We discuss the possible origin of the double-peaked profiles recently observed in Lyman-Alpha Emitters (LAEs) at the epoch of reionization ($z \gtrsim 6.5$) from obscured active galactic nuclei (AGN). Combining the extent of the Lyman-$α$ near-zones estimated from the blue peak velocity offset in these galaxies, with the ionizing emissivity of quasars at $z \gtrsim 6$, we forecast the intrinsic UV and X-ray luminosities of the AGN needed to give rise to their double-peaked profiles. We also estimate the extent of the obscuration of the AGN by comparing their luminosities to those of similar quasar samples at these epochs. Future X-ray and radio observations, as well as those with the ${James \ Webb \ Space \ Telescope}$, will be valuable tools to test the AGN contribution to the intergalactic-scale ionization zones of high-redshift LAEs.
We present an analysis of the evolution of the Lyman-series forest into the epoch of reionization using cosmological radiative transfer simulations in a scenario where reionization ends late. We explore models with different midpoints of reionization and gas temperatures. We find that once the simulations have been calibrated to match the mean flux of the observed Lyman-$α$ forest at $4 < z < 6$, they also naturally reproduce the distribution of effective optical depths of the Lyman-$β$ forest in this redshift range. We note that the tail of the largest optical depths that is most challenging …
The inhomogeneous cosmological reionization process leaves tangible imprints in the intergalactic medium down to z=4-5. The Lyman-alpha forest flux power spectrum provides a potentially powerful probe of the epoch of reionization. With the existing SDSS I/II quasar sample we show that two cosmological reionization scenarios, one completing reionization at z=6 and the other at z=9, can be distinguished at ~7 sigma level by utilizing Lyman alpha forest absorption spectra at z=4.5+-0.5, in the absence of other physical processes that may also affect the Lyman alpha flux power spectrum. The redshi…
Recent observations of the Lyman-alpha forest show large-scale spatial variations in the intergalactic Lyman-alpha opacity that grow rapidly with redshift at z>5, far in excess of expectations from empirically motivated models. Previous studies have attempted to explain this excess with spatial fluctuations in the ionizing background, but found that this required either extremely rare sources or problematically low values for the mean free path of ionizing photons. Here we report that much -- or potentially all -- of the observed excess likely arises from residual spatial variations in tempera…
The fraction of ionizing photons escaping from galaxies, $f_{esc}$, is at the same time a crucial parameter in modelling reionization and a very poorly known quantity, especially at high redshift. Recent observations are starting to constrain the values of $f_{esc}$ in low-z star-forming galaxies, but the validity of this comparison remains to be verified. Applying at high-z the empirical relation between $f_{esc}$ and the UV slope trends derived from the Low-z Lyman Continuum Survey, we use the DELPHI semi-analytical galaxy formation model to estimate the global ionizing emissivity of high-z …
Neutral diffuse intergalactic gas that existed during the Epoch of Reionization (EoR) suppresses Lyman Alpha (Lya) flux emitted by background galaxies. In this chapter I summarise the increasing observational support for the claim that Lya photons emitted by galaxies at z>6 are suppressed by intervening HI gas. I describe key physical processes that affect Lya transfer during the EoR. I argue that in spite of the uncertainties associated with this complex multiscale problem, the data on Lya emitting galaxies at z=0-6 strongly suggests that the observed reduction in Lya flux from galaxies at z>…
We present here 21 cm predictions from high dynamic range simulations for a range of reionization histories that have been tested against available Lyman-alpha and CMB data. We assess the observability of the predicted spatial 21 cm fluctuations by ongoing and upcoming experiments in the late stages of reionization in the limit in which the hydrogen spin temperature is significantly larger than the CMB temperature. Models consistent with the available Lyman-alpha data and CMB measurement of the Thomson optical depth predict typical values of 10--20 mK^2 for the variance of the 21 cm brightness…
The epoch of reionization (6 < z < 10) marks the period in our universe when the first large galaxies grew to fruition, and began to affect the universe around them. Massive stars, and potentially accreting supermassive black holes, filled the universe with ionizing radiation, burning off the haze of neutral gas that had filled the intergalactic medium (IGM) since recombination (z~1000). The evolution of this process constrains key properties of these earliest luminous sources, thus observationally constraining reionization is a key science goal for the next decade. The measurement of Lyman-al…
Stacking 21-cm Maps around Lyman-$α$ Emitters during Reionization: Prospects for a Cross-correlation Detection with the Hydrogen Epoch of Reionization Array
We present the first results from the ongoing LAGER project (Lyman Alpha Galaxies in the Epoch of Reionization), which is the largest narrowband survey for $z \sim$ 7 galaxies to date. Using a specially built narrowband filter NB964 for the superb large-area Dark-Energy Camera (DECam) on the NOAO/CTIO 4m Blanco telescope, LAGER has collected 34 hours NB964 narrowband imaging data in the 3 deg$^2$ COSMOS field. We have identified 23 Lyman Alpha Emitter (LAE) candidates at $z$ = 6.9 in the central 2-deg$^2$ region, where DECam and public COSMOS multi-band images exist. The resulting luminosity f…
The observed deficit of strongly Lyman-alpha emitting galaxies at z>6.5 is attributed to either increasing neutral hydrogen in the intergalactic medium (IGM) and/or to the evolving galaxy properties. To investigate this, we have performed very deep near-IR spectroscopy of z>7 galaxies using MOSFIRE on the Keck-I Telescope. We measure the Lyman-alpha fraction at z~8 (combined photometric redshift peak at z=7.7) using two methods. First, we derived NLyα/Ntot directly using extensive simulations to correct for incompleteness. Second, we used a Bayesian formalism (introduced by Treu et al. 2012) t…
A number of independent observations suggest that the intergalactic medium was significantly neutral at $z=7$ and that reionization was, perhaps, still in progress at $z=5.7$. The narrowband survey, SILVERRUSH, has mapped over $2,000$ Lyman-$α$ emitters (LAEs) at these redshifts. Previous analyses have assumed that reionization was over by $z=5.7$, but this data may actually sample the final stages of reionization when the last neutral islands were relegated to the cosmic voids. Motivated by these developments, we reexamine LAE void and peak statistics and their ability to constrain reionizati…
The latest measurements of CMB electron scattering optical depth reported by Planck significantly reduces the allowed space of HI reionization models, pointing toward a later ending and/or less extended phase transition than previously believed. Reionization impulsively heats the intergalactic medium (IGM) to $\sim10^4$ K, and owing to long cooling and dynamical times in the diffuse gas, comparable to the Hubble time, memory of reionization heating is retained. Therefore, a late ending reionization has significant implications for the structure of the $z\sim5-6$ Lyman-$α$ (ly$α$) forest. Using…
The Epoch of Reionization (EoR) represents a milestone in the evolution of our Universe. Star-forming galaxies that existed during the EoR likely emitted a significant fraction (~5-40%) of their bolometric luminosity as Lyman Alpha (Lya) line emission. However, neutral intergalactic gas that existed during the EoR was opaque to Lya emission that escaped from galaxies during this epoch, which makes it difficult to observe. The neutral intergalactic medium (IGM) may thus reveal itself by suppressing the Lya flux from background galaxies. Interestingly, a `sudden' reduction in the observed Lya fl…
We investigate Lyman-$α$ transmission spikes at $z > 5$ in synthetic quasar spectra, and discuss their connection to the properties of the intergalactic medium and their ability to constrain reionization models. We use state-of-the-art radiation-hydrodynamic simulations from the Cosmic Reionization On Computers series to predict the number of transmission spikes as a function of redshift, both in the ideal case of infinite spectral resolution and in a realistic observational setting. Transmission spikes are produced in highly-ionized underdense regions located in the vicinity of UV sources. We…
We probe what constraints for the global ionized hydrogen fraction the Void Probability Function (VPF) clustering can give for the Lyman-Alpha Galaxies in the Epoch of Reionization (LAGER) narrowband survey as a function of area. Neutral hydrogen acts like a fog for Lyman-alpha emission, and measuring the drop in the luminosity function of Lyman-$α$ emitters (LAEs) has been used to constrain the ionization fraction in narrowband surveys. However, the clustering of LAEs is independent from the luminosity function's inherent evolution, and can offer additional constraints for reionization under …
We model the high redshift (z > 5) Lyman-$α$ emitting (LAE) galaxy population using the empirical rest-frame equivalent width distribution. We calibrate to the observed luminosity function and angular correlation function at z = 5.7 as measured by the SILVERRUSH survey. This allows us to populate the high-dynamic-range Sherwood simulation suite with LAEs, and to calculate the transmission of their Ly $α$ emission through the inter-galactic medium (IGM). We use this simulated population to explore the effect of the IGM on high-redshift observations of LAEs, and make predictions for the narrowba…
Reionization leads to large spatial fluctuations in the intergalactic temperature that can persist well after its completion. We study the imprints of such fluctuations on the $z\sim5$ Ly$α$ forest flux power spectrum using a set of radiation-hydrodynamic simulations that model different reionization scenarios. We find that large-scale coherent temperature fluctuations bring $\sim20-60\%$ extra power at $k\sim0.002$ s/km, with the largest enhancements in the models where reionization is extended or ends the latest. On smaller scales ($k\gtrsim0.1$ s/km), we find that temperature fluctuations s…
Double-Peaked Ly$α$ Emission during Reionization Requires Nearby Voids and a Favorable Local Ionizing Background
Institute for Basic Science（韩国基础科学研究院）；Center for Computational Sciences（计算科学中心）；The University of Texas at Dallas（德克萨斯大学达拉斯分校）；Chungbuk National University（忠北国立大学）；Observatoire Astronomique de Strasbourg, Université de Strasbourg, CNRS UMR 7550（斯特拉斯堡天文台，斯特拉斯堡大学，法国国家科学研究中心）；Institut d’Astrophysique de Paris, UMR 7095, CNRS, UPMC Univ. Paris VI（巴黎天体物理学研究所，法国国家科学研究中心，巴黎第六大学）；The University of Nottingham（诺丁汉大学）；University of Texas, Austin（德克萨斯大学奥斯汀分校）；University of Sussex（萨塞克斯大学）
We present the first simulations of the high-redshift Ly$α$ intensity field that account for scattering in the intergalactic medium (IGM). Using a 3D Monte Carlo radiative transfer code, we find that Ly$α$ scattering smooths spatial fluctuations in the Ly$α$ intensity on small scales and that the spatial dependence of this smoothing depends strongly on the mean neutral fraction of the IGM. Our simulations find a strong effect of reionization on $k=0.1-1~{\rm Mpc^{-1}}$, with $P_{\rm Lyα}\propto k^{-1.75}$ for $\bar{x}_{\rm HI} = 0.63$ and $P_{\rm Lyα} \propto k^{-2.2}$ for $\bar{x}_{\rm HI} = …
Galaxy Proximate Damped Lyman-Alpha Systems and HI Reionization Topology in TECHNICOLOR DAWN
New Mexico State University（新墨西哥州立大学）；Cosmic Dawn Center (DAWN)（宇宙黎明中心（DAWN））；Niels Bohr Institute, University of Copenhagen / DTU-Space Technical University of Denmark（哥本哈根大学尼尔斯·玻尔研究所/丹麦技术大学空间研究所）
The high redshift Lyman-alpha forest, in particular the Gunn-Peterson trough, is the most unambiguous signature of the neutral to ionized transition of the intergalactic medium (IGM) taking place during the Epoch of Reionization (EoR). Recent studies, e.g. Kulkarni et al. (2019a) and Keating et al. (2019), showed that reproducing the observed Lyman-alpha opacities after overlap required a non-monotonous evolution of cosmic emissivity: rising, peaking at z=6, and then decreasing onwards to z=4. Such an evolution is puzzling considering galaxy build-up and the cosmic star formation rate are stil…
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 $z\sim3…
The time frame in which hydrogen reionization occurred is highly uncertain, but can be constrained by observations of Lyman-alpha (Ly$α$) emission from distant sources. Neutral hydrogen in the intergalactic medium (IGM) attenuates Ly$α$~photons emitted by galaxies. As reionization progressed the IGM opacity decreased, increasing Ly$α$~visibility. The galaxy Ly$α$~luminosity function (LF) is thus a useful tool to constrain the timeline of reionization. In this work, we model the Ly$α$~LF as a function of redshift, $z=5-10$, and average IGM neutral hydrogen fraction, $\overline{x}_\textsc{hi}$. …
The visibility of high-redshift Lyman-alpha emitting galaxies (LAEs) provides important constraints on galaxy formation processes and the Epoch of Reionization (EoR). However, predicting realistic and representative statistics for comparison with observations represents a significant challenge in the context of large-volume cosmological simulations. The THESAN project offers a unique framework for addressing such limitations by combining state-of-the-art galaxy formation (IllustrisTNG) and dust models with the Arepo-RT radiation-magneto-hydrodynamics solver. In this initial study we present Ly…
We report the discovery of a double-peaked Lyman-alpha profile in a galaxy at $z=6.803$, A370p\_z1, in the parallel Frontier Field of Abell 370. The velocity separation between the blue and red peaks of the Lyman-$α$ profile ($Δv=101_{-19}^{+38} (\pm48)\,\text{km s}^{-1}$) suggests an extremely high escape fraction of ionising photons $> 59(51)\% (2σ)$. The spectral energy distribution indicates a young ($50$ Myr), star-forming ($12\pm 6 \, \rm{M}_\odot \rm{yr}^{-1}$) galaxy with an IRAC excess implying strong [OIII]+H$β$ emission. On the basis of the high escape fraction measured, we demonstr…
We present the Technicolor Dawn simulations, a suite of cosmological radiation-hydrodynamic simulations of the first 1.2 billion years. By modeling a spatially-inhomogeneous UVB on-the-fly with 24 frequencies and resolving dark matter halos down to $10^8 M_\odot$ within 12 $h^{-1}$ Mpc volumes, our simulations unify observations of the intergalactic and circumgalactic media, galaxies, and reionization into a common framework. The only empirically-tuned parameter, the fraction $f_{\mathrm{esc,gal}}(z)$ of ionizing photons that escape the interstellar medium, is adjusted to match observations of…
We investigate the cross-correlation between the spatial distribution of Lyman Break Galaxies (LBGs) and the 21cm intensity mapping signal at $z\sim[3-5]$. At these redshifts, galactic feedback is supposed to only marginally affect the matter power spectrum, and the neutral hydrogen distribution is independently constrained by quasar spectra. Using a high resolution N-body simulation, populated with neutral hydrogen a posteriori, we forecast for the expected LBG-21cm cross-spectrum and its error for a 21cm field observed by the Square Kilometre Array (SKA1-LOW and SKA1-MID), combined with a sp…
We present new results from the widest narrow band survey search for Lyman-alpha (Lya) emitters at z=5.7, just after reionization. We survey a total of 7 deg$^2$ spread over the COSMOS, UDS and SA22 fields. We find over 11,000 line emitters, out of which 514 are robust Lya candidates at z=5.7 within a volume of 6.3x10$^6$ Mpc$^3$. Our Lya emitters span a wide range in Lya luminosities, from faint to bright (L$_{\rm Lyα}\sim10^{42.5-44}$ erg s$^{-1}$) and rest-frame equivalent widths (EW$_0$~25-1000 Å) in a single, homogeneous data-set. By combining all our fields we find that the faint end slo…
Using four different suites of cosmological simulations, we generate synthetic spectra for galaxies with different Lyman continuum escape fractions (fesc) at redshifts z=7-9, in the rest-frame wavelength range relevant for the James Webb Space Telescope (JWST) NIRSpec instrument. By investigating the effects of realistic star formation histories and metallicity distributions on the EW(Hb)-beta diagram (previously proposed as a tool for identifying galaxies with very high fesc), we find that neither of these effects are likely to jeopardize the identification of galaxies with extreme Lyman cont…
We calculate Lyman Alpha Emitter (LAE) angular correlation functions (ACFs) at $z \simeq 6.6$ and the fraction of lifetime (for the 100 Myrs preceding $z\simeq6.6$) galaxies spend as Lyman Break Galaxies (LBGs) or as LBGs with Lyman Alpha (Ly$α$) emission using a model that combines SPH cosmological simulations (GADGET-2), dust attenuation and a radiative transfer code (pCRASH). The ACFs are a powerful tool that significantly narrows the 3D parameter space allowed by LAE Ly$α$ and UV luminosity functions (LFs) alone. With this work, we simultaneously constrain the escape fraction of ionizing p…
The visibility of LyA emitting galaxies during the Epoch of Reionization is controlled by both diffuse HI patches in large-scale bubble morphology and small-scale absorbers. To investigate the impact on LyA photons, we apply a novel combination of analytic and numerical calculations to three scenarios: (i) the `bubble' model, where only diffuse HI outside ionized bubbles is present; (ii) the `web' model, where HI exists only in overdense self-shielded gas; and (iii) the more realistic 'web-bubble' model, which contains both. Our analysis confirms that there is a degeneracy between the ionizati…
Recent studies have revealed intense UV metal emission lines in a modest sample of z>7 Lyman-alpha emitters, indicating a hard ionizing spectrum is present. If such high ionization features are shown to be common, it may indicate that extreme radiation fields play a role in regulating the visibility of Lyman-alpha in the reionization era. Here we present deep near-infrared spectra of seven galaxies with Lyman-alpha emission at 5.4<z<8.7 (including a newly-confirmed lensed galaxy at z=6.031) and three bright z>7 photometric targets. In nine sources we do not detect UV metal lines. However in th…
The next generation of telescopes aim to directly observe the first generation of galaxies that initiated the reionization process in our Universe. The Lyman Alpha (Lya) emission line is robustly predicted to be the most prominent intrinsic spectral feature of these galaxies, making it an ideal target to search for and study high redshift galaxies. Unfortunately the large Gunn-Peterson optical depth of the surrounding neutral intergalactic medium (IGM) is thought to render this line extremely difficult to detect prior to reionization. In this paper we demonstrate that the radiative transfer ef…
We model the transmission of the Lyman-alpha line through the circum- and intergalactic media around dark matter haloes expected to host Lyman-alpha emitters (LAEs) at z > 5.7, using the high-dynamic-range Sherwood simulations. We find very different CGM environments around more massive haloes (~10^11 M_sun) compared to less massive haloes (~10^9 M_sun) at these redshifts, which can contribute to a different evolution of the Lyman-alpha transmission from LAEs within these haloes. Additionally we confirm that part of the differential evolution could result from bright LAEs being more likely to …
Observations of distant galaxies play a key role in improving our understanding of the Epoch of Reionization (EoR). The observed Ly-alpha emission line strength - quantified by its restframe equivalent width (EW) - provides a valuable diagnostic of stellar populations and dust in galaxies during and after the EoR. In this paper we quantify the effects of star formation stochasticity on the predicted Ly-alpha EW in dwarf galaxies, using the publicly available code SLUG ('Stochastically Light Up Galaxies'). We compute the number of hydrogen ionizing photons, as well as flux in the Far UV for a s…
The observed scatter in intergalactic Lyman-$α$ opacity at $z \lesssim 6$ requires large-scale fluctuations in the neutral fraction of the intergalactic medium (IGM) after the expected end of reionization. Post-reionization models that explain this scatter invoke fluctuations in either the ionizing ultraviolet background (UVB) or IGM temperature. These models make very different predictions, however, for the relationship between Lyman-$α$ opacity and local density. Here we test these models using Lyman-$α$ emitting galaxies (LAEs) to trace the density field surrounding the longest and most opa…
The high-redshift intergalactic medium (IGM) and the primeval galaxy population are rapidly becoming the new frontier of extra-galactic astronomy. We investigate the IGM properties and their connection to galaxies at $z\geq5.5$ under different assumptions for the ionizing photon escape and the nature of dark matter, employing our novel THESAN radiation-hydrodynamical simulation suite, designed to provide a comprehensive picture of the emergence of galaxies in a full reionization context. Our simulations have realistic `late' reionization histories, match available constraints on global IGM pro…
The THESAN project: Lyman-alpha emitters as probes of ionized bubble sizes
Massachusetts Institute of Technology（麻省理工学院）；The University of Texas at Dallas（德克萨斯大学达拉斯分校）；Universidad ECCI（ECCI大学）；York University（约克大学）；The University of Tokyo（东京大学）；University of Edinburgh（爱丁堡大学）
Before the end of the epoch of reionization, the Hydrogen in the Universe was predominantly neutral. This leads to a strong attenuation of Ly$α$ lines of $z\gtrsim6$ galaxies in the intergalactic medium. Nevertheless, Ly$α$ has been detected up to very high redshifts ($z\sim9$) for several especially UV luminous galaxies. Here, we test to what extent the galaxy's local environment might impact the Ly$α$ transmission of such sources. We present an analysis of dedicated Hubble Space Telescope (HST) imaging in the CANDELS/EGS field to search for fainter neighbours around three of the most UV lumi…
We report the discovery of Lyman-alpha emission (Ly$α$) in the bright galaxy EGSY-2008532660 (hereafter EGSY8p7) using the MOSFIRE spectrograph at the Keck Observatory. First reported by Roberts-Borsani et al. (2015), it was selected for spectroscopic observations because of its photometric redshift ($z_{phot}=8.57^{+0.22}_{-0.43}$), apparent brightness (H$_{160}=25.26\pm0.09$) and red Spitzer/IRAC [3.6]-[4.5] color indicative of contamination by strong oxygen emission in the [4.5] band. With a total integration of $\sim$4.3 hours, our data reveal an emission line at $\simeq$11776 Å which we a…
The observability of Lyman-alpha emitting galaxies (LAEs) during the Epoch of Reionization can provide a sensitive probe of the evolving neutral hydrogen gas distribution, thus setting valuable constraints to distinguish different reionization models. In this study, we utilize the new THESAN suite of large-volume (95.5 cMpc) cosmological radiation-hydrodynamic simulations to directly model the Ly$α$ emission from individual galaxies and the subsequent transmission through the intergalactic medium. THESAN combines the AREPO-RT radiation-hydrodynamic solver with the IllustrisTNG galaxy formation…
Ringing of the Reionization: A first direct measurement of the intergalactic pressure smoothing scale at redshift z>4.2 as imprinted onto small-scale peculiar velocities in the Lyman-alpha forest
University of Hertfordshire（赫特福德大学）；Kavli Institute for Cosmology, University of Cambridge（剑桥大学卡弗里宇宙学研究所）；SISSA- International School for Advanced Studies（国际高等研究学院）；INFN – National Institute for Nuclear Physics（意大利国家核物理研究所）；IFPU, Institute for Fundamental Physics of the Universe（宇宙基础物理研究所）；INAF, Osservatorio Astronomico di Trieste（的里雅斯特天文台）；ICSC - Centro Nazionale di Ricerca in High Performance Computing, Big Data e Quantum Computing（高性能计算、大数据与量子计算国家研究中心）；Institute of Astronomy, University of Cambridge（剑桥大学天文学研究所）
We perform a systematic study of how the inhomogeneities in the Inter-Galactic Medium (IGM) affect the observability of Lyman Alpha Emitters (LAEs) around the Epoch of Reionization. We focus on the IGM close to the galaxies as the detailed ionization distribution and velocity fields of this region could significantly influence the scattering of Ly-alpha photons off neutral H atoms as they traverse the IGM after escaping from the galaxy. We simulate the surface brightness (SB) maps and spectra of more than 100 LAEs at z=7.7 as seen by an observer at z=0. To achieve this, we extract the source p…
