Bright LAEs Research Articles

UV and Lyα Halos of Lyα Emitters across Environments at z = 2.84* * This research is based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

We present UV and Lyα radial surface brightness (SB) profiles of Lyα emitters (LAEs) at z = 2.84 detected with the Hyper Suprime-Cam on the Subaru Telescope. The depth of our data, together with the wide-field coverage including a protocluster, enable us to study the dependence of Lyα halos (LAHs) on various galaxy properties, including Mpc scale environments. UV and Lyα images of 3490 LAEs are extracted, and stacking the images yields SB sensitivity of in Lyα, reaching the expected level of optically thick gas illuminated by the UV background at z ∼ 3. Fitting of the two-component exponential function gives the scale-lengths of 1.56 ± 0.01 and 10.4 ± 0.3 pkpc. Dividing the sample according to their photometric properties, we find that, while the dependence of halo scale-length on environment outside of the protocluster core is not clear, LAEs in the central regions of protoclusters appear to have very large LAHs, which could be caused by combined effects of source overlapping and diffuse Lyα emission from cool intergalactic gas permeating the forming protocluster core irradiated by active members. For the first time, we identify UV halos around bright LAEs that are probably due to a few lower-mass satellite galaxies. Through comparison with recent numerical simulations, we conclude that, while scattered Lyα photons from the host galaxies are dominant, star formation in satellites evidently contributes to LAHs, and that fluorescent Lyα emission may be boosted within protocluster cores at cosmic noon and/or near bright QSOs.

Can luminous Lyman alpha emitters at z ≃ 5.7 and z ≃ 6.6 suppress star formation?

ABSTRACT Addressing how strong UV radiation affects galaxy formation is central to understanding their evolution. The quenching of star formation via strong UV radiation (from starbursts or active galactic nuclei) has been proposed in various scenes to solve certain astrophysical problems. Around luminous sources, some evidence of decreased star formation has been found but is limited to a handful of individual cases. No direct, conclusive evidence on the actual role of strong UV radiation in quenching star formation has been found. Here, we present statistical evidence of decreased number density of faint (AB magnitude ≥ 24.75 mag) Ly α emitters (LAEs) around bright (AB magnitude < 24.75 mag) LAEs even when the radius goes up to 10 pMpc for z ≃ 5.7 LAEs. A similar trend is found for z ≃ 6.6 LAEs but only for faint LAEs within 1 pMpc radius from the bright LAEs. We use a large sample of 1077 (962) LAEs at z ≃ 5.7 (z ≃ 6.6) selected in total areas of 14 (21) deg2 with Subaru/Hyper Suprime-Cam narrow-band data, and thus, the result is of statistical significance for the first time at these high redshift ranges. A simple analytical calculation indicates that the radiation from the central LAE is not enough to suppress LAEs with AB mag ≥ 24.75 mag around them, suggesting additional physical mechanisms we are unaware of are at work. Our results clearly show that the environment is at work for the galaxy formation at z ∼ 6 in the Universe.

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.

CHORUS. II. Subaru/HSC Determination of the Lyα Luminosity Function at z = 7.0: Constraints on Cosmic Reionization Model Parameter

We present the Ly$\alpha$ luminosity function (LF) derived from 34 Ly$\alpha$ emitters (LAEs) at $z=7.0$ on the sky of $3.1$ deg$^2$, the largest sample compared to those in the literature obtained at a redshift $z\gtrsim7$. The LAE sample is made by deep large-area Subaru narrowband observations conducted by the Cosmic HydrOgen Reionization Unveiled with Subaru (CHORUS) project. The $z=7.0$ Ly$\alpha$ LF of our project is consistent with those of the previous DECam and Subaru studies at the bright and faint ends, respectively, while our $z=7.0$ Ly$\alpha$ LF has uncertainties significantly smaller than those of the previous study results. Exploiting the small errors of our measurements, we investigate the shape of the faint to bright-end Ly$\alpha$ LF. We find that the $z=7.0$ Ly$\alpha$ LF shape can be explained by the steep slope of $\alpha \simeq -2.5$ suggested at $z=6.6$, and that there is no clear signature of a bright-end excess at $z\simeq 7$ claimed by the previous work, which was thought to be made by the ionized bubbles around bright LAEs whose Ly$\alpha$ photons could easily escape from the partly neutral IGM at $z \simeq 7$. We estimate the Ly$\alpha$ luminosity densities (LDs) with Ly$\alpha$ LFs at $z\simeq 6-8$ given by our and the previous studies, and compare the evolution of the UV-continuum LD estimated with dropouts. The Ly$\alpha$ LD monotonically decreases from $z\sim 6$ to $8$, and evolves stronger than the UV-continuum LD, indicative of the Ly$\alpha$ damping wing absorption of the IGM towards the heart of the reionization epoch.

Spectroscopic Investigation of a Reionized Galaxy Overdensity at z = 7

Abstract We present deep spectroscopic follow-up observations of the Bremer Deep Field (BDF), where the two z ∼ 7 bright Lyα emitters (LAE) BDF521 and BDF3299 were previously discovered by Vanzella et al. and where a factor of ∼3–4 overdensity of faint LBGs has been found by Castellano et al. We confirm a new bright Lyα emitter, BDF2195, at the same redshift of BDF521, z = 7.008 and at only ∼90 kpc physical distance from it, confirming that the BDF area is likely an overdense, reionized region. A quantitative assessment of the Lyα fraction shows that the number of detected bright emitters is much higher than the average found at z ∼ 7, suggesting a high Lyα transmission through the intergalactic medium. However, the line visibility from fainter galaxies is at odds with this finding, as no Lyα emission is found in any of the observed candidates with M UV > −20.25. This discrepancy can be understood either if some mechanism prevents Lyα emission from fainter galaxies within the ionized bubbles from reaching the observer, or if faint galaxies are located outside the reionized area and bright LAEs are solely responsible for the creation of their own H ii regions. A thorough assessment of the nature of the BDF region and of its sources of re-ionizing radiation will be made possible by James Webb Space Telescope spectroscopic capabilities.

SILVERRUSH. IV. Lyα luminosity functions at z = 5.7 and 6.6 studied with ∼1300 Lyα emitters on the 14–21 deg2 sky

Abstract We present the Lyα luminosity functions (LFs) at z = 5.7 and 6.6 derived from a new large sample of 1266 Lyα emitters (LAEs) identified in total areas of 14 and 21 deg2, respectively, based on the early narrowband data of the Subaru/Hyper Suprime-Cam survey. Together with careful Monte Carlo simulations that account for the incompleteness of the LAE selection and the flux estimate systematics in the narrowband imaging, we have determined the Lyα LFs with unprecedentedly small statistical and systematic uncertainties in a wide Lyα luminosity range of 1042.8–43.8 erg s−1. We obtain best-fit Schechter parameters of $L^{*}_{\mathrm{Ly}\alpha } = 1.6^{+2.2}_{-0.6} \ (1.7^{+0.3}_{-0.7}) \times 10^{43}\:\mathrm{erg}\:\mathrm{s}^{-1}$, $\phi ^{*}_{\mathrm{Ly}\alpha } = 0.85^{+1.87}_{-0.77} \ (0.47^{+1.44}_{-0.44}) \times 10^{-4}\:\mathrm{Mpc}^{-3}$, and $\alpha = -2.6^{+0.6}_{-0.4} \ (-2.5^{+0.5}_{-0.5})$ at z = 5.7 (6.6). We confirm that our best-estimate Lyα LFs are consistent with the majority of the previous studies, but find that our Lyα LFs do not agree with the high number densities of LAEs recently claimed by Matthee/Santos et al.’s studies that may overcorrect the incompleteness and the flux systematics. Our Lyα LFs at z = 5.7 and 6.6 show an indication that the faint-end slope is very steep (α ≃ −2.5), although it is also possible that the bright-end LF results are enhanced by systematic effects such as the contribution from AGNs, blended merging galaxies, and/or large ionized bubbles around bright LAEs. Comparing our Lyα LF measurements with four independent reionization models, we estimate the neutral hydrogen fraction of the intergalactic medium to be $x_\mathrm{H\,{\small I}} = 0.3 \pm 0.2$ at z = 6.6, which is consistent with the small Thomson scattering optical depth obtained by Planck 2016.

Identification of the brightest Lyα emitters at z = 6.6: implications for the evolution of the luminosity function in the reionization era

Using wide field narrow-band surveys, we provide a new measurement of the $z=6.6$ Lyman-$\alpha$ Emitter (LAE) luminosity function (LF), which constraints the bright end for the first time. We use a combination of archival narrow-band NB921 data in UDS and new NB921 measurements in SA22 and COSMOS/UltraVISTA, all observed with the Subaru telescope, with a total area of $\sim 5$ deg$^2$. We exclude lower redshift interlopers by using broad-band optical and near-infrared photometry and also exclude three supernovae with data split over multiple epochs. Combining the UDS and COSMOS samples we find no evolution of the bright end of the Ly$\alpha$ LF between $z=5.7$ and $6.6$, which is supported by spectroscopic follow-up, and conclude that sources with \emph{Himiko}-like luminosity are not as rare as previously thought, with number densities of $\sim 1.5\times10^{-5}$ Mpc$^{-3}$. Combined with our wide-field SA22 measurements, our results indicate a non-Schechter-like bright end of the LF at $z=6.6$ and a different evolution of \emph{observed} faint and bright LAEs. This differential evolution is also seen in the spectroscopic follow-up of UV selected galaxies and is now also confirmed for Ly$\alpha$ emitters, and we argue that it may be an effect of re-ionisation. Using a toy-model, we show that such differential evolution of the LF is expected, since brighter sources are able to ionise their surroundings earlier, such that Ly$\alpha$ photons are able to escape. Our targets are excellent candidates for detailed follow-up studies and provide the possibility to give a unique view on the earliest stages in the formation of galaxies and re-ionisation process.

The Subaru/XMM‐NewtonDeep Survey (SXDS). IV. Evolution of Lyα Emitters from \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $z=3.1$ \end{document} to 5.7 in the 1 deg2Field: Luminosity Functions and AGN

We present luminosity functions (LFs) and various properties of Lyα emitters (LAEs) at z = 3.1, 3.7, and 5.7, in a 1 deg2 sky of the Subaru/XMM–Newton Deep Survey (SXDS) Field. We obtain a photometric sample of 858 LAE candidates based on deep Subaru Suprime-Cam imaging data and a spectroscopic sample of 84 confirmed LAEs from Subaru FOCAS and VLT VIMOS spectroscopy in a survey volume of ~106 Mpc3 with a limiting Lyα luminosity of ~3 × 1042 ergs s−1. We derive the LFs of the Lyα and UV continuum (1500 A) for each redshift, taking into account the statistical error and the field-to-field variation. We find that the apparent Lyα LF shows no significant evolution between z = 3.1 and 5.7 within factors of 1.8 and 2.7 in L* and *, respectively. On the other hand, the UV LF of LAEs increases from z = 3.1 to 5.7, indicating that galaxies with Lyα emission are more common at earlier epochs. We identify six LAEs with AGN activities from our spectra combined with VLA, Spitzer, and XMM-Newton data. Among the photometrically selected LAEs at z = 3.1 and 3.7, only 1% show AGN activities, while the brightest LAEs with log L(Ly α) 43.4–43.6 ergs s−1 appear to always host AGNs. Our LAEs are bluer in UV-continuum color than dropout galaxies, suggesting lower extinction and/or younger stellar populations. Our stacking analyses provide upper limits to the radio luminosity and the fHe II/fLyα line fraction and constrain the hidden star formation (+low-luminosity AGN) and the primordial population in LAEs.

Lyα Emitters in Hierarchical Galaxy Formation

We present a new theoretical model for the luminosity functions (LFs) of Lyα-emitting galaxies in the framework of hierarchical galaxy formation. We extend a semianalytical model of galaxy formation that reproduces a number of observations for local and high-z galaxies, without changing the original model parameters but with the introduction of physically motivated modeling to describe the escape fraction of Lyα photons from host galaxies (f). Although previous studies using hierarchical clustering models simply assumed a constant and universal value of f, we incorporate two new effects on f: extinction by interstellar dust and galaxy-scale outflows induced as star formation feedback. It is found that the new model nicely reproduces all the observed Lyα LFs of Lyα emitters (LAEs) with redshifts in the range z ~ 3-6. In particular, the surprisingly small evolution of the observed LAE Lyα LFs as compared with the dark halo mass function is naturally reproduced. Our model predicts that galaxies with strong outflows and f ~ 1 should dominate the observed LFs. This is also consistent with available observations, whereas the simple universal f model requires f 1 in order not to overproduce the brightest LAEs. On the other hand, we find that our model significantly overpredicts LAEs at z 6, and that absorption of Lyα photons by neutral hydrogen in the intergalactic medium (IGM) provides a reasonable interpretation of this discrepancy. This indicates that the IGM neutral fraction xH I rapidly evolves from xH I 1 at z 6 to a value of order unity at z ~ 6-7, which is broadly consistent with other observational constraints on the history of reionization.