We report the discovery of a giant Lya emitter (LAE) with a Spitzer/IRAC counterpart near the reionization epoch at z=6.595. The giant LAE is found from the extensive 1 deg^2 Subaru narrow-band survey for z=6.6 LAEs in the Subaru/XMM-Newton Deep Survey (SXDS) field, and subsequently identified by deep spectroscopy of Keck/DEIMOS and Magellan/IMACS. Among our 207 LAE candidates, this LAE is not only the brightest narrow-band object with L(Lya) = 3.9+/-0.2 x 10^43 erg/s in our survey volume of 10^6 Mpc^3, but also a spatially extended Lya nebula with the largest isophotal area whose major axis is at least ~3''. This object is more likely to be a large Lya nebula with a size of >~17 kpc than to be a strongly-lensed galaxy by a foreground object. Our Keck spectrum with medium-high spectral and spatial resolutions suggests that the velocity width is v(FWHM)=251+/-21 km/s, and that the line-center velocity changes by ~60 km/s in a 10-kpc range. The stellar mass and star-formation rate are estimated to be 0.9-5.0 x 10^10 Mo and >34 Mo/yr, respectively, from the combination of deep optical to infrared images of Subaru, UKIDSS-Ultra Deep Survey, and Spitzer/IRAC. Although the nature of this object is not yet clearly understood, this could be an important object for studying cooling clouds accreting onto a massive halo, or forming-massive galaxies with significant outflows contributing to cosmic reionization and metal enrichment of inter-galactic medium.
We show that observations of high-redshift Ly-alpha emitters (LAEs) have the potential to provide definitive evidence for reionization in the near future. Using 200 Mpc radiative transfer simulations, we calculate the effect that patchy reionization has on the line profile, on the luminosity function, and, most interestingly, on the clustering of emitters for several realistic models of reionization. Reionization increases the measured clustering of emitters, and we show that this enhancement would be essentially impossible to attribute to anything other than reionization. Our results motivate…
We use a numerical simulation of cosmological reionization to estimate the likelihood of detecting Lyman-alpha emitting galaxies during the pre-reionization era. We show that it is possible to find galaxies even at z~9 that are barely affected by the dumping wing of the Gunn-Peterson absorption from the neutral IGM outside of their HII regions. The damping wing becomes rapidly more significant at z>9, but even at z>10 is it not inconceivable (although quite hard) to see a Lyman-alpha emission line from a star-forming galaxy.
Lyman-alpha emission from galaxies should be suppressed completely or partially at redshifts beyond reionization. Without knowing the instrinsic properties of galaxies at z = 6.5, this attenuation is hard to infer in any one source, but can be infered from a comparison of luminosity functions of lyman-alpha emitters at redshifts just before and after reionization. We combine published surveys of widely varying depths and areas to construct luminosity functions at z=6.5 and 5.7, where the characteristic luminosity L_star and density phi_star are well constrained while the faint-end slope of the…
At redshifts beyond z>6, as the mean fraction of neutral hydrogen x_HI in the intergalactic medium (IGM) increases, the line flux of Lyman alpha (Lya) emitters can be significantly suppressed, which can result in a decrease in the observed number of emitters at a given Lya flux. However, cosmological HII regions surrounding the Lya emitting galaxies alleviate these effects. We use simple models of the Lya line suppression that incorporate the presence of HII regions to predict the overall effect of the Lya absorption on the Lya luminosity function. We find, in agreement with other recent studi…
In Loeb & Rybicki (1999; paper I) it was shown that before reionization, the scattering of \lya photons from a cosmological source might lead to a fairly compact ($\sim 15''$) \lya halo around the source. Observations of such halos could constrain the properties of the neutral intergalactic medium (IGM), and in particular yield the cosmological density parameters of baryons and matter on scales where the Hubble flow is unperturbed. Paper I did not treat the polarization of this scattered radiation, but did suggest that the degree of such polarization might be large. In this Letter we report on…
We discuss new observational constraints on the abundance of faint high redshift Lyman-alpha emitters secured from a deep Keck near-infrared spectroscopic survey which utilizes the strong magnification provided by lensing galaxy clusters at intermediate redshift (z=0.2-0.5). In each of 9 clusters we have undertaken a systematic `blind' search for line emission with NIRSPEC in the J-band within carefully-selected regions which offer very high magnifications (>10-50x) for background sources with redshifts z~10. The high magnification enables the detection of emission at unprecedented limits (10^…
We use a semi-analytic model of Lyman alpha emitters (LAEs) to constrain the reionization history. By considering two physically motivated scenarios in which reionization ends either early (ERM, z_i ~ 7) or late (LRM, z_i ~ 6), we fix the global value of the IGM neutral fraction (e.g. chi_{HI}=3 times 10^{-4}, 0.15 at z=6.56 for the ERM and LRM, respectively) leaving only the star formation efficiency and the effective escape fraction of Lya photons as free parameters. The ERM fits the observed LAE luminosity function (LF) at z=5.7 and 6.56 requiring no redshift evolution or mass dependence of…
We report an extensive search for Lyman-alpha emitters (LAEs) at z=6.5 in the Subaru Deep Field. Subsequent spectroscopy with Subaru and Keck identified eight more LAEs, giving a total of 17 spectroscopically confirmed LAEs at z=6.5. Based on this spectroscopic sample of 17, complemented by a photometric sample of 58 LAEs, we have derived a more accurate Lyman-alpha luminosity function of LAEs at z=6.5, which reveals an apparent deficit at the bright end of ~0.75 mag fainter L*, compared with that observed at z=5.7. The difference in the LAE luminosity functions between z=5.7 and 6.5 is signif…
We present results from a blind, spectroscopic search for redshift 5.7 LyA emission-line galaxies at Keck I. Using a band-limiting filter and custom slitmask, the LRIS detector was covered with low resolution spectra in the 8100 - 8250 A atmospheric window which contains no bright night sky emission lines. Nine objects with line fluxes greater than our flux limit of 6e-18 erg/s/cm2 were found in the ~5.1 square arcminute field. Follow up observations indicate none of these are z=5.7 LyA emitters -- a result which places strong limits on evolution scenarios for LyA emitters between redshift 3 a…
Radio, optical and X-ray observations of the powerful radio galaxy PKS 1138-262 at z=2.156 have suggested that this galaxy is a massive galaxy in the center of a forming cluster. We have imaged 1138-262 and the surrounding 38 square arcminute field with the Very Large Telescope in a broad band and a narrow band encompassing the redshifted Lya emission. We detect 50 objects with rest equivalent width larger than 20 A and a luminous, highly extended Lya halo around 1138-262. If the radio galaxy is at the center of a forming cluster, these objects are candidate Lya emitting cluster galaxies.
We made a narrowband NB973 (bandwidth of 200A at 9755A) imaging of the Subaru Deep Field (SDF) and found two z=7 Lyman alpha emitter (LAE) candidates down to NB973=24.9. Carrying out deep follow-up spectroscopy, we identified one of them as a real z=6.96 LAE. This has shown that galaxy formation was in progress just 750 Myr after the Big Bang. Meanwhile, the Lyman alpha line luminosity function of LAE is known to decline from z=5.7 to 6.6 in the SDF. L* at z=6.6 is 40-60% of that at z=5.7. We also confirm that the number density of z=7 LAE is only 17% of the density at z=6.6 comparing the late…
We investigate the potential of exploiting Lya Emitters (LAEs) to constrain the volume-weighted mean neutral hydrogen fraction of the IGM, x_H, at high redshifts (specifically z~9). We use "semi-numerical'' simulations to efficiently generate density, velocity, and halo fields at z=9 in a 250 Mpc box, resolving halos with masses M>2.2e8 solar masses. We construct ionization fields corresponding to various values of x_H. With these, we generate LAE luminosity functions and "counts-in-cell'' statistics. As in previous studies, we find that LAEs begin to disappear rapidly when x_H > 0.5. Constrai…
Observations of high-redshift Ly-alpha sources are a major tool for studying the high-redshift Universe. We discuss the effect of the reionizing intergalactic medium on the observability of Ly-alpha sources based on large simulations of early structure formation with radiative transfer. This takes into account self-consistently the reionization history, density, velocity and ionization structures and nonlinear source clustering. We find that all fields are highly anisotropic and as a consequence there are very large variations in opacity among the different lines-of-sight. The velocity effects…
Lyman alpha galaxies at high redshifts offer a powerful probe of both the formation of galaxies and the reionization of the intergalactic medium. Lyman alpha line emission is an efficient tool for identifying young galaxies at high redshift, because it is strong in systems with young stars and little or no dust-- properties expected in galaxies undergoing their first burst of star-formation. Lyman alpha galaxies also provide a robust test of the reionization epoch that is independent of Gunn-Peterson trough observations in quasar spectra and is better able to distinguish line center optical de…
We present a new photometric search for high-z galaxies hosting Population III (PopIII) stars based on deep intermediate-band imaging observations obtained in the Subaru Deep Field (SDF), by using Suprime-Cam on the Subaru Telescope. By combining our new data with the existing broad-band and narrow-band data, we searched for galaxies which emit strongly both in Ly_alpha and in HeII 1640 (``dual emitters'') that are promising candidates for PopIII-hosting galaxies, at 3.93<z<4.01 and 4.57<z<4.65. Although we found 10 ``dual emitters'', most of them turn out to be [OII]-[OIII] dual emitters or H…
Recent observations imply that the observed number counts of Lya Emitters (LAEs) evolved significantly between z=5.7 and z=6.5. It has been suggested that this was due to a rapid evolution in the ionisation state, and hence transmission of the IGM which caused Lya flux from z=6.5 galaxies to be more strongly suppressed. In this paper we consider the joint evolution of the Lya and UV luminosity functions (LFs) and show that the IGM transmission evolved between z=6.5 and z=5.7 by a factor 1.1 <R < 1.8 (95% CL). This result is insensitive to the underlying model of the Lya LF (as well as cosmic v…
We present Spitzer Space Telescope observations of the z=2.38 lya-emitter over-density associated with galaxy cluster J2143-4423, the largest known structure (110 Mpc) above z=2. We imaged 22 of the 37 known lya-emitters within the filament-like structure, using the MIPS 24um band. We detected 6 of the lya-emitters, including 3 of the 4 clouds of extended (>50 kpc) lyman alpha emission, also known as Lya Blobs. Conversion from rest-wavelength 7um to total far-infrared luminosity using locally derived correlations suggests all the detected sources are in the class of ULIRGs, with some reaching …
The Aim of our study is to understand the variety of observed Lyman-alpha (Lya) line profiles and strengths in Lyman Break Galaxies (LBGs) and Lya emitters (LAEs), the physical parameters governing them, and hence deriving constraints on the gas and dust content and stellar populations of these objects. Using our 3D Lya radiation transfer code including gas and dust (Verhamme et al. 2006), we fit 11 LBGs from the FORS Deep Field with redshifts between 2.8 and 5 observed by Tapken et al. (2007). A simple geometry of a spherically expanding shell of HI is adopted. RESULTS : The variety of observ…
Numerous surveys are underway or planned that aim to exploit the Lyman-alpha emission line as a probe of the distant universe. We investigate the reliability of such high-z Lya studies and the validity of the conclusions that are based upon them. We examine whether reliable Lya fluxes (F_Lya) and equivalent widths (W_Lya) can be estimated from narrowband imaging surveys and whether any observational biases may be present. We have developed software to simulate the observed line and continuum properties of synthetic LAEs in the distant universe by adopting various typical observational techniqu…
We present luminosity functions (LFs) and various properties of Lya emitters (LAEs) at z=3.1, 3.7, and 5.7, in a 1 deg^2 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 ~10^6 Mpc^3 with a limiting Lya luminosity of ~3x10^42 erg/s. We derive the LFs of Lya and UV-continuum (~1500 Å) for each redshift, taking into account the statistical error and the field-to-field variation. …
Concurrent observations of Lyman continuum (LyC) and Lyman-alpha (Lya) emission escaping from star-forming systems at low redshift are essential to understanding the physics of reionization at high redshift (z >~ 6). Some have suggested reionization is dominated by numerous small galaxies with LyC escape fractions f_e ~ 10%, while others suggest mini-quasars with higher f_e might also play a role. At z > 3, direct observation of LyC leakage becomes progressively more improbable due to the increase of intervening Ly limit systems, leaving Lya as the primary diagnostic available to the James Web…
We report the discovery of a Lyman-alpha-emitting galaxy at redshift z=6.545 serendipitously identified in the course of spectroscopic follow-up of hard X-ray sources on behalf of the Serendipitous Extragalactic X-Ray Source Identification (SEXSI) survey. The line flux of the galaxy, 2.1e-17 erg/cm2/s, is similar to line fluxes probed by narrow-band imaging surveys; the 5.2 square-arcminutes surveyed implies a surface density of z~6.5 Lyman-alpha emitters somewhat higher than that inferred from narrow-band surveys. This source marks the sixth Lyman-alpha-emitting galaxy identified at z~6.5, a …
We measure several properties of the reionization process and the corresponding low-frequency 21-cm signal associated with the neutral hydrogen distribution, using a large volume, high resolution simulation of cosmic reionization. The brightness temperature of the 21-cm signal is derived by post-processing this numerical simulation with a semi-analytical prescription. Our study extends to high redshifts (z ~ 25) where, in addition to collisional coupling, our post-processed simulations take into account the inhomogeneities in the heating of the neutral gas by X-rays and the effect of an inhomo…
We report on early results from deep and wide-field narrow-band imaging on a 543 arcmin^2 area of the Subaru Deep Field. We find 87 Lya emitters (LAEs) at z=4.86(+/-0.03) which are photometrically selected by a combination of two broad bands (R and i') and one narrow band (NB711; 7126A FWHM=73A). We derive the luminosity functions (LFs) of the LAEs at Lya luminosity and at UV-continuum (1700A) luminosity. The LFs show little evolution between z=3.4 and z=4.86 either in Lya or UV-continuum emission. The amplitude of the LAE LF tends to decline at the bright magnitudes more rapidly than that of …
We report the discovery of a Lyman alpha emitting galaxy at z = 6.518. The single line was found in the 43 square arcmin VLT/FORS field by slitless spectroscopy limited to the atmospheric window at 9100 A (sampling Lya at 6.4 < z < 6.6). Its counterpart is undetected in a deep I band image and the line has an asymmetric appearance in a deeper follow-up spectrum. There are no plausible line identifications except for Lya with a flux of 1.9x10^-17 erg/s/cm2 and rest frame equivalent width > 80 A. The lower limit to the star formation rate density at z = 6.5 derived from our complete sample is 5x…
We present a new theoretical model for the luminosity functions (LFs) of Lyman alpha (Lya) emitting galaxies in the framework of hierarchical galaxy formation. We extend a semi-analytic model of galaxy formation that reproduces a number of observations for local and high-z galaxies, without changing the original model parameters but introducing a physically-motivated modelling to describe the escape fraction of Lya photons from host galaxies (f_esc). Though a previous study using a hierarchical clustering model simply assumed a constant and universal value of f_esc, we incorporate two new effe…
We present Keck/LRIS optical spectra of 17 Lya-emitting galaxies and one Lyman break galaxy at z=4.5 discovered in the Large Area Lyman Alpha (LALA) survey. The survey has identified a sample of ~350 candidate Lya-emitting galaxies at z=4.5 in a search volume of 1.5 x 10^6 comoving Mpc^3. We targeted 25 candidates for spectroscopy; hence, the 18 confirmations presented herein suggest a selection reliability of 72%. The large equivalent widths (median W(rest)~80 A) but narrow physical widths (v < 500 km/s) of the Lya emission lines, along with the lack of accompanying high-ionization state emis…
We describe preliminary results from an ultra-sensitive, spectroscopic emission-line survey and illustrate the challenges inherent in identifying high-redshift LyA emitters. Our multi-slit windows technique complements other types of emission-line surveys. Narrowband imaging surveys cover large areas of sky but only detect much brighter objects. Longslit spectra taken along cluster caustics yield intrinsically fainter lensed LyA emitters but probe small volumes of space. We have observed the COSMOS deep field and a field at 15h +00. To a line flux of a few times 10^-18 erg/s/cm^2, we found 150…
We present deep HST/ACS observations in g,r,i,z towards the z=4.1 radio galaxy TN J1338-1942 and its overdensity of >30 spectroscopically confirmed Lya emitters (LAEs). We select 66 g-band dropouts to z=27, 6 of which are also a LAE. Although our color-color selection results in a relatively broad redshift range centered on z=4.1, the field of TN J1338-1942 is richer than the average field at the >5 sigma significance, based on a comparison with GOODS. The angular distribution is filamentary with about half of the objects clustered near the radio galaxy, and a small, excess signal (2 sigma) in…
We use numerical simulations of hydrogen reionization by stellar sources in the context of LCDM cosmogonies to investigate the 21 (1+z) cm radio signal expected from the diffuse intergalactic medium (IGM) prior to the epoch of reionization breakthrough at redshift z_ion. Two reionization scenarios are analyzed in details: an `early reionization' case with z_ion~13, consistent with the recent discovery by the WMAP satellite of a large optical depth to Thomson scattering, and a `late reionization' case with z_ion~8. It is a generic prediction of these models that the background of Lyalpha photon…
If the universe was reionized by O and B stars in an early population of galaxies, the associated supernovae should have enriched the universe to a mean metallicity $\bar Z = 10^{-5} (1+ n_{rec})$, where $n_{rec}$ is the mean number of times that each baryon recombined during the reionization era. This is consistent with recent observations of the metallicity in the Lya forest at $z\simeq 3$. The mean surface brightness observable at present from the galaxies that produced these heavy elements, in the rest-frame wavelengths $1216Å< λ\lesssim 2500Å$, should be $\sim 10^{-6} (\bar Z/10^{-4}) (Ω_…
(Abridged) We review recent observations that suggest the star formation rate density is declining over 3$<z<$7 and illustrate the challenges that this poses in explaining the assembled stellar mass in z$\sim$6 galaxies deduced from Spitzer data. A plausible conclusion is a vigorous period of earlier star formation. Prior to JWST and TMT, strong lensing offers a unique probe of the extent of this earlier activity. We discuss the first results of a blind spectroscopic survey of lensing clusters for 8.5$<z<$10 Ly$α$ emitters using NIRSPEC which is achieving a limiting star formation rate of 0.1 …
