmological radiation hydrodynamics simulations to examine whether simulated galaxies in the epoch of reionization share similar emission line properties to observed LyC leakers at z ∼ 3 and z ∼ 0. We find that the simulated galaxies with high LyC escape fractions (f esc) often exhibit high O32 and populate the same regions of the R23–O32 plane as z ∼ 3 LyC leakers. However, we show that viewing angle, metallicity, and ionization parameter can all impact where a galaxy resides on the O32– f esc plane. Based on emission line diagnostics and how they correlate with f esc, lower metallicity LyC leakers at z ∼ 3 appear to be good analogues of reionization-era galaxies. In contrast, local [S  ii ]-deficient galaxies do not overlap with the simulated high-redshift LyC leakers on the S  ii Baldwin–Phillips–Terlevich (BPT) diagram; however, this diagnostic may still be useful for identifying leakers. We use our simulated galaxies to develop multiple new diagnostics to identify LyC leakers using infrared and nebular emission lines. We show that our model using only [C  ii ]158  μ m and [O  iii ]88  μ m can identify potential leakers from non-leakers from the local Dwarf Galaxy Survey. Finally, we apply this diagnostic to known high-redshift galaxies and find that MACS 1149_JD1 at z  = 9.1 is the most likely galaxy to be actively contributing to the reionization of the Universe. [ABSTRACT FROM AUTHOR]

We compare a sample of five high-resolution, high S/N  Ly α forest spectra of bright 6 < z < ∼6.5 QSOs aimed at spectrally resolving the last remaining transmission spikes at z > 5 with those obtained from mock absorption spectra from the Sherwoodand Sherwood–Relics simulation suites of hydrodynamical simulations of the intergalactic medium (IGM). We use a profile-fitting procedure for the inverted transmitted flux, 1 − F , similar to the widely used Voigt profile fitting of the transmitted flux F at lower redshifts, to characterize the transmission spikes that probe predominately underdense regions of the IGM. We are able to reproduce the width and height distributions of the transmission spikes, both with optically thin simulations of the post-reionization Universe using a homogeneous UV background and full radiative transfer simulations of a late reionization model. We find that the width of the fitted components of the simulated transmission spikes is very sensitive to the instantaneous temperature of the reionized IGM. The internal structures of the spikes are more prominent in low temperature models of the IGM. The width distribution of the observed transmission spikes, which require high spectral resolution (≤ 8  km s−1) to be resolved, is reproduced for optically thin simulations with a temperature at mean density of T 0 = (11 000 ± 1600, 10 500 ± 2100, 12 000 ± 2200) K at z = (5.4, 5.6, 5.8). This is weakly dependent on the slope of the temperature-density relation, which is favoured to be moderately steeper than isothermal. In the inhomogeneous, late reionization, full radiative transfer simulations where islands of neutral hydrogen persist to z ∼ 5.3, the width distribution of the observed transmission spikes is consistent with the range of T 0 caused by spatial fluctuations in the temperature–density relation. [ABSTRACT FROM AUTHOR]

A long (110 cMpc  h−1) and deep absorption trough in the Ly α forest has been observed extending down to redshift 5.5 in the spectrum of ULAS J0148+0600. Although no Ly α transmission is detected, Ly β spikes are present which has led to claims that the gas along this trough must be ionized. Using high-resolution cosmological radiative transfer simulations in large volumes, we show that in a scenario where reionization ends late (z ∼ 5.2), our simulations can reproduce troughs as long as observed. In this model, we find that the troughs are caused by islands of neutral hydrogen. Small ionized holes within the neutral islands allow for the transmission of Ly β. We have also modelled the Ly α emitter population around the simulated troughs, and show that there is a deficit of Ly α emitters close to the trough as is observed. [ABSTRACT FROM AUTHOR]

We study the effect of different feedback prescriptions on the properties of the low-redshift (z ≤ 1.6) Lyα forest using a selection of hydrodynamical simulations drawn from the Sherwood simulation suite. The simulations incorporate stellar feedback, active galactic nuclei (AGN) feedback and a simplified scheme for efficiently modelling the low column density Lyα forest. We confirm a discrepancy remains between Cosmic Origins Spectrograph (COS) observations of the Lyα forest column density distribution function (CDDF) at z ≃ 0.1 for high column density systems (NHI > 1014 cm-2), as well as Lyα velocity widths that are too narrow compared to the COS data. Stellar or AGN feedback-as currently implemented in our simulations-has only a small effect on the CDDF and velocity width distribution. We conclude that resolving the discrepancy between the COS data and simulations requires an increase in the temperature of overdense gas with Δ = 4-40, either through additional He IIphotoheating at z > 2 or fine-tuned feedback that ejects overdense gas into the intergalactic medium at just the right temperature for it to still contribute significantly to the Lyα forest. Alternatively a larger, currently unresolved turbulent component to the line width could resolve the discrepancy. [ABSTRACT FROM AUTHOR]

We compare the low-redshift (z ≃ 0.1) Lyα forest from hydrodynamical simulations with data from the Cosmic Origins Spectrograph. We find the tension between the observed number of lines with b-parameters in the range of 25-45 km s-1 and the predictions from simulations that incorporate either vigorous feedback from active galactic nuclei or that exclude feedback altogether. The gas in these simulations is, respectively, either too hot to contribute to the Lyα absorption or too cold to produce the required linewidths. Matching the observed b-parameter distribution therefore requires feedback processes that thermally or turbulently broaden the absorption features without collisionally (over)ionizing hydrogen. This suggests that the Lyα forest b-parameter distribution is a valuable diagnostic of galactic feedback in the low-redshift Universe. We furthermore confirm that the low-redshift Lyα forest column density distribution is better reproduced by an ultraviolet background with the H I photoionization rate a factor of 1.5-3 higher than predicted by Haardt and Madau. [ABSTRACT FROM AUTHOR]

We present models of low- and high-ionization metal-line absorbers (OI, CII, CIV and Mg II) during the end of the reionization epoch, at z ~ 6. Using four cosmological hydrodynamical simulations with different feedback schemes (including the Illustris and Sherwood simulations) and two different choices of hydro-solver, we investigate how the overall incidence rate and equivalent width distribution of metal-line absorbers varies with the galactic wind prescription. We find that the OI and CII absorbers are reasonably insensitive to the feedback scheme. All models, however, struggle to reproduce the observations of CIV and MgII, which are probing down to lower overdensities than OI and CII at z ~ 6, suggesting that the metals in the simulations are not being transported out into the intergalactic medium efficiently enough. The situation is improved but not resolved if we choose a harder (but still reasonable) and/or (locally) increased UV background at z ~ 6. [ABSTRACT FROM AUTHOR]

We combine high-resolution hydrodynamical simulations with an intermediate resolution, dark matter only simulation and an analytical model for the growth of ionized regions to estimate the large-scale distribution and redshift evolution of the visibility of Lyα emission in 6 ≤ z ≤ 8 galaxies. The inhomogeneous distribution of neutral hydrogen during the reionization process results in significant fluctuations in the Lyα transmissivity on large scales. The transmissivity depends not only on the ionized fraction of the intergalactic medium by volume and the amplitude of the local ionizing background, but is also rather sensitive to the evolution of the relative velocity shift of the Lyα emission line due to resonant scattering. We reproduce a decline in the space density of Lyα emitting galaxies as rapid as observed with a rather rapidly evolving neutral fraction between z = 6-8, and a typical Lyα line velocity offset of 100 km s-1 redward of systemic at z = 6 which decreases towards higher redshift. The new (02/2015) Planck results indicate such a recent end to reionization is no longer disfavoured by constraints from the cosmic microwave background. [ABSTRACT FROM AUTHOR]

Low-ionization metal absorption due to O i has been identified as an important probe of the physical state of the intergalactic/circumgalactic medium at the tail end of reionization. We use here high-resolution hydrodynamic simulations to interpret the incidence rate of O i absorbers at z ∼ 6 as observed by Becker et al. We infer weak O i absorbers (EW ≳ 0.1 Å) to have typical H i column densities in the range of sub-damped Lyman α systems, densities of 80 times the mean baryonic density and metallicities of about 1/500th solar. This is similar to the metallicity inferred at similar overdensities at z ∼ 3, suggesting that the metal enrichment of the circumgalactic medium around low-mass galaxies has already progressed considerably by z ∼ 6. The apparently rapid evolution of the incidence rates for O i absorption over the redshift range 5 ≲ z ≲ 6 mirrors that of self-shielded Lyman-limit systems at lower redshift and is mainly due to the rapid decrease of the metagalactic photoionization rate at z ≳ 5. We predict the incidence rate of O i absorbers to continue to rise rapidly with increasing redshift as the IGM becomes more neutral. If the distribution of metals extends to lower density regions, O i absorbers will allow the metal enrichment of the increasingly neutral filamentary structures of the cosmic web to be probed. [ABSTRACT FROM AUTHOR]

A variety of independent observational studies have now reported a significant decline in the fraction of Lyman-break galaxies which exhibit Lyα emission over the redshift interval z = 6–7. In combination with the strong damping wing extending redward of Lyα in the spectrum of the bright z = 7.085 quasar ULAS 1120+0641, this has strengthened suggestions that the hydrogen in the intergalactic medium (IGM) is still substantially neutral at z ∼ 7. Current theoretical models imply H i fractions as large as 40–90 per cent may be required to explain these data assuming there is no intrinsic evolution in the Lyα emitter population. We propose that such large neutral fractions are not necessary. Based on a hydrodynamical simulation which reproduces the absorption spectra of high-redshift (z ∼ 6–7) quasars, we demonstrate that the opacity of the intervening IGM redward of rest-frame Lyα can rise rapidly in average regions of the Universe simply because of the increasing incidence of absorption systems which are optically thick to Lyman continuum photons as the tail-end of reionization is approached. Our simulations suggest that these data do not require a large change in the IGM neutral fraction by several tens of per cent from z = 6 to 7, but may instead be indicative of the rapid decrease in the typical mean free path for ionizing photons expected during the final stages of reionization. [ABSTRACT FROM AUTHOR]

ABSTRACT We perform an extensive suite of N-body simulations of the matter power spectrum, incorporating massive neutrinos in the range Mν= 0.15-0.6 eV, probing the non-linear regime at scales k < 10 h Mpc−1 at z < 3. We extend the widely used halofit approximation to account for the effect of massive neutrinos on the power spectrum. In the strongly non-linear regime, halofit systematically overpredicts the suppression due to the free streaming of the neutrinos. The maximal discrepancy occurs at k∼ 1 h Mpc−1, and is at the level of 10 per cent of the total suppression. Most published constraints on neutrino masses based on halofit are not affected, as they rely on data probing the matter power spectrum in the linear or mildly non-linear regime. However, predictions for future galaxy, Lyman α forest and weak lensing surveys extending to more non-linear scales will benefit from the improved approximation to the non-linear matter power spectrum we provide. Our approximation reproduces the induced neutrino suppression over the targeted scales and redshifts significantly better. We test its robustness with regard to changing cosmological parameters and a variety of modelling effects. [ABSTRACT FROM AUTHOR]

ABSTRACT We present measurements of the intergalactic medium (IGM) temperature within ∼5 proper Mpc of seven luminous quasars at z ≃ 6. The constraints are obtained from the Doppler widths of Lyα absorption lines in the quasar near zones and build upon our previous measurement for the z = 6.02 quasar SDSS J0818+1722. The expanded data set, combined with an improved treatment of systematic uncertainties, yields an average temperature at the mean density of () at 68 (95) per cent confidence for a flat prior distribution over 3.2 ≤ log ( T0/K) ≤ 4.8. In comparison, temperatures measured from the general IGM at z ≃ 5 are ∼0.3 dex cooler, implying an additional source of heating around these quasars which is not yet present in the general IGM at slightly lower redshift. This heating is most likely due to the recent reionization of He ii in vicinity of these quasars, which have hard and non-thermal ionizing spectra. The elevated temperatures may therefore represent evidence for the earliest stages of He ii reionization in the most biased regions of the high-redshift Universe. The temperature as a function of distance from the quasars is consistent with being constant, log ( T0/K) ≃ 4.2, with no evidence for a line-of-sight thermal proximity effect. However, the limited extent of the quasar near zones prevents the detection of He iii regions larger than ∼5 proper Mpc. Under the assumption that the quasars have reionized the He ii in their vicinity, we infer that the data are consistent with an average optically bright phase of duration in excess of 106.5 yr. These measurements represent the highest redshift IGM temperature constraints to date, and thus provide a valuable data set for confronting models of H i reionization. [ABSTRACT FROM AUTHOR]

ABSTRACT We present observations of a peculiar Lyα-emitting galaxy at redshift z = 3.344, discovered in a deep, blind spectroscopic survey for faint Lyα emitters with the Magellan II telescope in the Hubble Ultra Deep Field. The galaxy exhibits complex Lyα emission, including an extended, asymmetric component that is partially suppressed by damped Lyα absorption, and two spatially elongated, narrow emission features. Archival Hubble Space Telescope Advanced Camera for Surveys imaging shows evidence for tidal disruption of the stellar component. This V = 27 galaxy appears to give us unprecedented insight into two fundamental stages in the formation of structure at high redshift: the inflow of gas into ordinary galaxies, and the escape of ionizing radiation into the intergalactic medium. Neutral hydrogen, falling in partly in the form of a narrow filament, appears to emit fluorescent Lyα photons induced by the stellar ionizing flux escaping from the disturbed galaxy. The in-falling material may represent primary cold accretion or an interaction-triggered inflow. The rate of ionizing photons required by the observed Lyα emission is consistent with the rate of photons produced by the observed stellar population, with roughly 50 per cent of ionizing photons escaping from the immediate galaxy and encountering the in-falling gas. We briefly discuss cooling radiation and large-scale shocks as additional sources for Lyα and ionizing radiation in high-redshift galaxies, but find that stellar radiation is likely to be the dominant source of ionizing photons for most faint galaxies. The observational properties of the galaxy lend support to a picture where galaxy interactions facilitate the escape of both Lyα and ionizing radiation. We argue that galaxies like the present object may be common at high redshift. This galaxy may therefore be a late example of an interacting population of dwarf galaxies that contribute significantly to the reionization of the universe. [ABSTRACT FROM AUTHOR]

We present measurements of the ionizing ultraviolet background (UVB) at using the quasar proximity effect. The 15 quasars in our sample cover the range , enabling the first proximity-effect measurements of the UVB at . The metagalactic hydrogen ionization rate, , was determined by modelling the combined ionization field from the quasar and the UVB in the proximity zone on a pixel-by-pixel basis. The optical depths in the spectra were corrected for the expected effect of the quasar until the mean flux in the proximity region equalled that in the average Lyα forest, and from this we make a measurement of . A number of systematic effects were tested using synthetic spectra. Noise in the flux was found to be the largest source of bias at , while uncertainties in the mean transmitted Lyα flux are responsible for the largest bias at . The impacts of large-scale overdensities and Lyman limit systems on were also investigated, but found to be small at . We find a decline in with redshift, from at to at ( errors). Compared to UVB measurements at lower redshifts, our measurements suggest a drop of a factor of 5 in the H photoionization rate between and 6. The decline of appears to be gradual, and we find no evidence for a sudden change in the UVB at any redshift that would indicate a rapid change in the attenuation length of ionizing photons. Combined with recent measurements of the evolution of the mean free path of ionizing photons, our results imply a decline in the emissivity of ionizing photons by roughly a factor of 2 from to 6, albeit with significant uncertainty due to the measurement errors in both and the mean free path. [ABSTRACT FROM AUTHOR]

ABSTRACT We present new measurements of the temperature of the intergalactic medium (IGM) derived from the Ly α forest over 2.0 ≤ z≤ 4.8. The small-scale structure in the forest of 61 high-resolution quasi-stellar object spectra is quantified using a new statistic, the curvature, and the conversion to temperature calibrated using a suite of hydrodynamic simulations. At each redshift, we focus on obtaining the temperature at an optimal overdensity probed by the Ly α forest, , where the temperature is nearly a one-to-one function of the curvature regardless of the slope of the temperature-density relation. The median 2 σ statistical uncertainty in these measurements is 8 per cent, though there may be comparable systematic errors due to the unknown amount of Jeans smoothing in the IGM. We use our results to infer the temperature at the mean density, T0. Even for a maximally steep temperature-density relation, T0 must increase from ∼8000 K at z≃ 4.4 to ≳12 000 K at z≃ 2.8. This increase is not consistent with the monotonic decline in T0 expected in the absence of He ii reionization. We therefore interpret the observed rise in temperature as evidence of He ii reionization beginning at z≳ 4.4. The evolution of T0 is consistent with an end to He ii reionization at z∼ 3, as suggested by opacity measurements of the He ii Ly α forest, although the redshift at which T0 peaks will depend somewhat on the evolution of the temperature-density relation. These new temperature measurements suggest that the heat input due to the reionization of He ii dominates the thermal balance of the IGM over an extended period with Δ z≳ 1. [ABSTRACT FROM AUTHOR]

The thermal state of the intergalactic medium (IGM) provides an indirect probe of both the H i and He ii reionization epochs. Current constraints on the IGM temperature from the Lyα forest are restricted to the redshift range , limiting the ability to probe the thermal memory of H i reionization towards higher redshift. In this work, we present the first direct measurement of the IGM temperature around a quasar by analyzing the Doppler widths of Lyα absorption lines in the proximity zone of SDSS J 1722. We use a high-resolution Keck/HIRES spectrum in combination with detailed numerical modelling to obtain the temperature at mean density, ) at 68 (95) per cent confidence assuming a prior probability following H i and He ii reionization. This enables us to place an upper limit on the redshift of H i reionization, zH, within 33 comoving Mpc of SDSS J 1722. If the quasar reionizes the He ii in its vicinity, then in the limit of instantaneous reionization we infer at 68 (95) per cent confidence assuming photoheating is the dominant heat source and that H i reionization is driven by ionizing sources with soft spectra, typical of Population II stars. If the H i and He ii in the IGM around SDSS J 1722 are instead reionized simultaneously by a population of massive metal-free stars, characterized by very hard ionizing spectra, we obtain a tighter upper limit of . Initiating reionization at higher redshifts produces temperatures which are too low with respect to our constraint unless the H i ionizing sources or the quasar itself has spectra significantly harder than typically assumed. [ABSTRACT FROM AUTHOR]

The recently discovered population of ultra-faint extended line emitters, with fluxes of a few times at , can account for the majority of the incidence rate of damped Lyα systems (DLAs) at this redshift if the line emission is interpreted as Lyα. We show here that a model similar to that proposed by Haehnelt, Steinmetz & Rauch (2000) , which reproduces the incidence rate and kinematics of DLAs in the context of Λ cold dark matter models for structure formation, also reproduces the size distribution of the new population of faint Lyα emitters for plausible parameters. This lends further support to the interpretation of the emission as Lyα, as well as the identification of the emitters with the hitherto elusive population of DLA host galaxies. The observed incidence rate of DLAs together with the observed space density and size distribution of the emitters suggest a duty cycle of for the Lyα emission from DLA host galaxies. We further show that Lyα cooling is expected to contribute little to the Lyα emission for the majority of emitters. This leaves centrally concentrated star formation at a rate of a few tenths , surrounded by extended Lyα haloes with radii up to 30–50 kpc, as the most plausible explanation for the origin of the emission. Both the luminosity function of Lyα emission and the velocity width distribution of low ionization absorption require that galaxies inside dark matter (DM) haloes with virial velocities contribute little to the incidence rate of DLAs at , suggesting that energy and momentum input due to star formation efficiently removes gas from these haloes. Galaxies with DM haloes with virial velocities of appear to account for the majority of DLA host galaxies. DLA host galaxies at should thus become the building blocks of typical present-day galaxies like our Milky Way. [ABSTRACT FROM AUTHOR]

The next generation of X-ray telescopes have the potential to detect faint quasars at very high redshift and probe the early growth of massive black holes (BHs). We present modelling of the evolution of the optical and X-ray active galactic nucleus (AGN) luminosity function at based on a cold dark matter (CDM) merger-driven model for the triggering of nuclear activity combined with a variety of fading laws. We extrapolate the merger-driven models to for a range of BH growth scenarios. We predict significant numbers of sources at with fluxes just an order of magnitude below the current detection limits and thus detectable with XEUS and Constellation-X, relatively independently of the fading law chosen. The predicted number of sources at even higher redshift depends sensitively on the early growth history of BHs. For passive evolution models in which BHs grow constantly at their Eddington limit, detectable BHs may be rare beyond even with Generation-X. However, in the more probable scenario that BH growth at can be described by passive evolution with a small duty cycle, or by our merger-driven accretion model, then we predict that XEUS and Generation-X will detect significant numbers of BHs out to and perhaps beyond. [ABSTRACT FROM AUTHOR]

Absorption spectra of high-redshift quasars exhibit an increasingly thick Lyα forest, suggesting that the fraction of neutral hydrogen in the intergalactic medium (IGM) is increasing towards z∼ 6. However, the interpretation of these spectra is complicated by the fact that the Lyα optical depth is already large for neutral hydrogen fractions in excess of 10−4, and also because quasars are expected to reside in dense regions of the IGM. We present a model for the evolution of the ionization state of the IGM which is applicable to the dense, biased regions around high-redshift quasars as well as more typical regions in the IGM. We employ a cold dark matter based model in which the ionizing photons for reionization are produced by star formation in dark matter haloes spanning a wide range of masses, combined with numerical radiative transfer simulations which model the resulting opacity distribution in quasar absorption spectra. With an appropriate choice for the parameter which controls the star formation efficiency, our model is able to simultaneously reproduce the observed Lyα forest opacity at 4 < z < 6, the ionizing photon mean-free-path at z∼ 4 and the rapid evolution of highly ionized near-zone sizes around high-redshift quasars at 5.8 < z < 6.4. In our model, reionization extends over a wide redshift range, starting at z≳ 10 and completing as H ii regions overlap at z∼ 6–7. We find that within 5 physical Mpc of a high-redshift quasar, the evolution of the ionization state of the IGM precedes that in more typical regions by around 0.3 redshift units. More importantly, when combined with the rapid increase in the ionizing photon mean-free-path expected shortly after overlap, this offset results in an ionizing background near the quasar which exceeds the value in the rest of the IGM by a factor of ∼2–3. We further find that in the post-overlap phase of reionization the size of the observed quasar near-zones is not directly sensitive to the neutral hydrogen fraction of the IGM. Instead, these sizes probe the level of the background ionization rate and the temperature of the surrounding IGM. The observed rapid evolution of the quasar near-zone sizes at 5.8 < z < 6.4 can thus be explained by the rapid evolution of the ionizing background, which in our model is caused by the completion of overlap at the end of reionization by 6 ≲ z≲ 7. [ABSTRACT FROM AUTHOR]

H ii regions surrounding supermassive black holes (SMBHs) in an otherwise still neutral intergalactic medium (IGM) are likely to be the most easily detectable sources by future 21-cm experiments like LOFAR. We have made predictions for the size distribution of such H ii regions for several physically motivated models for BH growth at high redshift and compared this to the expected LOFAR sensitivity to these sources. The number of potentially detectable H ii regions does not only depend on the ionization state of the IGM and the decoupling of the spin temperature of the neutral hydrogen from the cosmic microwave background temperature, but is also strongly sensitive to the rate of growth of BHs at high redshift. If the SMBHs at redshift 6 were built up via continuous Eddington-limited accretion from low mass seed BHs at high redshift, then LOFAR is not expected to detect isolated QSO H ii regions at redshifts much larger than 6, and only if the IGM is still significantly neutral. If the high-redshift growth of BHs starts with massive seed BHs and is driven by short-lived accretion events following the merging of BH hosting galaxies then the detection of H ii regions surrounding SMBHs may extend to redshifts as large as 8–9 but is still very sensitive to the redshift to which the IGM remains significantly neutral. The most optimistic predictions are for a model where the SMBHs at z > 6 have grown slowly. H ii regions around SMBHs may then be detected to significantly larger redshifts. [ABSTRACT FROM AUTHOR]

We implement the hydrodynamic particle-mesh (HPM) technique in the hydrodynamical simulation codegadget-2 and quantify the differences between this approximate method and full hydrodynamical simulations of the Lyman α forest in a concordance ΛCDM (cold dark matter) model. At redshifts and 4, the differences between the gas and dark matter distributions, as measured by the one-point distribution of density fluctuations, the density power spectrum and the flux power spectrum, systematically decrease with increasing resolution of the HPM simulation. However, reducing these differences to less than a few per cent requires a significantly larger number of grid cells than particles, with a correspondingly larger demand for memory. Significant differences in the flux decrement distribution remain even for very high-resolution HPM simulations, particularly at low redshift. At , the differences between the flux power spectra obtained from HPM simulations and full hydrodynamical simulations are generally large and of the order of 20–30 per cent, and do not decrease with increasing resolution of the HPM simulation. This is due to the presence of large amounts of shock-heated gas, a situation which is not adequately modelled by the HPM approximation. We confirm the results of Gnedin & Hui that the statistical properties of the flux distribution are discrepant by ≳5–20 per cent when compared to full hydrodynamical simulations. The discrepancies in the flux power spectrum are strongly scale- and redshift-dependent and extend to large scales. Considerable caution is needed in attempts to use calibrated HPM simulations for quantitative predictions of the flux power spectrum and other statistical properties of the Lyman α forest. [ABSTRACT FROM AUTHOR]

Artificial absorption spectra are used to test a variety of instrumental and physical effects on the pixel correlation technique for the detection of weak O vi absorption. At H i optical depths ≲0.3–1, the apparent O vi detections are spurious coincidences due to H i absorption at other redshifts. In this range, the apparent O vi optical depth is independent of H i optical depth. At larger H i optical depths, the apparent O vi optical depth and H i optical depth are correlated. Detailed modelling is required in order to interpret the significance of this relation. High-resolution spectra of four quasi-stellar objects together with a large suite of synthetic spectra are used to show that the detection of O vi in individual spectra is only statistically significant for overdensities ≳5. These overdensities are larger than would be naively inferred from the onset of the correlation and a tight optical depth–density relation. The lower limit for the volume filling factor of regions which are enriched by O vi is 4 per cent at 95 per cent confidence. This is no larger than the observed volume filling factor of the winds from Lyman break galaxies. Previous claims that the observed O vi absorption extends to underdense regions and requires a universal metal enrichment with large volume filling factor, as may be expected from Population III star formation at very high redshift, appear not to be warranted. [ABSTRACT FROM AUTHOR]

Recent work has demonstrated that there is a tight correlation between the mass of a black hole and the velocity dispersion of the bulge of its host galaxy. We show that the model of Kauffmann & Haehnelt, in which bulges and supermassive black holes both form during major mergers, produces a correlation between M[sub bh] and σ with a slope and scatter comparable to the observed relation. In the model the M[sub bh]–σ relation is significantly tighter than the correlation between black hole mass and bulge luminosity, or the correlation between bulge luminosity and velocity dispersion. There are two reasons for this: (i) the gas masses of bulge progenitors depend on the velocity dispersion but not on the formation epoch of the bulge, whereas the stellar masses of the progenitors depend on both; (ii) mergers between galaxies move black holes along the observed M[sub bh]–σ relation, even at late times when the galaxies are gas-poor and black holes grow mainly the by merging of pre-existing black holes. We conclude that the small scatter in the observed M[sub bh]–σ relation is consistent with a picture in which bulges and black holes form over a wide range in redshift. [ABSTRACT FROM AUTHOR]

We demonstrate that the Lyα emission in the absorption troughs of a large sample of stacked damped Lyα absorption systems (DLAS) presented by Rahmani et al. is consistent with the spectral profiles and luminosities of a recently detected population of faint Lyα emitters at . This result supports the suggestion that the faint emitters are to be identified with the host galaxies of DLAS at these redshifts. [ABSTRACT FROM AUTHOR]

Observations of the emission from spatially extended cold gas around bright high-redshift quasars (QSOs) reveal surprisingly large velocity widths exceeding 2000 km s− 1, out to projected distances as large as 30 kpc. The high-velocity widths have been interpreted as the signature of powerful AGN-driven outflows. Naively, these findings appear in tension with hydrodynamic models in which AGN-driven outflows are energy-driven and thus very hot with typical temperatures T ≳ 106-7 K. Using the moving-mesh code arepo, we perform ‘zoom-in’ cosmological simulations of a z ∼ 6 QSO and its environment, following black hole growth and feedback via energy-driven outflows. In the simulations, the QSO host galaxy is surrounded by a clumpy circumgalactic medium pre-enriched with metals due to supernovae-driven galactic outflows. As a result, part of the AGN-driven hot outflowing gas can cool radiatively, leading to large amounts ( ≳ 109 M⊙) of cold gas comoving with the hot bipolar outflow. This results in velocity widths of spatially extended cold gas similar to those observed. We caution, however, that gas inflows, random motions in the deep potential well of the QSO host galaxy and cooling of supernovae-driven winds contribute significantly to the large velocity width of the cold gas in the simulations, complicating the interpretation of observational data. [ABSTRACT FROM PUBLISHER]

Attempts of Magain et al. to detect the host galaxy of the bright quasi-stellar object (QSO) HE0450–2958 have not been successful. We suggest that the supermassive black hole (SMBH) powering the QSO was ejected from the observed ultraluminous infrared galaxy (ULIRG) at the same redshift and at 1.5 arcsec distance. Ejection could have been caused either by recoil due to gravitational wave emission from a coalescing binary of SMBHs or the gravitational slingshot of three or more SMBHs in the ongoing merger of galaxies which triggered the starburst activity in the ULIRG. We discuss implications for the possible hierarchical build-up of SMBHs from intermediate and/or stellar mass black holes, and for the detection of coalescing supermassive binary black holes by LISA. [ABSTRACT FROM AUTHOR]

In a recent paper Pelló et al. have reported a candidate galaxy, A1835–1916, which was found in a near-infrared survey of the central regions of the gravitational lensing cluster A1835. If this detection is confirmed and the detection rate turns out to be typical, then the volume-averaged ultraviolet emissivity must be rising rapidly with increasing redshift. For a magnification resulting from gravitational lensing by a factor estimated by Pelló et al., the inferred star formation rate at would be about one order of magnitude higher than estimates of the star formation rate density at . Objects at would contribute substantially to the total source counts at 1.6 μm and the estimated space density of sources may exceed the space density of dark matter haloes in a ΛCDM model. We therefore argue that if A1835–1916 is indeed at then either the magnification factor may have been overestimated or the galaxy has a top-heavy initial mass function. Sources with the UV flux and space density of A1835–1916 produce hydrogen ionizing photons per hydrogen atom per Hubble time, where fesc is the escape fraction of ionizing photons. This rate should be sufficient to reionize most of the diffuse hydrogen in the Universe at redshift 10. We further use a correlation between the equivalent width and the redshift of the Lyα emission line with respect to the systemic redshift observed in Lyman-break galaxies to obtain constraints on the ionization state of the surrounding intergalactic medium (IGM) from the Gunn–Peterson absorption. These constraints also argue in favour of the surrounding IGM being fully ionized. Pelló et al. may thus have detected a population of sources, which is responsible for the large electron scattering optical depth indicated by the cross-power spectrum of the temperature and polarization fluctuations of the cosmic microwave background as measured by WMAP. [ABSTRACT FROM AUTHOR]