We present Lyα luminosity function (LF), clustering measurements, and Lyα line profiles based on the largest sample, to date, of 207 Lyα emitters (LAEs) at z = 6.6 on the 1-deg 2 sky of Subaru/XMM-Newton Deep Survey (SXDS) field. Our z = 6.6 Lyα LF including cosmic variance estimates yields the best-fit Schechter parameters of φ * = 8.5 +3.0 −2.2 × 10 −4 Mpc −3 and L * Lyα = 4.4 +0.6 −0.6 × 10 42 erg s −1 with a fixed α = −1.5, and indicates a decrease from z = 5.7 at the 90% confidence level. However, this decrease is not large, only ≃ 30% in Lyα luminosity, which is too small to be identified in the previous studies. A clustering signal of z = 6.6 LAEs is detected for the first time. We obtain the correlation length of r 0 = 2 − 5 h −1 100 Mpc and bias of b = 3 − 6, and find no significant boost of clustering amplitude by reionization at z = 6.6. The average hosting dark halo mass inferred from clustering is 10 10 − 10 11 M ⊙ , and duty cycle of LAE population is roughly ∼ 1% albeit with large uncertainties. The average of our high-quality Keck/DEIMOS spectra shows an FWHM velocity width of 251 ± 16km s −1 . We find no large evolution of Lyα line profile from z = 5.7 to 6.6, and no anti-correlation between Lyα luminosity and line width at z = 6.6. The combination of various reionization models and our observational results about the LF, clustering, and line profile indicates that there would exist a small decrease of IGM's Lyα transmission owing to reionization, but that the hydrogen IGM is not highly neutral at z = 6.6. Our neutral-hydrogen fraction constraint implies that the major reionization process took place at z 7.

Understanding cosmic reionization requires the identification and characterization of early sources of hydrogenionizing photons. The 2012 Hubble Ultra Deep Field (UDF12) campaign has acquired the deepest infrared images with the Wide Field Camera 3 aboard Hubble Space Telescope and, for the first time, systematically explored the galaxy population deep into the era when cosmic microwave background (CMB) data indicate reionization was underway. The UDF12 campaign thus provides the best constraints to date on the abundance, luminosity distribution, and spectral properties of early star-forming galaxies. We synthesize the new UDF12 results with the most recent constraints from CMB observations to infer redshift-dependent ultraviolet (UV) luminosity densities, reionization histories, and electron scattering optical depth evolution consistent with the available data. Under reasonable assumptions about the escape fraction of hydrogen-ionizing photons and the intergalactic medium clumping factor, we find that to fully reionize the universe by redshift z ∼ 6 the population of star-forming galaxies at redshifts z ∼ 7-9 likely must extend in luminosity below the UDF12 limits to absolute UV magnitudes of M UV ∼ −13 or fainter. Moreover, low levels of star formation extending to redshifts z ∼ 15-25, as suggested by the normal UV colors of z 7-8 galaxies and the smooth decline in abundance with redshift observed by UDF12 to z 10, are additionally likely required to reproduce the optical depth to electron scattering inferred from CMB observations.

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Hyper Suprime-Cam (HSC) is a wide-field imaging camera on the prime focus of the 8.2m Subaru telescope on the summit of Maunakea in Hawaii. A team of scientists from Japan, Taiwan and Princeton University is using HSC to carry out a 300-night multi-band imaging survey of the high-latitude sky. The survey includes three layers: the Wide layer will cover 1400 deg 2 in five broad bands (grizy), with a 5 σ point-source depth of r ≈ 26. The Deep layer covers a total of 26 deg 2 in four fields, going roughly a magnitude fainter, while the UltraDeep layer goes almost a magnitude fainter still in two pointings of HSC (a total of 3.5 deg 2). Here we describe the instrument, the science goals of the survey, and the survey strategy and data processing. This paper serves as an introduction to a special issue of the Publications of the Astronomical Society of Japan, which includes a large number of technical and scientific papers describing results from the early phases of this survey.

We present the results of the deepest search to date for star-forming galaxies beyond a redshift z ≃8.5 utilizing a new sequence of near-infrared Wide Field Camera 3 images of the Hubble Ultra Deep Field. This 'UDF12' campaign completed in September 2012 doubles the earlier exposures with WFC3/IR in this field and quadruples the exposure in the key F105W filter used to locate such distant galaxies. Combined with additional imaging in the F140W filter, the fidelity of high redshift candidates is greatly improved. Using spectral energy distribution fitting techniques on objects selected from a deep multi-band near-infrared stack we find 7 promising z >8.5 candidates. As none of the previously claimed UDF candidates with 8.5 < z <10 is confirmed by our deeper multi-band imaging, our campaign has transformed the measured abundance of galaxies in this redshift range. Although we recover the candidate UDFj-39546284 (previously proposed at z=10.3), it is undetected in the newly added F140W image, implying it lies at z=11.9 or is an intense emission line galaxy at z ≃ 2.4. Although no physically-plausible model can explain the required line intensity given the lack of Lyman α or broad-band UV signal, without an infrared spectrum we cannot rule out an exotic interloper. Regardless, our robust z ≃ 8.5 − 10 sample demonstrates a luminosity density that continues the smooth decline observed over 6 < z < 8. Such continuity has important implications for models of cosmic reionization and future searches for z >10 galaxies with JWST.

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We present results of our large area survey for z -band dropout galaxies at z = 7 in a 1568 arcmin 2 sky area covering the SDF and GOODS-N fields. Combining our ultra-deep Subaru/Suprime-Cam z -and y-band (λ eff = 1 μm) images with legacy data of Subaru and Hubble Space Telescope, we have identified 22 bright z-dropout galaxies down to y = 26, one of which has a spectroscopic redshift of z = 6.96 determined from Lyα emission. The z = 7 luminosity function yields the best-fit Schechter parameters of φ * = 0.69 +2.62 −0.55 × 10 −3 Mpc −3 , M * UV = −20.10 ± 0.76 mag, and α = −1.72 ± 0.65, and indicates a decrease from z = 6 at a > 95% confidence level. This decrease is beyond the cosmic variance in our two fields, which is estimated to be a factor of 2. We have found that the cosmic star formation rate density drops from the peak at z = 2-3 to z = 7 roughly by a factor of ∼10 but not larger than ∼100. A comparison with the reionization models suggests either that the universe could not be totally ionized by only galaxies at z = 7, or more likely that properties of galaxies at z = 7 are different from those at low redshifts having, e.g., a larger escape fraction ( 0.2), a lower metallicity, and/or a flatter initial mass function. Our SDF z-dropout galaxies appear to form 60 Mpc long filamentary structures, and the z = 6.96 galaxy with Lyα emission is located at the center of an overdense region consisting of four UV bright dropout candidates, which might suggest an existence of a well-developed ionized bubble at z = 7.

We present our new Atacama Large Millimeter/Submillimeter Array (ALMA) observations targeting [O iii]88 μm, [C ii]158 μm, [N ii]122 μm, and dust-continuum emission for three Lyman break galaxies at z = 6.0293–6.2037, identified in the Subaru/Hyper Suprime-Cam survey. We clearly detect [O iii] and [C ii] lines from all of the galaxies at 4.3–11.8σ levels, and identify multi-band dust-continuum emission in two of the three galaxies, allowing us to estimate infrared luminosities and dust temperatures simultaneously. In conjunction with previous ALMA observations for six galaxies at z > 6, we confirm that all the nine z = 6–9 galaxies have high [O iii]/[C ii] ratios of , ∼10 times higher than z ∼ 0 galaxies. We also find a positive correlation between the [O iii]/[C ii] ratio and the Lyα equivalent width (EW) at the ∼90% significance level. We carefully investigate physical origins of the high [O iii]/[C ii] ratios at z = 6–9 using Cloudy, and find that high density of the interstellar medium, low C/O abundance ratio, and the cosmic microwave background attenuation are responsible to only a part of the z = 6–9 galaxies. Instead, the observed high [O iii]/[C ii] ratios are explained by 10–100 times higher ionization parameters or low photodissociation region (PDR) covering fractions of 0%–10%, both of which are consistent with our [N ii] observations. The latter scenario can be reproduced with a density-bounded nebula with PDR deficit, which would enhance the Lyα, Lyman continuum, and ionizing photons escape from galaxies, consistent with the [O iii]/[C ii]-Lyα EW correlation we find.