Lyα Luminosity Function Research Articles

MAMMOTH-Subaru. V. Effects of Cosmic Variance on Lyα Luminosity Functions at z = 2.2–2.3

Cosmic variance introduces significant uncertainties into galaxy number density properties when surveying the high-redshift Universe with a small volume. Such uncertainties produce the field-to-field variance σ g of galaxy numbers in observational astronomy, which significantly affects the luminosity function (LF) measurement of Lyα emitters (LAEs). For most previous Lyα LF studies, σ g is often adopted from predictions by cosmological simulations, but barely confirmed by observations. Measuring cosmic variance requires a huge sample over a large volume, exceeding the capabilities of most astronomical instruments. In this study, we demonstrate an observational approach for measuring the cosmic variance contribution for z ≈ 2.2 Lyα LFs. The LAE candidates are observed using the narrow band and broad band of the Subaru/Hyper Suprime-Cam in eight independent fields, making the total survey area ≃11.62 deg2 and a comoving volume of ≃8.71 × 106 Mpc3. We report a best-fit Schechter function with parameters α = −1.75 (fixed), LLyα*=5.95−0.96+1.22×1042 erg s−1, and ϕLyα*=5.26−1.27+1.65 × 10−4 Mpc−3 for the overall Lyα LFs. After clipping out the regions that may bias the cosmic variance measurements, we calculate σ g by sampling LAEs within multiple pointings on the field image. We investigate the relation between σ g and survey volume V, and fit a simple power-law σg=k×V105Mpc3β . We find best-fit values of −1.399−0.156+0.160 for β and 1.249−0.193+0.213 for k. We compare our measurements with predictions from simulations and find that the cosmic variance of LAEs is likely larger than that of general star-forming galaxies.

The miniJPAS and J-NEP surveys: Identification and characterization of the Lyα emitter population and the Lyα luminosity function at redshift 2.05 < z < 3.75

We present the Lyman-α (Lyα) luminosity function (LF) at 2.05 < z < 3.75, estimated from a sample of 67 Lyα-emitter (LAE) candidates in the Javalambre Physics of the Accelerating Universe Astronomical Survey (J-PAS) pathfinder surveys: miniJPAS and J-NEP. These two surveys cover a total effective area of ∼1.14 deg2 with 54 narrow band (NB) filters (FWHM ∼ 145 Å) across the optical range, with typical limiting magnitudes of ∼23. This set of NBs allowed us to probe Lyα emission in a wide and continuous range of redshifts. We developed a method for detecting Lyα emission for the estimation of the Lyα LF using the whole J-PAS filter set. We tested this method by applying it to the miniJPAS and J-NEP data. In order to compute the corrections needed to estimate the Lyα LF and to test the performance of the candidate selection method, we built mock catalogs. These include representative populations of LAEs at 1.9 < z < 4.5 as well as their expected contaminants, namely low-z galaxies and z < 2 quasi-stellar objects (QSOs). We show that our method is able to provide the Lyα LF at the intermediate-bright range of luminosity (43.5 ≲ log10(LLyα/erg s−1) ≲ 44.5) combining both miniJPAS and J-NEP. The photometric information provided by these surveys suggests that our samples are dominated by bright, Lyα-emitting active galactic nuclei (i.e., AGNs). At log10(LLyα/erg s−1) < 44.5, we fit our Lyα LF to a power law with a slope of A = 0.70 ± 0.25. We also fit a Schechter function to our data, obtaining the following: log10(Φ∗/Mpc−3) = −6.30−0.70+0.48, log10(L∗/erg s−1) = 44.85−0.32+0.50, and α = −1.65−0.27+0.29. Overall, our results confirm the presence of an AGN component at the bright end of the Lyα LF. In particular, we find no significant contribution of star-forming LAEs to the Lyα LF at log10(LLyα/erg s−1) > 43.5. This work serves as a proof of concept for the results that can be obtained with the upcoming data releases of the J-PAS survey.

A Spectroscopic Survey of Lyα Emitters and Lyα Luminosity Function at Redshifts 3.7 and 4.8

We present a spectroscopic survey of Lyα emitters (LAEs) at z ∼ 3.7 and z ∼ 4.8. The LAEs are selected using the narrowband technique based on the combination of deep narrowband and broadband imaging data in two deep fields, and then spectroscopically confirmed with the MMT multifiber spectrograph Hectospec. The sample consists of 71 LAEs at z ∼ 3.7 and 69 LAEs at z ∼ 4.8 over ∼1.5 deg2, making it one of the largest spectroscopically confirmed samples of LAEs at the two redshifts. Their Lyα luminosities are measured using the secure redshifts and deep photometric data, and span a range of ∼1042.5–1043.6 erg s−1, so these LAEs represent the most luminous galaxies at the redshifts in terms of Lyα luminosity. We estimate and correct sample incompletenesses and derive reliable Lyα luminosity function (LFs) at z ∼ 3.7 and 4.8 based on the two spectroscopic samples. We find that our Lyα LFs are roughly consistent (within a factor of 2−3) with previous measurements at similar redshifts that were derived from either photometric samples or spectroscopic samples. By comparing with previous studies in different redshifts, we find that the Lyα LFs decrease mildly from z ∼ 3.1 to z ∼ 5.7, supporting the previous claim of the slow LF evolution between z ∼ 2 and z ∼ 6. At z > 5.7, the LF declines rapidly toward higher redshift, partly due to the effect of cosmic reionization.

The contribution of faint Lyman-αemitters to extended Lyman-αhalos constrained by MUSE clustering measurements

Recent detections of extended Lyman-αhalos around Lyαemitters (LAEs) have been reported on a regular basis, but their origin is still under investigation. Simulation studies predict that the outer regions of the extended halos contain a major contribution from the Lyαemission of faint, individually undetected LAEs. To address this matter from an observational angle, we used halo occupation distribution (HOD) modeling to reproduce the clustering of a spectroscopic sample of 1265 LAEs at 3 < z < 5 from the MUSE-Wide survey. We integrated the Lyαluminosity function to estimate the background surface brightness due to discrete faint LAEs. We then extended the HOD statistics inwards towards small separations and computed the factor by which the measured Lyαsurface brightness is enhanced by undetected close physical neighbors. We considered various clustering scenarios for the undetected sources and compared the corresponding radial profiles. This enhancement factor from LAE clustering depends strongly on the spectral bandwidth Δvover which the Lyαemission is integrated and this value can amount to ≈20 − 40 for small values of Δv(around 200 − 400 km s−1) as achieved by recent studies utilizing integral-field spectrographic data. The resulting inferred Lyαsurface brightness of faint LAEs ranges between (0.4 − 2)×1020 erg s−1 cm−2 arcsec−2, with a very slow radial decline outwards. Our results suggest that the outer regions of observed Lyαhalos (R ≳ 50 pkpc) could indeed contain a strong component from external (but physically associated) LAEs, and may even be dominated by them. It is only for a relatively shallow faint-end slope of the Lyαluminosity function that this contribution from clustered LAEs would be rendered insignificant. We also confirm that the observed emission from the inner regions (R ≤ 20 − 30 pkpc) is too bright to be substantially affected by clustering. We compare our findings with predicted profiles from simulations and find good overall agreement. We outline possible future measurements to further constrain the impact of discrete undetected LAEs on observed extended Lyαhalos.

The Impact of Cosmic Variance on Inferences of Global Neutral Fraction Derived from Lyα Luminosity Functions during Reionization

We investigate the impact of field-to-field variation, deriving from cosmic variance, in measured Lyα emitter (LAE) luminosity functions (LFs) and this variation’s impact on inferences of the neutral fraction of the intergalactic medium (IGM) during reionization. We post-process a z = 7 IGM simulation to populate the dark matter halos with LAEs. These LAEs have realistic UV magnitudes, Lyα fluxes, and Lyα line profiles. We calculate the attenuation of Lyα emission in universes with varying IGM neutral fraction, . In a = 0.3 simulation, we perform 100 realizations of a mock 2 deg2 survey with a redshift window Δz = 0.5 and flux limit f Lyα > 1 × 10−17 erg s−1 cm−2; such a survey is typical in depth and volume of the largest LAE surveys conducted today. For each realization, we compute the LAE LF and use it to recover the input . Comparing the inferred values of across the ensemble of the surveys, we find that cosmic variance, deriving from large-scale structure and variation in the neutral gas along the sightline, imposes a floor in the uncertainty of when = 0.3. We explore mitigation strategies to decrease this uncertainty, such as increasing the volume, decreasing the flux limit, or probing the volume with many independent fields. Increasing the area and/or depth of the survey does not mitigate the uncertainty, but composing a survey with many independent fields is effective. This finding highlights the best strategy for LAE surveys aiming at constraining the of the universe during reionization.

The thesan project: Lyman-α emitter luminosity function calibration

ABSTRACT The observability of Lyα 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 ($L_\text{box} = 95.5\, \text{cMpc}$) cosmological radiation-hydrodynamic simulations to directly model the Lyα 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 model and includes high- and medium-resolution simulations designed to investigate the impacts of halo-mass-dependent escape fractions, alternative dark matter models, and numerical convergence. We find important differences in the Lyα transmission based on reionization history, bubble morphology, frequency offset from line centre, and galaxy brightness. For a given global neutral fraction, Lyα transmission reduces when low-mass haloes dominate reionization over high-mass haloes. Furthermore, the variation across sightlines for a single galaxy is greater than the variation across all galaxies. This collectively affects the visibility of LAEs, directly impacting observed Lyα luminosity functions (LFs). We employ Gaussian Process Regression using SWIFTEmulator to rapidly constrain an empirical model for dust escape fractions and emergent spectral-line profiles to match observed LFs. We find that dust strongly impacts the Lyα transmission and covering fractions of MUV ≲ −19 galaxies in $M_\text{vir} \gtrsim 10^{11}\, \text{M}_{\bigodot }$ haloes, such that the dominant mode of removing Lyα photons in non-LAEs changes from low-IGM transmission to high dust absorption around z ∼ 7.

Clustering dependence on Lyα luminosity from MUSE surveys at 3 < z < 6

We investigate the dependence of Lyα emitter (LAE) clustering on Lyα luminosity and connect the clustering properties of ≈L⋆ LAEs with those of much fainter ones, namely, ≈0.04L⋆. We use 1030 LAEs from the MUSE-Wide survey, 679 LAEs from MUSE-Deep, and 367 LAEs from the to-date deepest ever spectroscopic survey, the MUSE Extremely Deep Field. All objects have spectroscopic redshifts of 3 < z < 6 and cover a large dynamic range of Lyα luminosities: 40.15 < log(LLyα/erg s−1) < 43.35. We apply the Adelberger et al. K-estimator as the clustering statistic and fit the measurements with state-of-the-art halo occupation distribution (HOD) models. We find that the large-scale bias factor increases weakly with an increasing line luminosity. For the low-luminosity (log⟨LLyα/[erg s−1]⟩ = 41.22) and intermediate-luminosity (log⟨LLyα/[erg s−1]⟩ = 41.64) LAEs, we compute consistent bias factors blow = 2.43−0.15+0.15 and binterm. = 2.42−0.09+0.10, whereas for the high-luminosity (log⟨LLyα/[erg s−1]⟩ = 42.34) LAEs we calculated bhigh = 2.65−0.11+0.13. Consequently, high-luminosity LAEs occupy dark matter halos (DMHs) with typical masses of log(Mh/[h−1 M⊙]) = 11.09−0.09+0.10, while low-luminosity LAEs reside in halos of log(Mh/[h−1 M⊙]) = 10.77−0.15+0.13. The minimum masses to host one central LAE, Mmin, and (on average) one satellite LAE, M1, also vary with Lyα luminosity, growing from log(Mmin/[h−1M⊙]) = 10.3−0.3+0.2 and log(M1/[h−1 M⊙]) = 11.7−0.2+0.3 to log(Mmin/[h−1 M⊙]) = 10.7−0.3+0.2 and log(M1/[h−1 M⊙]) = 12.4−0.6+0.4 from low- to high-luminosity samples, respectively. The satellite fractions are ≲10% (≲20%) at 1σ (3σ) confidence level, supporting a scenario in which DMHs typically host one single LAE. We next bisected the three main samples into disjoint subsets to thoroughly explore the dependence of the clustering properties on LLyα. We report a strong (8σ) clustering dependence on Lyα luminosity, not accounting for cosmic variance effects, where the highest luminosity LAE subsample (log(LLyα/erg s−1) ≈ 42.53) clusters more strongly (bhighest = 3.13−0.15+0.08) and resides in more massive DMHs (log(Mh/[h−1M⊙] )= 11.43−0.10+0.04) than the lowest luminosity one (log(LLyα/erg s−1) ≈ 40.97), which presents a bias of blowest = 1.79−0.06+0.08 and occupies log(Mh/[h−1M⊙]) = 10.00−0.09+0.12 halos. We discuss the implications of these results for evolving Lyα luminosity functions, halo mass dependent Lyα escape fractions, and incomplete reionization signatures.

Lyα Emitting Galaxies (LAEs) at Cosmic Dawn: Implications and Predictions

The detection of Lyα emitting galaxies (LAEs) puts severe constraints on the reionization history. In this paper, we derive the properties of very high-z LAEs predicted in the only two reionization scenarios shown in a previous paper to be consistent with the current data on 15 independent evolving global (or averaged) cosmic properties regarding luminous objects and the intergalactic medium and the optical depth to electron scattering of ionized hydrogen to cosmic microwave background photons: one with a monotonic behavior, which is completed by z = 6, as commonly considered, and another one with a nonmonotonic behavior with two full ionization events at z = 6 and z = 10. We find that the Lyα luminosity functions of very high-z LAEs are very distinct in those two scenarios. Thus, comparing these predictions to the observations that will soon be available thanks to new instruments such as the James Webb Space Telescope, it should be possible to unveil the right reionization scenario. In the meantime, we can compare the predicted redshift distribution and UV (or Lyα) luminosities of very high-z LAEs to those of the few objects already observed at z > 7.5. By doing that, we find that such data are in tension with the single reionization scenario, while they are fully compatible with the double reionization scenario.

LAGER Lyα Luminosity Function at z ∼ 7: Implications for Reionization

Abstract We present a new measurement of the Lyα luminosity function (LF) at redshift z = 6.9, finding moderate evolution from z = 5.7 that is consistent with a fully or largely ionized z ∼ 7 intergalactic medium. Our result is based on four fields of the LAGER (Lyman Alpha Galaxies in the Epoch of Reionization) project. Our survey volume of 6.1 × 106 Mpc3 is double that of the next largest z ∼ 7 survey. We combine two new LAGER fields (WIDE12 and GAMA15A) with two previously reported LAGER fields (COSMOS and CDFS). In the new fields, we identify N = 95 new z = 6.9 Lyα emitter (LAEs) candidates, characterize our survey’s completeness and reliability, and compute Lyα LFs. The best-fit Schechter LF parameters for all four LAGER fields are in good general agreement. Two fields (COSMOS and WIDE12) show evidence for a bright-end excess above the Schechter function fit. We find that the Lyα luminosity density declines at the same rate as the UV continuum LF from z = 5.7 to 6.9. This is consistent with an intergalactic medium that was fully ionized as early as redshift z ∼ 7 or with a volume-averaged neutral hydrogen fraction of x H I < 0.33 at 1σ.

Near-IR narrow-band imaging with CIRCE at the Gran Telescopio Canarias: Searching for Lyα-emitters atz ∼ 9.3

Context.Identifying very high-redshift galaxies is crucial for understanding the formation and evolution of galaxies. However, many questions still remain, and the uncertainty on the epoch of reionization is large. In this approach, some models allow a double-reionization scenario, although the number of confirmed detections at very highzis still too low to serve as observational proof.Aims.The main goal of this project is studying whether we can search for Lyman-αemitters (LAEs) atz ∼ 9 using a narrow-band (NB) filter that was specifically designed by our team and was built for this experiment.Methods.We used the NB technique to select candidates by measuring the flux excess due to the Lyαemission. The observations were taken with an NB filter (full width at half minimum of 11 nm and central wavelengthλc = 1.257 μm) and the CIRCE near-infrared camera for the Gran Telescopio Canarias. We describe a data reduction procedure that was especially optimized to minimize instrumental effects. With a total exposure time of 18.3 h, the final NB image covers an area of ∼6.7 arcmin2, which corresponds to a comoving volume of 1.1 × 103Mpc3atz = 9.3.Results.We pushed the source detection to its limit, which allows us to analyze an initial sample of 97 objects. We detail the different criteria we applied to select the candidates. The criteria included visual verifications in different photometric bands. None of the objects resembled a reliable LAE, however, and we found no robust candidate down to an emission-line flux of 2.9 × 10−16erg s−1cm−2, which corresponds to a Lyαluminosity limit of 3 × 1044erg s−1. We derive an upper limit on the Lyαluminosity function atz ∼ 9 that agrees well with previous constraints. We conclude that deeper and wider surveys are needed to study the LAE population at the cosmic dawn.

The Magellan M2FS Spectroscopic Survey of High-z Galaxies: Lyα Emitters at z ≈ 6.6 and the Evolution of Lyα Luminosity Function over z ≈ 5.7–6.6

Abstract We present a sample of Lyα emitters (LAEs) at z ≈ 6.6 from our spectroscopic survey of high-redshift galaxies using the multi-object spectrograph M2FS on the Magellan Clay telescope. The sample consists of 36 LAEs selected by the narrowband (NB921) technique over nearly 2 deg2 in the sky. These galaxies generally have high Lyα luminosities spanning a range of ∼3 × 1042–7 × 1043 erg s−1, and include some of the most Lyα-luminous galaxies known at this redshift. They show a positive correlation between the Lyα line width and Lyα luminosity, similar to the relation previously found in z ≈ 5.7 LAEs. Based on the spectroscopic sample, we calculate a sophisticated sample completeness correction and derive the Lyα luminosity function (LF) at z ≈ 6.6. We detect a density bump at the bright end of the Lyα LF that is significantly above the best-fit Schechter function, suggesting that very luminous galaxies tend to reside in overdense regions that have formed large ionized bubbles around them. By comparing with the z ≈ 5.7 Lyα LF, we confirm that there is a rapid LF evolution at the faint end, but a lack of evolution at the bright end. The fraction of the neutral hydrogen in the intergalactic medium at z ≈ 6.6 estimated from such an evolution is about 0.3 ± 0.1, supporting a rapid and rather late process of cosmic reionization.

SILVERRUSH. XI. Constraints on the Lyα Luminosity Function and Cosmic Reionization at z = 7.3 with Subaru/Hyper Suprime-Cam

Abstract The Lyα luminosity function (LF) of Lyα emitters (LAEs) has been used to constrain the neutral hydrogen fraction in the intergalactic medium (IGM) and thus the timeline of cosmic reionization. Here we present the results of a new narrowband imaging survey for z = 7.3 LAEs in a large area of ∼3 deg2 with Subaru/Hyper Suprime-Cam. No LAEs are detected down to L Lyα ≃ 1043.2 erg s−1 in an effective cosmic volume of ∼2 × 106 Mpc3, placing an upper limit on the bright part of the z = 7.3 Lyα LF for the first time and confirming a decrease in bright LAEs from z = 7.0. By comparing this upper limit with the Lyα LF in the case of fully ionized IGM, which is predicted using an observed z = 5.7 Lyα LF on the assumption that the intrinsic Lyα LF evolves in the same way as the UV LF, we obtain the relative IGM transmission T Ly α IGM ( 7.3 ) / T Ly α IGM ( 5.7 ) < 0.77 and then the volume-averaged neutral fraction x H I(7.3) > 0.28. Cosmic reionization is thus still ongoing at z = 7.3, consistent with results from other x H I estimation methods. A similar analysis using literature Lyα LFs finds that at z = 6.6 and 7.0, the observed Lyα LF agrees with the predicted one, consistent with full ionization.

First HETDEX Spectroscopic Determinations of Lyα and UV Luminosity Functions at z = 2–3: Bridging a Gap between Faint AGNs and Bright Galaxies

Abstract We present Lyα and ultraviolet (UV)-continuum luminosity functions (LFs) of galaxies and active galactic nuclei (AGNs) at z = 2.0–3.5 determined by the untargeted optical spectroscopic survey of the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX). We combine deep Subaru imaging with HETDEX spectra resulting in 11.4 deg2 of fiber spectra sky coverage, obtaining 18,320 galaxies spectroscopically identified with Lyα emission, 2126 of which host type 1 AGNs showing broad (FWHM > 1000 km s−1) Lyα emission lines. We derive the Lyα (UV) LF over 2 orders of magnitude covering bright galaxies and AGNs in log L Ly α / [ erg s − 1 ] = 43.3 – 45.5 (−27 < M UV < −20) by the 1/V max estimator. Our results reveal that the bright-end hump of the Lyα LF is composed of type 1 AGNs. In conjunction with previous spectroscopic results at the faint end, we measure a slope of the best-fit Schechter function to be α Sch = − 1.70 − 0.14 + 0.13 , which indicates that α Sch steepens from z = 2–3 toward high redshift. Our UV LF agrees well with previous AGN UV LFs and extends to faint-AGN and bright-galaxy regimes. The number fraction of Lyα-emitting objects (X LAE) increases from M UV * ∼ − 21 to bright magnitude due to the contribution of type 1 AGNs, while previous studies claim that X Lyα decreases from faint magnitudes to M UV * , suggesting a valley in the X Lyα –magnitude relation at M UV * . Comparing our UV LF of type 1 AGNs at z = 2–3 with those at z = 0, we find that the number density of faint (M UV > −21) type 1 AGNs increases from z ∼ 2 to 0, as opposed to the evolution of bright (M UV < −21) type 1 AGNs, suggesting AGN downsizing in the rest-frame UV luminosity.

Lyα Line Properties at z = 3.78 and Their Environmental Dependence: A Case Study around a Massive Protocluster

Abstract Lyα-emitting galaxies (LAEs) are easily detectable in the high-redshift universe and are potentially efficient tracers of large-scale structure at early epochs, as long as their observed properties do not depend strongly on environment. We investigate the luminosity and equivalent width functions of LAEs in the overdense field of a protocluster at redshift z ≃ 3.78. Using a large sample of LAEs (many spectroscopically confirmed), we find that the Lyα luminosity distribution is well represented by a Schechter function with log ( L * / erg s − 1 ) = 43.26 − 0.22 + 0.20 and log ( ϕ * / Mpc − 3 ) = − 3.40 − 0.04 + 0.03 with α = −1.5. Fitting the equivalent width distribution as an exponential, we find a scale factor of ω = 79 − 15 + 15 Å. We also measured the Lyα luminosity and equivalent width functions using the subset of LAEs lying within the densest cores of the protocluster, finding similar values for L* and ω. Hence, despite having a mean overdensity more than 2× that of the general field, the shapes of the Lyα luminosity function and equivalent width distributions in the protocluster region are comparable to those measured in the field LAE population by other studies at similar redshift. While the observed Lyα luminosities and equivalent widths show correlations with the UV continuum luminosity in this LAE sample, we find that these are likely due to selection biases and are consistent with no intrinsic correlations within the sample. This protocluster sample supports the strong evolutionary trend observed in the Lyα escape fraction and suggests that LAEs at lower redshift can be on average significantly more dusty that their counterparts at higher redshift.

The Evolution of the Lyman-alpha Luminosity Function during Reionization

Abstract The time frame in which hydrogen reionization occurred is highly uncertain, but can be constrained by observations of Lyman-alpha (Lyα) emission from distant sources. Neutral hydrogen in the intergalactic medium (IGM) attenuates Lyα photons emitted by galaxies. As reionization progressed the IGM opacity decreased, increasing Lyα visibility. The galaxy Lyα luminosity function (LF) is thus a useful tool to constrain the timeline of reionization. In this work, we model the Lyα LF as a function of redshift, z = 5–10, and average IGM neutral hydrogen fraction, x ¯ Hɪ . We combine the Lyα luminosity probability distribution obtained from inhomogeneous reionization simulations with a model for the UV LF to model the Lyα LF. As the neutral fraction increases, the average number density of Lyα emitting galaxies decreases, and are less luminous, though for x ¯ Hɪ ≲ 0.4 there is only a small decrease in the Lyα LF. We use our model to infer the IGM neutral fraction at z = 6.6, 7.0, and 7.3 from observed Lyα LFs. We conclude that there is a significant increase in the neutral fraction with increasing redshift: x ¯ Hɪ ( z = 6.6 ) = 0.08 − 0.05 + 0.08 , x ¯ Hɪ ( z = 7.0 ) = 0.28 ± 0.05 and x ¯ Hɪ ( z = 7.3 ) = 0.83 − 0.07 + 0.06 . We predict trends in the Lyα luminosity density and Schechter parameters as a function of redshift and the neutral fraction. We find that the Lyα luminosity density decreases as the universe becomes more neutral. Furthermore, as the neutral fraction increases, the faint-end slope of the Lyα LF steepens, and the characteristic Lyα luminosity shifts to lower values; hence, we conclude that the evolving shape of the Lyα LF—not just its integral—is an important tool to study reionization.

The Evolution of the Ultraluminous Lyα Luminosity Function over z = 5.7–6.6

Abstract Ultraluminous Lyα emitting galaxies (ULLAEs) with erg s−1 near the epoch of reionization (z > 5) make up the bright end of the LAE luminosity function (LF) and may provide insight into the process of reionization, including the formation of ionized bubbles around these extreme systems. We present a spectroscopic LF for ULLAEs at z = 5.7. We used data from the HEROES ∼45 deg2 Subaru Hyper Suprime-Cam survey, which is centered on the North Ecliptic Pole and has both broadband (grizY) and narrowband (NB816 and NB921) imaging, to select candidate ULLAEs based on a NB816 excess and a strong broadband Lyman break. We spectroscopically observed 17 ULLAE candidates with DEIMOS on Keck II. We confirmed 12 as LAEs at z = 5.7, 9 of which are ULLAEs. The remaining sources are an active galactic nuclei at z = 5.7, an [O III]λ5007 emitter at z = 0.63, a red star, and two spectroscopic nondetections. Using the nine confirmed ULLAEs, we construct a ULLAE LF at z = 5.7. After applying a comprehensive incompleteness correction, we compare our new z = 5.7 LF with our recent z = 6.6 LF and with other LFs from the literature to look for evolution at the ultraluminous end. We find the overall ratio of the z = 5.7 to z = 6.6 ULLAE comoving number densities to be , which corresponds to an LF offset of dex.

The MUSE Extremely Deep Field: The cosmic web in emission at high redshift

We report the discovery of diffuse extended Lyα emission from redshift 3.1 to 4.5, tracing cosmic web filaments on scales of 2.5−4 cMpc. These structures have been observed in overdensities of Lyα emitters in the MUSE Extremely Deep Field, a 140 h deep MUSE observation located in the Hubble Ultra-Deep Field. Among the 22 overdense regions identified, five are likely to harbor very extended Lyα emission at high significance with an average surface brightness of 5 × 10−20 erg s−1 cm−2 arcsec−2. Remarkably, 70% of the total Lyα luminosity from these filaments comes from beyond the circumgalactic medium of any identified Lyα emitter. Fluorescent Lyα emission powered by the cosmic UV background can only account for less than 34% of this emission at z ≈ 3 and for not more than 10% at higher redshift. We find that the bulk of this diffuse emission can be reproduced by the unresolved Lyα emission of a large population of ultra low-luminosity Lyα emitters (< 1040 erg s−1), provided that the faint end of the Lyα luminosity function is steep (α ⪅ −1.8), it extends down to luminosities lower than 1038 − 1037 erg s−1, and the clustering of these Lyα emitters is significant (filling factor < 1/6). If these Lyα emitters are powered by star formation, then this implies their luminosity function needs to extend down to star formation rates < 10−4 M⊙ yr−1. These observations provide the first detection of the cosmic web in Lyα emission in typical filamentary environments and the first observational clue indicating the existence of a large population of ultra low-luminosity Lyα emitters at high redshift.

J-PLUS: Unveiling the brightest end of the Lyαluminosity function at 2.0 <z< 3.3 over 1000 deg2

We present the photometric determination of the bright end of the Lyαluminosity function (LF; atLLyα ≳ 1043.3 erg s−1) within four redshift windows (Δ z < 0.16) in the interval 2.2​ ≲ ​z​ ≲ ​3.3. Our work is based on the Javalambre Photometric Local Universe Survey (J-PLUS) first data release, which provides multiple narrow-band measurements over ∼1000 deg2, with limiting magnituder​ ∼ ​22. The analysis of high-zLyα-emitting sources over such a wide area is unprecedented and allows us to select approximately 14 500 hyper-bright (LLyα > 1043.3 erg s−1) Lyα-emitting candidates. We test our selection with two spectroscopic programs at the GTC telescope, which confirm ∼89% of the targets as line-emitting sources, with ∼64% being genuinez​ ∼ ​2.2 quasars (QSOs). We extend the 2.2​ ≲ ​z​ ≲ ​3.3 LyαLF for the first time aboveLLyα ∼ 1044 erg s−1and down to densities of ∼10−8 Mpc−3. Our results unveil the Schechter exponential decay of the brightest-end of the LyαLF in great detail, complementing the power-law component of previous determinations at 43.3 ≲ Log10(LLyα/erg s−1) ≲ 44. We measure Φ* = (3.33 ± 0.19)×10−6, Log(L*) = 44.65 ± 0.65, andα = −1.35 ± 0.84 as an average over the probed redshifts. These values are significantly different from the typical Schechter parameters measured for the LyαLF of high-zstar-forming Lyman-αemitters (LAEs). This implies thatz​ > ​2 AGNs/QSOs (likely dominant in our samples) are described by a structurally different LF from that used to describez​ > ​2 star-forming LAEs, namelyLQSOs*~ 100LLAEs*and ΦQSOs*~ 10−3ΦLAEs*, with the transition between the two LFs happening atLLyα ∼ 1043.5 erg s−1. This supports the scenario in which Lyα-emitting AGNs/QSOs are the most abundant class ofz​ ≳ ​2 Lyαemitters atLLyα ≳ 1043.3 erg s−1. Finally, we suggest that a significant number of thesez​ ≳ ​2 AGNs/QSOs (∼60% of our samples) are currently misclassified as stars based on their broad-band colours, but are identified for the first time as high-zline-emitters by our narrow-band-based selection.

The Magellan M2FS Spectroscopic Survey of High-redshift Galaxies: A Sample of 260 Lyα Emitters at Redshift z ≈ 5.7

Abstract We present a spectroscopic survey of Lyα emitters (LAEs) at z ≈ 5.7 using the multiobject spectrograph M2FS on the Magellan Clay telescope. This is part of a high-redshift galaxy survey carried out in several well-studied deep fields. These fields have deep images in multiple UV/optical bands, including a narrow NB816 band that has allowed an efficient selection of LAE candidates at z ≈ 5.7. Our sample consists of 260 LAEs and covers a total effective area of more than 2 deg2 on the sky. This is so far the largest (spectroscopically confirmed) sample of LAEs at this redshift. We use the secure redshifts and narrowband photometry to measure Lyα luminosities. We find that these LAEs span a Lyα luminosity range of erg s−1 and include some of the most luminous galaxies known at in terms of Lyα luminosity. Most of them have rest-frame equivalent widths between 20 and 300 Å, and more luminous Lyα emission lines tend to have broader line widths. We detect a clear offset of ∼20 Å between the observed Lyα wavelength distribution and the NB816 filter transmission curve, which can be explained by the intergalactic medium absorption of continua blueward of Lyα in the high-redshift spectra. This sample is being used to study the Lyα luminosity function and galaxy properties at z ≈ 5.7.

A Spectroscopic Survey of Lyα Emitters at z ≈ 3.1 over ∼1.2 Deg2

Abstract We present a spectroscopic survey of Lyα emitters (LAEs) at z ≈ 3.1 in the Subaru XMM-Newton Deep Survey Field. This field has deep imaging data in a series of broad and narrow bands, including two adjacent narrow bands NB497 and NB503 that have allowed us to efficiently select LAE candidates at z ≈ 3.1. Using spectroscopic observations on MMT Hectospec and Magellan M2FS, we obtained a sample of 166 LAEs at z ≈ 3.1 over an effective area of ∼1.2 deg2, including 16 previously known LAEs. This is so far the largest (spectroscopically confirmed) sample of LAEs at this redshift. We make use of the secure redshifts and multiband data to measure spectral properties such as Lyα luminosity and rest-frame UV slope. We derive a robust Lyα luminosity function (LF) that spans a luminosity range from ∼1042.0 to >1043.5 erg s−1. Significant overdense and underdense regions are detected in our sample, but the area coverage is wide enough to largely suppress the effect from such cosmic variance. Our Lyα LF is generally consistent with those from previous studies at z ∼ 3.1. At the brightest end of the LF, there is a tentative detection of a density excess that is not well described by the Schechter function. The comparison with the LFs at other redshifts suggests that the Lyα LF does not show significant evolution at 2 < z < 5. Finally, we build the composite spectra of the LAEs and detect the N v λ1239 and C iv λλ1548,1551 doublet emission lines at significance of ∼4σ, suggesting very hard radiation fields in (some of) these LAEs.