Faint Lyman-$\alpha$ (Ly$\alpha$) emitters become increasingly rarer towards the re-ionisation epoch (z~6-7). However, observations from a very large (~5deg$^2$) Ly$\alpha$ survey at z=6.6 (Matthee et al. 2015) show that this is not the case for the most luminous emitters. Here we present follow-up observations of the two most luminous z~6.6 Ly$\alpha$ candidates in the COSMOS field: `MASOSA' and `CR7'. We used X-SHOOTER, SINFONI and FORS2 (VLT), and DEIMOS (Keck), to confirm both candidates beyond any doubt. We find redshifts of z=6.541 and z=6.604 for MASOSA and CR7, respectively. MASOSA has a strong detection in Ly$\alpha$ with a line width of $386\pm30$ km/s (FWHM) and with high EW$_0$ (>200 \AA), but it is undetected in the continuum. CR7, with an observed Ly$\alpha$ luminosity of $10^{43.93\pm0.05}$erg/s is the most luminous Ly$\alpha$ emitter ever found at z>6. CR7 reveals a narrow Ly$\alpha$ line with $266\pm15$ km/s FWHM, being detected in the NIR (rest-frame UV, with $\beta=-2.3\pm0.1$) with an excess in $J$, and also strongly detected in IRAC/Spitzer. We detect a narrow HeII1640$\AA$ emission line ($6\sigma$) which explains the excess seen in the $J$ band photometry (EW$_0$~80 \AA). We find no other emission lines from the UV to the NIR in our X-SHOOTER spectra, nor any signatures of Wolf-Rayet (WR) stars. We find that CR7 is best explained by a combination of a PopIII-like population which dominates the rest-frame UV and the nebular emission, and a more normal stellar population which dominates the mass. HST/WFC3 observations show that the light is indeed spatially separated between a very blue component, coincident with Ly$\alpha$ and HeII emission, and two red components (~5 kpc away), which dominate the mass. Our findings are consistent with theoretical predictions of a PopIII wave, with PopIII star formation migrating away from the original sites of star formation.

/pdf/evidence-for-popiii-like-stellar-populations-in-the-most-3boy304rut.pdf

Evidence for PopIII-like Stellar Populations in the Most Luminous Lyman-α Emitters at the Epoch of Reionization: Spectroscopic Confirmation

Early galaxy formation and its large-scale effects

We present Hα maps at 1 kpc spatial resolution for star-forming galaxies at z ~ 1, made possible by the Wide Field Camera 3 grism on Hubble Space Telescope (HST). Employing this capability over all five 3D-HST/CANDELS fields provides a sample of 3200 galaxies enabling a division into subsamples based on stellar mass and star formation rate (SFR). By creating deep stacked Hα images, we reach surface brightness limits of 1 × 10^(−18) erg s^(−1) cm^(−2) arcsec^(−2), allowing us to map the distribution of ionized gas to ~10 kpc for typical L* galaxies at this epoch. We find that the spatial extent of the Hα distribution increases with stellar mass as r_(Hα) = 1.5(M⋆/10^(10) M⊙)^(0.23) kpc. The Hα emission is more extended than the stellar continuum emission, consistent with inside-out assembly of galactic disks. This effect grows stronger with mass as r_(Hα)/r⋆ = 1.1 (M⋆/10^(10) M⊙)^(0.054). We map the Hα distribution as a function of SFR(IR+UV) and find evidence for "coherent star formation" across the SFR–M * plane: above the main sequence (MS), Hα is enhanced at all radii; below the MS, Hα is depressed at all radii. This suggests that at all masses the physical processes driving the enhancement or suppression of star formation act throughout the disks of galaxies. At high masses (10^(10.5) < M⋆/M⊙ < 10^(11)), above the MS, Hα is particularly enhanced in the center, potentially building bulges and/or supermassive black holes. Below the MS, a strong central dip in the EW(Hα), as well as the inferred specific SFR, appears. Importantly, though, across the entirety of the SFR–M* plane, the absolute SFR as traced by Hα is always centrally peaked, even in galaxies below the MS.

/pdf/where-stars-form-inside-out-growth-and-coherent-star-19trnx2wb9.pdf

Where stars form: inside-out growth and coherent star formation from HST Hα maps of 3200 galaxies across the main sequence at 0.7 < z < 1.5

Using wide-field narrow-band surveys, we provide a new measurement of the z = 6.6 Lymanα 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 ~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 Lyα LF between z = 5.7 and 6.6, which is supported by spectroscopic follow-up, and conclude that sources with Himiko-like luminosity are not as rare as previously thought, with number densities of ~1.5 × 10 -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 observed faint and bright LAEs, overcoming cosmic variance. This differential evolution is also seen in the spectroscopic follow-up of UV-selected galaxies and is now also confirmed for LAEs, and we argue that it may be an effect of reionization. Using a toy model, we show that such differential evolution of the LF is expected, since brighter sources are able to ionize their surroundings earlier, such that Lyα 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 reionization process.

/pdf/identification-of-the-brightest-lya-emitters-at-z-6-6-58wdhbtixl.pdf

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

The KMOS Redshift One Spectroscopic Survey (KROSS) is an ESO guaranteed time survey of 795 typical star-forming galaxies in the redshift range z=0.8-1.0 with the KMOS instrument on the VLT. In this paper we present resolved kinematics and star formation rates for 584 z~1 galaxies. This constitutes the largest near-infrared Integral Field Unit survey of galaxies at z~1 to date. We demonstrate the success of our selection criteria with 90% of our targets found to be Halpha emitters, of which 81% are spatially resolved. The fraction of the resolved KROSS sample with dynamics dominated by ordered rotation is found to be 83$\pm$5%. However, when compared with local samples these are turbulent discs with high gas to baryonic mass fractions, ~35%, and the majority are consistent with being marginally unstable (Toomre Q~1). There is no strong correlation between galaxy averaged velocity dispersion and the total star formation rate, suggesting that feedback from star formation is not the origin of the elevated turbulence. We postulate that it is the ubiquity of high (likely molecular) gas fractions and the associated gravitational instabilities that drive the elevated star-formation rates in these typical z~1 galaxies, leading to the ten-fold enhanced star-formation rate density. Finally, by comparing the gas masses obtained from inverting the star-formation law with the dynamical and stellar masses, we infer an average dark matter to total mass fraction within 2.2$r_e$ (9.5kpc) of 65$\pm$12%, in agreement with the results from hydrodynamic simulations of galaxy formation.

/pdf/the-kmos-redshift-one-spectroscopic-survey-kross-dynamical-2gxw7w0o0r.pdf

The KMOS Redshift One Spectroscopic Survey (KROSS):dynamical properties, gas and dark matter fractions of typical z~1 star-forming galaxies

We present results from the largest contiguous narrow-band survey in the near-infrared. We have used WIRCam/CFHT and the lowOH2 filter (1.187$\pm$0.005 \mu m) to survey ~10 deg$^2$ of contiguous extragalactic sky in the SA22 field. A total of ~6000 candidate emission-line galaxies are found. We use deep CFHTLS $ugriz$ and UKIDSS DXS $J$ and $K$ data to obtain robust photometric redshifts. We combine our data with HiZELS (COSMOS+UDS) and explore VVDS, VIPERS, KMOS and obtain our own spectroscopic follow-up with FMOS and MOSFIRE to derive large samples of high-redshift emission-line selected galaxies: 3471 H\alpha\ emitters at z=0.8, 1343 [OIII]+H\beta\ emitters at z=1.4 and 572 [OII] emitters at z=2.2. We probe co-moving volumes of >10$^6$ Mpc$^3$ and find significant over-densities, including an 8.5\sigma\ (spectroscopically confirmed) over-density of H\alpha\ emitters at z=0.81. We derive H\alpha, [OIII]+H\beta\ and [OII] luminosity functions at z=0.8, 1.4 and 2.2, respectively, and present implications for future surveys such as EUCLID. Our uniquely large volumes/areas allow us to sub-divide the samples in thousands of randomised combinations of areas and provide a robust empirical measurement of sample/cosmic variance. We show that surveys for star-forming/emission-line galaxies at a depth similar to ours can only overcome cosmic-variance (errors 5x10$^5$ Mpc$^3$; errors on L$^*$ and \Phi$^*$ due to sample (cosmic) variance on surveys probing ~10${^4}$ Mpc$^3$ and ~10$^5$ Mpc$^3$ are typically very high: ~300% and ~40-60%, respectively.

/pdf/cf-hizels-an-10-deg2-emission-line-survey-with-spectroscopic-42e74iacxr.pdf

CF-HiZELS, an ~ 10 deg2 emission-line survey with spectroscopic follow-up : Hα, [O III] + Hβ and [O II] luminosity functions at z = 0.8, 1.4 and 2.2

Candidate galaxies at redshifts of z ~ 10 are now being found in extremely deep surveys, probing very small areas. As a consequence, candidates are very faint, making spectroscopic confirmation practically impossible. In order to overcome such limitations, we have undertaken the CF-HiZELS survey, which is a large-area, medium-depth near-infrared narrow-band survey targeted at z = 8.8 Lyman α (Lyα) emitters (LAEs) and covering 10 deg2 in part of the SSA22 field with the Canada-France-Hawaii Telescope (CFHT). We surveyed a comoving volume of 4.7 × 106 Mpc3 to a Lyα luminosity limit of 6.3 × 1043 erg s-1. We look for Lyα candidates by applying the following criteria: (i) clear emission-line source, (ii) no optical detections (ugriz from CFHTLS), (iii) no visible detection in the optical stack (ugriz > 27), (iv) visually checked reliable NBJ and J detections and (v) J - K ≤ 0. We compute photometric redshifts and remove a significant amount of dusty lower redshift line-emitters at z ~ 1.4 or 2.2. A total of 13 Lyα candidates were found, of which two are marked as strong candidates, but the majority have very weak constraints on their spectral energy distributions. Using follow-up observations with SINFONI/VLT, we are able to exclude the most robust candidates as LAEs. We put a strong constraint on the Lyα luminosity function at z ~ 9 and make realistic predictions for ongoing and future surveys. Our results show that surveys for the highest redshift LAEs are susceptible of multiple contaminations and that spectroscopic follow-up is absolutely necessary.

/pdf/a-10-deg2-lyman-a-survey-at-z-8-8-with-spectroscopic-follow-1xeyjmbrig.pdf

A 10 deg2 Lyman α survey at z=8.8 with spectroscopic follow-up: strong constraints on the luminosity function and implications for other surveys

We present results from the largest contiguous narrow-band survey in the near-infrared We have used WIRCam/CFHT and the lowOH2 filter (1187$\pm$0005 $\mu$m) to survey ~10 deg$^2$ of contiguous extragalactic sky in the SA22 field A total of ~6000 candidate emission-line galaxies are found We use deep ugrizJK data to obtain robust photometric redshifts We combine our data with the High-redshift Emission Line Survey (HiZELS), explore spectroscopic surveys (VVDS, VIPERS) and obtain our own spectroscopic follow-up with KMOS, FMOS and MOSFIRE to derive large samples of high-redshift emission-line selected galaxies: 3471 H$\alpha$ emitters at z=08, 1343 [OIII]+H$\beta$ emitters at z=14 and 572 [OII] emitters at z=22 We probe co-moving volumes of >10$^6$ Mpc$^3$ and find significant over-densities, including an 85$\sigma$ (spectroscopically confirmed) over-density of H$\alpha$ emitters at z=081 We derive H$\alpha$, [OIII]+H$\beta$ and [OII] luminosity functions at z=08,14,22, respectively, and present implications for future surveys such as Euclid Our uniquely large volumes/areas allow us to sub-divide the samples in thousands of randomised combinations of areas and provide a robust empirical measurement of sample/cosmic variance We show that surveys for star-forming/emission-line galaxies at a depth similar to ours can only overcome cosmic-variance (errors 5x10$^{5}$ Mpc$^{3}$; errors on $L^*$ and $\phi^*$ due to sample (cosmic) variance on surveys probing ~10$^4$ Mpc$^{3}$ and ~10$^5$ Mpc$^{3}$ are typically very high: ~300% and ~40-60%, respectively

CF-HiZELS, a 10 deg$^2$ emission-line survey with spectroscopic follow-up: H\alpha, [OIII]+H\beta\ and [OII] luminosity functions at z=0.8, 1.4 and 2.2

Jae-Woo Kim

Papers

CF-HiZELS, an ~ 10 deg2 emission-line survey with spectroscopic follow-up : Hα, [O III] + Hβ and [O II] luminosity functions at z = 0.8, 1.4 and 2.2

A 10 deg2 Lyman α survey at z=8.8 with spectroscopic follow-up: strong constraints on the luminosity function and implications for other surveys

CF-HiZELS, a 10 deg$^2$ emission-line survey with spectroscopic follow-up: H\alpha, [OIII]+H\beta\ and [OII] luminosity functions at z=0.8, 1.4 and 2.2