Search

We present an unprecedentedly large catalog consisting of 2230 ≳ L* Lyα emitters (LAEs) at z = 5.7 and 6.6 on the 13.8 and 21.2deg2 sky, respectively, that are identified by the SILVERRUSH program with the first narrow-band imaging data of the Hyper Suprime-Cam (HSC) survey. We confirm that the LAE catalog is reliable on the basis of 96 LAEs whose spectroscopic redshifts are already determined by this program and previous studies. This catalogue is also available online. Based on this catalogue, we derive the rest-frame Lyα equivalent-width distributions of LAEs at z ≃ 5.7~6.6 that are reasonably explained by the exponential profiles with scale lengths of ≃ 120~170Å, showing no significant evolution from z ≃ 5.7 to z ≃ 6.6. We find that 275 LAEs with large equivalent widths (LEWs) of >240Å are candidates of young metal poor galaxies and AGNs. We also find that the fraction of LEW LAEs to all LAEs is 4% and 21% at z ≃ 5.7 and z ~ 6.6, respectively. Our LAE catalog includes 11 Lyα blobs (LABs) that are LAEs with spatially extended Lyα emission with a profile that is clearly distinguished from those of stellar objects at the ≳3σ level. The number density of the LABs at z = 6~7 is ~10~7~10~6Mpc~3, being ~10~100 times lower than those claimed for LABs at z ≃ 2~3, suggestive of disappearing LABs at z ≳ 6, albeit with the different selection methods and criteria for the low and high-z LABs. [ABSTRACT FROM AUTHOR]

We present Lyα and UV-nebular emission line properties of bright Lyα emitters (LAEs) at z = 6-7 with a luminosity of log LLyα/[erg s-1] = 43-44 identified in the 21 deg2 area of the SILVERRUSH early sample developed with the Subaru Hyper Suprime-Cam survey data. Our optical spectroscopy newly confirms 21 bright LAEs with clear Lyα emission, and contributes to making a spectroscopic sample of 96 LAEs at z = 6-7 in SILVERRUSH. From the spectroscopic sample, we select seven remarkable LAEs as bright as Himiko and CR7 objects, and perform deep Keck/MOSFIRE and Subaru/nuMOIRCS near-infrared spectroscopy reaching the 3 σ flux limit of ~2 × 10-18 erg s-1 for the UV-nebular emission lines of He II λ1640, C IV λλ1548,1550, and O III]λλ1661,1666. Except for one tentative detection of C IV, we find no strong UV-nebular lines down to the flux limit, placing the upper limits of the rest-frame equivalent widths (EW0) of ~2-4 Å for C IV, He II, and O III] lines. We also investigate the VLT/X-SHOOTER spectrum of CR7 whose 6 σ detection of He II is claimed by Sobral et al. Although two individuals and the ESO archive service carefully reanalyzed the X-SHOOTER data that are used in the study of Sobral et al., no He II signal of CR7 is detected, supportive of weak UV-nebular lines of the bright LAEs even for CR7. The spectral properties of these bright LAEs are thus clearly different from those of faint dropouts at z ~ 7 that have strong UV-nebular lines shown in the various studies. Comparing these bright LAEs and the faint dropouts, we find anti-correlations between the UV-nebular line EW0 and the UV-continuum luminosity, which are similar to those found at z ~ 2-3. [ABSTRACT FROM AUTHOR]

We present the redshift evolution of the radial surface brightness profile of the rest-frame UV and optical stellar continua for 9119 Lyα emitters (LAEs) at z ≃ 0–8 and 0–2, respectively. Using Hubble Space Telescope data and the LAE catalogs taken from the literature, we derive the structural quantities of the 9119 LAEs, and of ≃180,000 of photo-z star-forming galaxies (SFGs) and Lyman break galaxies (LBGs) for comparison, by the well-tested profile fitting. From 936 well-fitted LAEs, we carefully define a homogeneous sample of LAEs falling in the same ranges of UV-continuum luminosity and Lyα equivalent width over z ≃ 0–8, and evaluate the redshift evolution. We find that the distribution of effective radius re is represented by a log-normal function, and that the median Sérsic index is almost constant at n ≃ 1–1.5 for the LAEs over z ≃ 0–7, suggesting that typical LAEs have a stellar-disk morphology. The size–luminosity relation of the LAEs decreases monotonically toward high z, following size–luminosity relations of SFGs and LBGs. The median re values of the LAEs evolve significantly as re ∝ (1 + z)−1.37, similar to those of the SFGs and LBGs in the same luminosity range, in contrast with the claims of no evolution made by previous studies, whose LAE samples are probably biased to faint sources at low z. The re distribution, star formation rate surface densities, and stellar-to-halo size ratios of the LAEs are comparable with those of the SFGs and LBGs, indicating that LAEs have stellar components similar to SFGs and LBGs with a Lyα emissivity controlled by non-stellar physics such as the geometry, kinematics, and ionization states of the interstellar/circumgalactic medium. [ABSTRACT FROM AUTHOR]

We present spatial correlations of galaxies and IGM neutral hydrogen H i in the COSMOS/UltraVISTA 1.62 deg2 field. Our data consist of 13,415 photo-z galaxies at z ∼ 2–3 with and the Lyα forest absorption lines in the background quasar spectra selected from SDSS data with no signature of damped Lyα system contamination. We estimate a galaxy overdensity δgal in an impact parameter of 2.5 (proper) Mpc, and calculate the Lyα forest fluctuations whose negative values correspond to the strong Lyα forest absorption lines. We identify weak evidence of an anti-correlation between δgal and with a Spearman’s rank correlation coefficient of −0.39 suggesting that the galaxy overdensities and the Lyα forest absorption lines positively correlate in space at the ∼90% confidence level. This positive correlation indicates that high-z galaxies exist around an excess of H i gas in the Lyα forest. We find four cosmic volumes, dubbed Aobs, Bobs, Cobs, and Dobs, that have extremely large (small) values of δgal ≃ 0.8 (−1) and , three of which, Bobs–Dobs, significantly depart from the δgal– correlation, and weaken the correlation signal. We perform cosmological hydrodynamical simulations and compare with our observational results. Our simulations reproduce the δgal– correlation, agreeing with the observational results. Moreover, our simulations have model counterparts of Aobs–Dobs, and suggest that the observations pinpoint, by chance, a galaxy overdensity like a proto-cluster, gas filaments lying on the quasar sightline, a large void, and orthogonal low-density filaments. Our simulations indicate that the significant departures of Bobs–Dobs are produced by the filamentary large-scale structures and the observation sightline effects. [ABSTRACT FROM AUTHOR]

We investigate the evolution of clumpy galaxies with Hubble Space Telescope (HST) samples of ∼17,000 photo-z and Lyman break galaxies at z ≃ 0–8. We detect clumpy galaxies with off-center clumps in a self-consistent algorithm that is well tested with previous study results, and we measure the number fraction of clumpy galaxies at the rest-frame UV, . We identify an evolutionary trend of over z ≃ 0–8 for the first time: increases from z ≃ 8 to z ≃ 1–3 and subsequently decreases from z ≃ 1 to z ≃ 0, which follows the trend of the Madau–Lilly plot. A low average Sérsic index of n ≃ 1 is found in the underlining components of our clumpy galaxies at z ≃ 0–2, indicating that typical clumpy galaxies have disk-like surface brightness profiles. Our values correlate with physical quantities related to star formation activities for star-forming galaxies at z ≃ 0–7. We find that clump colors tend to be red at a small galactocentric distance for massive galaxies with . All of these results are consistent with the picture that a majority of clumps form in the violent disk instability and migrate into the galactic centers. [ABSTRACT FROM AUTHOR]

We present the SILVERRUSH program strategy and clustering properties investigated with ∼2,000 Lyα emitters at z=5.7 and 6.6 found in the early data of the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey exploiting the carefully designed narrowband filters. We derive angular correlation functions with the unprecedentedly large samples of LAEs at z=6−7 over the large total area of 14−21 deg2 corresponding to 0.3−0.5 comoving Gpc2. We obtain the average large-scale bias values of bavg=4.1±0.2 (4.5±0.6) at z=5.7 (z=6.6) for ≳L∗ LAEs, indicating the weak evolution of LAE clustering from z=5.7 to 6.6. We compare the LAE clustering results with two independent theoretical models that suggest an increase of an LAE clustering signal by the patchy ionized bubbles at the epoch of reionization (EoR), and estimate the neutral hydrogen fraction to be xHI=0.15+0.15−0.15 at z=6.6. Based on the halo occupation distribution models, we find that the ≳L∗ LAEs are hosted by the dark-matter halos with the average mass of log(⟨Mh⟩/M⊙)=11.1+0.2−0.4 (10.8+0.3−0.5) at z=5.7 (6.6) with a Lyα duty cycle of 1 % or less, where the results of z=6.6 LAEs may be slightly biased, due to the increase of the clustering signal at the EoR. Our clustering analysis reveals the low-mass nature of ≳L∗ LAEs at z=6−7, and that these LAEs probably evolve into massive super-L∗ galaxies in the present-day universe. [ABSTRACT FROM AUTHOR]

We present evidence that a region of high effective Lyα optical depth at z ∼ 5.7 is associated with an underdense region at the tail end of cosmic reionization. We carried out a survey of Lyman-break Galaxies (LBGs) using Subaru Hyper Suprime-Cam in the field of the z = 5.98 quasar J0148+0600, whose spectrum presents an unusually long (∼160 cMpc) and opaque (τ ≳ 7) Lyα trough at 5.5 ≤ z ≤ 5.9. LBG candidates were selected to lie within the redshift range of the trough, and the projected number densities were measured within 90 cMpc of the quasar sightline. The region within 8′ (or ≈19 cMpc) of the quasar position is the most underdense of the whole field. The significance of the presence of the void is estimated to be 99%. This is consistent with the significant deficit of Lyα emitters (LAEs) at z = 5.72 reported by Becker et al. and suggests that the paucity of LAEs is not purely due to the removal of the Lyα emission by the high opacity but reflects a real coherent underdensity of galaxies across the entire redshift range of the trough. These observations are consistent with scenarios in which large optical depth fluctuations arise due to fluctuations in the galaxy-dominant UV background or due to residual neutral islands that are expected from reionization that is completed at redshifts as low as z ≲ 5.5. [ABSTRACT FROM AUTHOR]

We investigate Lyα, [O iii] λ5007, Hα, and [C ii] 158 μm emission from 1124 galaxies at z = 4.9–7.0. Our sample is composed of 1092 Lyα emitters (LAEs) at z = 4.9, 5.7, 6.6, and 7.0 identified by Subaru/Hyper-Suprime-Cam (HSC) narrowband surveys covered by Spitzer Large Area Survey with Hyper-Suprime-Cam (SPLASH) and 34 galaxies at z = 5.148–7.508 with deep ALMA [C ii] 158 μm data in the literature. Fluxes of strong rest-frame optical lines of [O iii] and Hα (Hβ) are constrained by significant excesses found in the SPLASH 3.6 and 4.5 μm photometry. At z = 4.9, we find that the rest-frame Hα equivalent width and the Lyα escape fraction fLyα positively correlate with the rest-frame Lyα equivalent width . The correlation is similarly found at z ∼ 0–2, suggesting no evolution of the correlation over z ≃ 0–5. The typical ionizing photon production efficiency of LAEs is log(ξion/[Hz erg−1]) ≃ 25.5, significantly (60%–100%) higher than those of LBGs at a given UV magnitude. At z = 5.7–7.0, there exists an interesting turnover trend that the [O iii]/Hα flux ratio increases in and then decreases out to . We also identify an anticorrelation between a ratio of [C ii] luminosity to star formation rate (L[C ii]/SFR) and at the >99% confidence level.. We carefully investigate physical origins of the correlations with stellar-synthesis and photoionization models and find that a simple anticorrelation between and metallicity explains self-consistently all of the correlations of Lyα, Hα, [O iii]/Hα, and [C ii] identified in our study, indicating detections of metal-poor (∼0.03 Z⊙) galaxies with . [ABSTRACT FROM AUTHOR]

The survey of Lyman α emitters (LAEs) with the Subaru Hyper Suprime-Cam, called SILVERRUSH (Ouchi et al. 2018, PASJ, 70, S13), is producing massive data of LAEs at z ≳ 6. Here we present LAE simulations to compare the SILVERRUSH data. In 162³ comoving Mpc³ boxes, where numerical radiative transfer calculations of reionization were performed, LAEs have been modeled with physically motivated analytic recipes as a function of halo mass. We have examined 2³ models depending on the presence or absence of dispersion of halo Lyα emissivity, dispersion of the halo Lyα optical depth, τα, and halo mass dependence of τα. The unique free parameter in our model, a pivot value of τα, is calibrated so as to reproduce the z = 5.7 Lyα luminosity function (LF) of SILVERRUSH. We compare our model predictions with Lyα LFs at z = 6.6 and 7.3, LAE angular auto-correlation functions (ACFs) at z = 5.7 and 6.6, and LAE fractions in Lyman break galaxies at 5 < z < 7. The Lyα LFs and ACFs are reproduced by multiple models, but the LAE fraction turns out to be the most critical test. The dispersion of τα and the halo mass dependence of τα are essential to explain all observations reasonably. Therefore, a simple model of one-to-one correspondence between halo mass and Lyα luminosity with a constant Lyα escape fraction has been ruled out. Based on our best model, we present a formula to estimate the intergalactic neutral hydrogen fraction, xHI, from the observed Lyα luminosity density at z ≳ 6. We finally obtain xHI = 0.5-0.3+0.1 as a volume-average at z = 7.3. [ABSTRACT FROM AUTHOR]

We present the large statistics of the galaxy effective radius Re in the rest-frame far-infrared (FIR) wavelength obtained from 1627 Atacama Large Millimeter/submillimeter Array (ALMA) 1 mm band maps that become public by 2017 July. Our ALMA sample consists of 1034 sources with the star formation rate and the stellar mass at z = 0–6. We homogeneously derive and FIR luminosity LFIR of our ALMA sources via the uv-visibility method with the exponential disk model, carefully evaluating selection and measurement incompletenesses by realistic Monte-Carlo simulations. We find that there is a positive correlation between and LFIR at the >99% significance level. The best-fit power-law function, , provides , and shows that at a fixed LFIR decreases toward high redshifts. The best-fit α and the redshift evolution of are similar to those of Re in the rest-frame UV (optical) wavelength () revealed by Hubble Space Telescope (HST) studies. We identify that our ALMA sources have significant trends of and , which suggests that the dusty starbursts take place in compact regions. Moreover, of our ALMA sources is comparable to of quiescent galaxies at z ∼ 1–3 as a function of stellar mass, supporting the evolutionary connection between these two galaxy populations. We also investigate rest-frame UV and optical morphologies of our ALMA sources with deep HST images, and find that ∼30%–40% of our ALMA sources are classified as major mergers. This indicates that dusty starbursts are triggered by not only the major mergers but also the other mechanism(s). [ABSTRACT FROM AUTHOR]

We study the UV luminosity functions (LFs) at z ~ 4, 5, 6, and 7 based on the deep large-area optical images taken by the Hyper Suprime-Cam (HSC) Subaru Strategic Program (SSP). On the 100 deg2 sky of the HSC SSP data available to date, we take enormous samples consisting of a total of 579565 dropout candidates at z ~ 4-7 by the standard color selection technique, 358 out of which are spectroscopically confirmed by our follow-up spectroscopy and other studies. We obtain UV LFs at z ~ 4-7 that span a very wide UV luminosity range of ~0.002-100 L*UV (-26 < MUV < -14 mag) by combining LFs from our program and the ultra-deep Hubble Space Telescope legacy surveys. We derive three parameters of the best-fit Schechter function, ϕ*, M*UV , and α, of the UV LFs in the magnitude range where the active galactic nucleus (AGN) contribution is negligible, and find that α and ϕ* decrease from z ~ 4 to 7 with no significant evolution of M*UV . Because our HSC SSP data bridge the LFs of galaxies and AGNs with great statistical accuracy, we carefully investigate the bright end of the galaxy UV LFs that are estimated by the subtraction of the AGN contribution either aided by spectroscopy or the best-fit AGN UV LFs. We find that the bright end of the galaxy UV LFs cannot be explained by the Schechter function fits at >2 σ significance, and require either double power-law functions or modified Schechter functions that consider a magnification bias due to gravitational lensing. [ABSTRACT FROM AUTHOR]

We present clustering properties from 579492 Lyman-break galaxies (LBGs) at z ~ 4-6 over the 100 deg2 sky (corresponding to a 1.4 Gpc3 volume) identified in early data of the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. We derive angular correlation functions (ACFs) for the HSC LBGs with unprecedentedly high statistical accuracies at z ~ 4-6, and compare them with the halo occupation distribution (HOD) models. We clearly identify significant ACF excesses in 10" < θ < 90", the transition scale between one- and two-halo terms, suggestive of the existence of the non-linear halo bias effect. Combining the HOD models and previous clustering measurements of faint LBGs at z ~ 4-7, we investigate the dark matter halo mass (Mh) of the z ~ 4-7 LBGs and its correlation with various physical properties including the star formation rate (SFR), the stellar-to-halo mass ratio (SHMR), and the dark matter accretion rate (M˙h) over a wide mass range of Mh/M⊙ = 4 × 1010-4 × 1012. We find that the SHMR increases from z ~ 4 to 7 by a factor of ~4 at Mh ≃ 1 × 1011M⊙ , while the SHMR shows no strong evolution in the similar redshift range at Mh ≃ 1 × 1012M⊙ . Interestingly, we identify a tight relation of SFR/M˙h-Mh showing no significant evolution beyond 0.15 dex in this wide mass range over z ~ 4-7. This weak evolution suggests that the SFR/M˙h-Mh relation is a fundamental relation in high-redshift galaxy formation whose star formation activities are regulated by the dark matter mass assembly. Assuming this fundamental relation, we calculate the cosmic star formation rate densities (SFRDs) over z = 0-10 (a.k.a. the Madau-Lilly plot). The cosmic SFRD evolution based on the fundamental relation agrees with the one obtained by observations, suggesting that the cosmic SFRD increase from z ~ 10 to 4 - 2 (decrease from z ~ 4-2 to 0) is mainly driven by the increase of the halo abundance (the decrease of the accretion rate). [ABSTRACT FROM AUTHOR]

We present initial results from the Subaru Strategic Program (SSP) with Hyper Suprime-Cam (HSC) on a comprehensive survey of emission-line galaxies at z < 1.5 based on narrowband imaging. The first Public Data Release provides us with data from two narrowband filters, specifically NB816 and NB921 over 5.7 deg2 and 16.2 deg2 respectively. The 5 σ limiting magnitudes are 25.2 mag (UltraDeep layer, 1.4 deg2) and 24.8 mag (Deep layer, 4.3 deg2) for NB816, and 25.1 mag (UltraDeep, 2.9 deg2) and 24.6-24.8 mag (Deep, 13.3 deg2) for NB921. The wide-field imaging allows us to construct unprecedentedly large samples of 8054 H α emitters at z ≈ 0.25 and 0.40, 8656 [O III] emitters at z ≈ 0.63 and 0.84, and 16877 [O II] emitters at z ≈ 1.19 and 1.47. We map the cosmic web on scales out to about 50 comoving Mpc that includes galaxy clusters, identified by red sequence galaxies, located at the intersection of filamentary structures of star-forming galaxies. The luminosity functions of emission-line galaxies are measured with precision and are consistent with published studies. The wide field coverage of the data enables us to measure the luminosity functions up to brighter luminosities than previous studies. The comparison of the luminosity functions between the different HSC-SSP fields suggests that a survey volume of >5 × 105 Mpc3 is essential to overcome cosmic variance. Since the current data have not reached the full depth expected for the HSC-SSP, the color cut in i - NB816 or z - NB921 induces a bias towards star-forming galaxies with large equivalent widths, primarily seen in the stellar mass functions for the H α emitters at z ≈ 0.25-0.40. Even so, the emission-line galaxies clearly cover a wide range of luminosity, stellar mass, and environment, thus demonstrating the usefulness of the narrowband data from the HSC-SSP for investigating star-forming galaxies at z < 1.5. [ABSTRACT FROM AUTHOR]

We present N/O abundance ratios, ionization parameters qion, and oxygen abundances O/H for a total of 41 galaxies (11 individual galaxies and a 30-galaxy stack) including Lya emitters and Lyman break galaxies at z ~ 2, and investigate galaxy evolution from z ~ 0 to 2 in conjunction with 208529 local galaxies from the Sloan Digital Sky Survey (SDSS) and nine green pea galaxies (GPs). In contrast with most of the recent studies, we obtain the N/O ratio, qion, and O/H measurements by direct Te methods using [OIII] λ4363 and OIII] λ1665 lines. Based on these reliable measurements, we find that there are z ~ 2 galaxies with excesses of N/O falling beyond the N/O-O/H relation of the local galaxies while the majority of the z ~ 2 galaxies have N/O ratios that are nearly comparable with those of z ~ 0 galaxies in the N/O-stellarmass relation. Our galaxies place the upper limit of the N/O ratio log(N/O) ≤ -1.26 on average, suggesting that the N/O ratio evolves, if at all, by <0.17 dex. Obtaining the reliable measurements free from the N/O-qion-O/H degeneracies, we demonstrate, for the first time, that z ~ 2 galaxies with offsets in the Baldwin-Phillips-Terlevich (BPT) diagram show (1) only an N/O excess, (2) only a qion excess, or (3) both N/O and qion excesses. We argue that the BPT offsets at z ~ 2 are not made by one of the (1)-(3) galaxy populations alone, but a composite of (1)-(3) populations. We confirm that these (1)-(3) populations also exist at z ~ 0, such as GPs and SDSS low-mass and high-SFR galaxies (LMHSs). [ABSTRACT FROM AUTHOR]

We have carried out panoramic Lyα narrow-band imaging with Suprime-Cam on Subaru towards the known protocluster USS1558-003 at z = 2.53. Our previous narrow-band imaging in the near-infrared identified multiple dense groups of Hα emitters (HAEs) within the protocluster. We have now identified the large-scale structures across a ~50 comoving Mpc scale traced by Lyα emitters (LAEs) in which the protocluster traced by the HAEs is embedded. On a smaller scale, however, there are remarkably few LAEs in the regions of HAE overdensities. Moreover, the stacking analyses of the images show that HAEs in higher-density regions show systematically lower escape fractions of Lyα photons than those of HAEs in lower-density regions. These phenomena may be driven by the extra depletion of Lyα emission lines along our line of sight by more intervening cold circumgalactic/intergalactic medium and/or dust in the dense core.We also caution that all the previous high-z protocluster surveys using LAEs as tracers would have largely missed galaxies in the very dense cores of the protoclusters where we would expect to see any early environmental effects. [ABSTRACT FROM AUTHOR]

We present physical properties of spectroscopically confirmed Lya emitters (LAEs) with very large rest-frame Lya equivalent widths EW0(Lya). Although the definition of large EW0(Lya) LAEs is usually difficult due to limited statistical and systematic uncertainties, we identify six LAEs selected from ~3000 LAEs at z ~ 2 with reliable measurements of EW0 (Lya) ⋍ 200-400 Å given by careful continuum determinations with our deep photometric and spectroscopic data. These large EW0(Lya) LAEs do not have signatures of AGN, but notably small stellar masses of M* = 107-8M⊙ and high specific star formation rates (star formation rate per unit galaxy stellar mass) of ~100 Gyr-1. These LAEs are characterized by the median values of L(Lya) = 3.7 × 1042 erg s-1 and MUV = -18.0 as well as the blue UV continuum slope of ß =-2.5 ± 0.2 and the low dust extinction E(B - V)* = 0.02+0.04-0.02, which indicate a high median Lya escape fraction of fLyaesc = 0.68 ± 0.30. This large fLyaesc value is explained by the low HI column density in the interstellar medium which is consistent with full width at half-maximum (FWHM) of the Lya line, FWHM(Lya) = 212 ± 32 km s-1, significantly narrower than those of small EW0(Lya) LAEs. Based on the stellar evolution models, our observational constraints of the large EW0 (Lya), the small ß, and the rest-frame He II EW imply that at least a half of our large EW0(Lya) LAEs would have young stellar ages of ⋍20 Myr and very low metallicities of Z < 0.02 Z⊙ regardless of the star formation history. [ABSTRACT FROM AUTHOR]

The physical properties and elemental abundances of the interstellar medium in galaxies during cosmic reionization are important for understanding the role of galaxies in this process. We report the Atacama Large Millimeter/submillimeter Array detection of an oxygen emission line at a wavelength of 88 micrometers from a galaxy at an epoch about 700 million years after the Big Bang. The oxygen abundance of this galaxy is estimated at about one-tenth that of the Sun. The nondetection of far-infrared continuum emission indicates a deficiency of interstellar dust in the galaxy. A carbon emission line at a wavelength of 158 micrometers is also not detected, implying an unusually small amount of neutral gas. These properties might allow ionizing photons to escape into the intergalactic medium. [ABSTRACT FROM AUTHOR]

We present statistical properties of diffuse Lyα haloes (LAHs) around high-z star-forming galaxies with large Subaru samples of Lyα emitters (LAEs) at z = 2.2. We make subsamples defined by the physical quantities of LAEs' central Lyα luminosities, ultraviolet (UV) magnitudes, Lyα equivalent widths, and UV slopes, and investigate LAHs' radial surface brightness (SB) profiles and scale lengths rn as a function of these physical quantities. We find that there exist prominent LAHs around LAEs with faint Lyα luminosities, bright UV luminosities, and small Lyα equivalent widths in cumulative radial Lyα SB profiles. We confirm this trend with the anticorrelation between rn and Lyα luminosities (equivalent widths) based on the Spearman's rank correlation coefficient that is ρ = -0.9 (-0.7) corresponding to the 96 per cent (93 per cent) confidence level, although the correlation between rn and UV magnitudes is not clearly found in the rank correlation coefficient. Our results suggest that LAEs with properties similar to typical Lyman-break galaxies (with faint Lyα luminosities and small equivalent widths) possess more prominent LAHs. We investigate scenarios for the major physical origins of LAHs with our results. Because we find relatively small Lyα equivalent widths up to 77 Å in LAHs that include LAEs' central components, these results suggest that the cold stream scenario is not preferred. There remain two possible scenarios of Lyα scattering in circumgalactic medium and satellite galaxies that cannot be tested with our observational data. [ABSTRACT FROM AUTHOR]

We report the discovery of a protocluster at z ~ 6 containing at least eight cluster member galaxies with spectroscopic confirmations in the wide-field image of the Subaru Deep Field (SDF). The overdensity of the protocluster is significant at the 6σ level, based on the surface number density of i'-dropout galaxies. The overdense region covers ~6' x 6' (14 Mpc x 14 Mpc in comoving units at z = 6) and includes 30 i'-dropout galaxies. Follow-up spectroscopy revealed that 15 of these are real z ~ 6 galaxies (5.7 < z < 6.3). Of these 15, 8 are clustering in a narrow redshift range (Δz < 0.05 centered at z = 6.01), corresponding to a seven-fold increase in number density over the average in redshift space. We found no significant difference in the observed properties, such as Lyα luminosities and UV continuum magnitudes, between the eight protocluster members and the seven non-members. The velocity dispersion of the eight protocluster members is 647 ± 124 km s-1 , which is about three times higher than that predicted by the standard cold darkmattermodel. This discrepancy could be attributed to the distinguishing three-dimensional distribution of the eight protocluster members. We discuss two possible explanations for this discrepancy: either the protocluster is already mature, with old galaxies at the center, or it is still immature and composed of three subgroups merging to become a larger cluster. In either case, this concentration of z = 6.01 galaxies in the SDF may be one of the first sites of formation of a galaxy cluster in the universe. [ABSTRACT FROM AUTHOR]

We report the Subaru Hyper Suprime-Cam (HSC) discovery of two Lyα blobs (LABs), dubbed z70-1 and z49-1 at z = 6.965 and z = 4.888, respectively, that are Lyα emitters with a bright () and spatially extended Lyα emission, and present the photometric and spectroscopic properties of a total of seven LABs: the two new LABs and five previously known LABs at z = 5.7–6.6. The z70-1 LAB shows extended Lyα emission with a scale length of 1.4 ± 0.2 kpc, about three times larger than the UV continuum emission, making z70-1 the most distant LAB identified to date. All of the seven LABs, except z49-1, exhibit no active galactic nucleus (AGN) signatures such as X-ray emission, N v λ1240 emission, or Lyα line broadening, while z49-1 has a strong C iv λ1548 emission line indicating an AGN on the basis of the UV-line ratio diagnostics. We carefully model the point-spread functions of the HSC images and conduct two-component exponential profile fitting to the extended Lyα emission of the LABs. The Lyα scale lengths of the core (star-forming region) and halo components are rc = 0.6–1.2 kpc and rh = 2.0–13.8 kpc, respectively. The relations between the scale lengths and galaxy properties (Lyα luminosity LLyα, Lyα rest-frame equivalent width EW0, and UV continuum magnitude MUV) of our LABs are similar to those of Lyα halos (LAHs) identified around star-forming galaxies found previously by the Very Large Telescope/MUSE at similar redshifts, suggesting that our LABs are likely the bright version of high-z LAHs. [ABSTRACT FROM AUTHOR]

We have obtained three-dimensional maps of the universe in ∼200 × 200 × 80 comoving Mpc3 (cMpc3) volumes each at z = 5.7 and 6.6 based on a spectroscopic sample of 179 galaxies that achieves ≳80% completeness down to the Lyα luminosity of , based on our Keck and Gemini observations and the literature. The maps reveal filamentary large-scale structures and two remarkable overdensities made out of at least 44 and 12 galaxies at z = 5.692 (z57OD) and z = 6.585 (z66OD), respectively, making z66OD the most distant overdensity spectroscopically confirmed to date, with >10 spectroscopically confirmed galaxies. We compare spatial distributions of submillimeter galaxies at z ≃ 4–6 with our z = 5.7 galaxies forming the large-scale structures, and detect a 99.97% signal of cross-correlation, indicative of a clear coincidence of dusty star-forming galaxy and dust-unobscured galaxy formation at this early epoch. The galaxies in z57OD and z66OD are actively forming stars with star-formation rates (SFRs) ≳5 times higher than the main sequence, and particularly the SFR density in z57OD is 10 times higher than the cosmic average at the redshift (a.k.a. the Madau-Lilly plot). Comparisons with numerical simulations suggest that z57OD and z66OD are protoclusters that are progenitors of the present-day clusters with halo masses of ∼1014M⊙. [ABSTRACT FROM AUTHOR]

We report 14 and 26 protocluster candidates at z = 5.7 and 6.6 over 14 and 16 deg2 areas, respectively, selected from 2230 (259) Lyα emitters (LAEs) photometrically (spectroscopically) identified using Subaru/Hyper Suprime-Cam (HSC) deep images (Keck, Subaru, and Magellan spectra, and literature data). Six out of the 40 protocluster candidates include one to 13 spectroscopically confirmed LAEs. We conduct Monte Carlo simulations to estimate how many protocluster candidates are found by chance for randomly distributed sources, and find that the effective number of protocluster candidates at z = 5.7 (6.6) is six (five). By comparing with the cosmological Lyα radiative transfer (RT) model reproducing the LAEs with reionization effects, we find that more than half of these protocluster candidates are progenitors of present-day clusters with mass of . We then investigate the correlation between the LAE overdensity δ and the Lyα rest-frame equivalent width , because the cosmological Lyα RT model suggests that the slope of the –δ relation steepens toward the epoch of cosmic reionization (EoR), due to the existence of ionized bubbles around galaxy overdensities easing the escape of Lyα emission from the partly neutral intergalactic medium. The available HSC data suggest that the slope of the –δ correlation does not evolve from the post-reionization epoch, z = 5.7, to the EoR, z = 6.6, beyond the moderately large statistical errors. There is a possibility that we could detect the evolution of the –δ relation from z = 5.7 to 7.3 using the upcoming HSC observations that will provide large samples of LAEs at z = 6.6–7.3. [ABSTRACT FROM AUTHOR]

We present the results of a survey of the brightest UV-selected galaxies in protoclusters. These proto-brightest cluster galaxy (proto-BCG) candidates are drawn from 179 overdense regions of g-dropout galaxies at z ∼ 4 from the Hyper Suprime-Cam Subaru Strategic Program identified previously as good protocluster candidates. This study is the first to extend the systematic study of the progenitors of BCGs from z ∼ 2 to z ∼ 4. We carefully remove possible contaminants from foreground galaxies and, for each structure, select the brightest galaxy that is at least 1 mag brighter than the fifth-brightest galaxy. We select 63 proto-BCG candidates and compare their properties with those of galaxies in the field and those of other galaxies in overdense structures. The proto-BCG candidates and their surrounding galaxies have different rest-UV color (i − z) distributions to field galaxies and other galaxies in protoclusters that do not host proto-BCGs. In addition, galaxies surrounding proto-BCGs are brighter than those in protoclusters without proto-BCGs. The image stacking analysis reveals that the average effective radius of proto-BCGs is ∼28% larger than that of field galaxies. The i − z color differences suggest that proto-BCGs and their surrounding galaxies are dustier than other galaxies at z ∼ 4. These results suggest that specific environmental effects or assembly biases have already emerged in some protoclusters as early as z ∼ 4, and we suggest that proto-BCGs have different star formation histories than other galaxies in the same epoch. [ABSTRACT FROM AUTHOR]

We present the Atacama Large Millimeter/submillimeter Array detection of the [O iii] 88 μm line and rest-frame 90 μm dust continuum emission in a Y-dropout Lyman break galaxy (LBG), MACS0416_Y1 lying behind the Frontier Field cluster MACS J0416.1−2403. This [O iii] detection confirms the LBG with a spectroscopic redshift of z = 8.3118 ± 0.0003, making this object one of the farthest galaxies ever identified spectroscopically. The observed 850 μm flux density of 137 ± 26 μJy corresponds to a de-lensed total infrared (IR) luminosity of if assuming a dust temperature of Tdust = 50 K and an emissivity index of β = 1.5, yielding a large dust mass of . The ultraviolet-to-far-IR spectral energy distribution modeling where the [O iii] emissivity model is incorporated suggests the presence of a young (τage ≈ 4 Myr), star-forming ( yr−1), moderately metal-polluted (Z ≈ 0.2Z⊙) stellar component with a mass of Mstar = 3 × 108M⊙. An analytic dust mass evolution model with a single episode of star formation does not reproduce the metallicity and dust mass in τage ≈ 4 Myr, suggesting a pre-existing evolved stellar component with Mstar ∼ 3 × 109M☉ and τage ∼ 0.3 Gyr as the origin of the dust mass. [ABSTRACT FROM AUTHOR]

We present the Lyα luminosity function (LF) derived from 34 Lyα emitters (LAEs) at z = 7.0 on an area of sky of 3.1 deg2, the largest sample of those in the literature to date obtained at a redshift z ≳ 7. The LAE sample is compiled from deep large-area narrowband observations with Subaru conducted by the Cosmic HydrOgen Reionization Unveiled with Subaru (CHORUS) project. The z = 7.0 Lyα LF of our project is consistent with those of the previous Dark Energy Camera and Subaru studies at the bright and faint ends, respectively, while having uncertainties that are significantly smaller than those of the previous study results. Exploiting the small errors of our measurements, we investigate the shape of the Lyα LF from the faint end to the bright end. We find that the shape of the z = 7.0 Lyα LF can be explained by the steep slope of α ≃ −2.5 suggested at z = 6.6, and that there is no clear signature of a bright-end excess at z ≃ 7 claimed by the previous work, which was thought to be created by the ionized bubbles around bright LAEs, whose Lyα photons could easily escape from the partly neutral intergalactic medium (IGM) at z ≃ 7. We estimate the Lyα luminosity densities (LDs) with Lyα LFs at z ≃ 6–8 given by our studies and the previous ones, and compare the evolution of the UV-continuum LD estimated with dropouts. The Lyα LD monotonically decreases from z ∼ 6 to 8, and evolves more strongly than the UV-continuum LD, which is indicative of the Lyα damping wing absorption of the IGM toward the heart of the reionization epoch. [ABSTRACT FROM AUTHOR]

We present morphological properties of dusty star-forming galaxies at z = 1–3 determined with the high-resolution (FWHM ∼ 0.″19) Atacama Large Milllimeter/submillimeter Array (ALMA) 1 mm map of our ASAGAO survey covering a 26 arcmin2 area in GOODS-S. In conjunction with the ALMA archival data, our sample consists of 45 ALMA sources with infrared luminosity (LIR) range of ∼1011–1013L⊙. To obtain an average rest-frame far-infrared (FIR) profile, we perform individual measurements and careful stacking of the ALMA sources using the uv-visibility method that includes positional-uncertainty and smoothing-effect evaluations through Monte Carlo simulations. We find that our sample has an average FIR-wavelength Sérsic index and effective radius of nFIR = 1.2 ± 0.2 and Re,FIR = 1.0–1.3 kpc, respectively, additionally with a point-source component at the center, indicative of the existence of active galactic nuclei. The average FIR profile agrees with a morphology of an exponential disk clearly distinguished from a de Vaucouleurs spheroidal profile (Sérsic index of 4). We also examine the rest-frame optical Sérsic index nopt and effective radius Re,opt with deep Hubble SpaceTelescope (HST) images. Interestingly, we obtain nopt = 0.9 ± 0.3 (≃nFIR) and Re,opt = 3.2 ± 0.6 kpc (>Re,FIR), suggesting that the dusty disk-like structure is embedded within a larger stellar disk. The rest-frame UV and FIR data of HST and ALMA provide us with a radial profile of the total star formation rate (SFR), where the infrared SFR dominates over the UV SFR at the center. Under the assumption of a constant SFR, a compact stellar distribution in z ∼ 1–2 compact quiescent galaxies (cQGs) is well reproduced, while a spheroidal stellar morphology of cQGs (nopt = 4) is not, suggestive of other important mechanism(s) such as dynamical dissipation. [ABSTRACT FROM AUTHOR]

Quasars (QSOs) hosting supermassive black holes are believed to reside in massive halos harboring galaxy overdensities. However, many observations revealed average or low galaxy densities around z ≳ 6 QSOs. This could be partly because they measured galaxy densities in only tens of arcmin2 around QSOs and might have overlooked potential larger-scale galaxy overdensities. Some previous studies also observed only Lyman break galaxies (LBGs; massive older galaxies) and missed low-mass young galaxies, like Lyα emitters (LAEs), around QSOs. Here we present observations of LAE and LBG candidates in ∼700 arcmin2 around a z = 6.61 luminous QSO using the Subaru Telescope Suprime-Cam with narrowband/broadband. We compare their sky distributions, number densities, and angular correlation functions with those of LAEs/LBGs detected in the same manner and comparable data quality in our control blank field. In the QSO field, LAEs and LBGs are clustering in 4–20 comoving Mpc angular scales, but LAEs show mostly underdensity over the field while LBGs are forming 30 × 60 comoving Mpc2 large-scale structure containing 3σ–7σ high-density clumps. The highest-density clump includes a bright (23.78 mag in the narrowband) extended (≳16 kpc) Lyα blob candidate, indicative of a dense environment. The QSO could be part of the structure but is not located exactly at any of the high-density peaks. Near the QSO, LAEs show underdensity while LBGs average to 4σ excess densities compared to the control field. If these environments reflect halo mass, the QSO may not be in the most massive halo but still in a moderately massive one. [ABSTRACT FROM AUTHOR]

We conduct a systematic study of galactic outflows in star-forming galaxies at based on the absorption lines of optical spectra taken from SDSS DR7, DEEP2 DR4, and Keck (Erb et al.). We carefully make stacked spectra of homogeneous galaxy samples with similar stellar mass distributions at and perform the multicomponent fitting of model absorption lines and stellar continua to the stacked spectra. We obtain the maximum () and central () outflow velocities and estimate the mass loading factors (η), a ratio of the mass outflow rate to the star formation rate (SFR). Investigating the redshift evolution of the outflow velocities measured with the absorption lines whose depths and ionization energies are similar (Na i D and Mg i at ; Mg ii and C ii at ), we identify, for the first time, that the average value of () significantly increases by 0.05–0.3 dex from to 2 at a given SFR. Moreover, we find that the value of η increases from to 2 by at a given halo circular velocity , albeit with a potential systematics caused by model parameter choices. The redshift evolution of () and η is consistent with the galaxy-size evolution and the local velocity–SFR surface density relation and explained by high gas fractions in high-redshift massive galaxies, which is supported by recent radio observations. We obtain a scaling relation of for in our galaxies that agrees with the momentum-driven outflow model () within the uncertainties. [ABSTRACT FROM AUTHOR]

We detect 20 z = 7.0 Lyα emitter (LAE) candidates to L(Lyα) ∼ 2 × 1042 erg s−1 or 0.3 and in a volume of 6.1 × 105 Mpc3 in the Subaru Deep Field and the Subaru/XMM-Newton Deep Survey field by 82 hr and 37 hr of Subaru Suprime-Cam narrowband NB973 and reddest optical y-band imaging. We compare their Lyα and UV luminosity functions (LFs) and densities and Lyα equivalent widths (EWs) to those of z = 5.7, 6.6, and 7.3 LAEs from previous Suprime-Cam surveys. The Lyα LF (density) rapidly declines by a factor of ×1.5 (1.9) in L(Lyα) at z = 5.7–6.6 (160 Myr), ×1.5 (1.6) at z = 6.6–7.0 (60 Myr) at the faint end, and ×2.0 (3.8) at z = 7.0–7.3 (40 Myr). Also, in addition to the systematic decrease in EW at z = 5.7–6.6 previously found, two-thirds of the z = 7.0 LAEs detected in the UV continuum exhibit lower EWs than the z = 6.6 ones. Moreover, while the UV LF and density do not evolve at z = 5.7–6.6, they modestly decline at z = 6.6–7.0, implying galaxy evolution contributing to the decline of the Lyα LF. Comparison of the z = 7.0 Lyα LF to the one predicted by an LAE evolution model further reveals that galaxy evolution alone cannot explain all of the decline of the Lyα LF. If we attribute the discrepancy to Lyα attenuation by neutral hydrogen, the intergalactic medium transmission of Lyα photons at z = 7.0 would be . It is lower (higher) than the at z = 6.6 (7.3) derived by previous studies, suggesting rapid increase in neutral fraction at z > 6. [ABSTRACT FROM AUTHOR]

We present clustering analysis results from 10,381 Lyman break galaxies (LBGs) at z ∼ 4–7, identified in the Hubble legacy deep imaging and new complimentary large-area Subaru/Hyper Suprime-Cam data. We measure the angular correlation functions of these LBGs at z ∼ 4, 5, 6, and 7 and fit these measurements using halo occupation distribution (HOD) models that provide an estimate of halo masses, . Our Mh estimates agree with those obtained by previous clustering studies in a UV-magnitude versus Mh plane and allow us to calculate stellar-to-halo mass ratios (SHMRs) of LBGs. By comparison with the SHMR, we identify evolution of the SHMR from to and from to at the >98% confidence levels. The SHMR decreases by a factor of ∼2 from to 4 and increases by a factor of ∼4 from to 7 at the dark matter halo mass of . We compare our SHMRs with results of a hydrodynamic simulation and a semianalytic model and find that these theoretical studies do not predict the SHMR increase from to 7. We obtain the baryon conversion efficiency (BCE) of LBGs at and find that the BCE increases with increasing dark matter halo mass. Finally, we compare our clustering+HOD estimates with results from abundance matching techniques and conclude that the Mh estimates of the clustering+HOD analyses agree with those of the simple abundance matching within a factor of 3, and that the agreement improves when using more sophisticated abundance matching techniques that include subhalos, incompleteness, and/or evolution in the star formation and stellar mass functions. [ABSTRACT FROM AUTHOR]

We present the results of an Lyα profile analysis of 12 Lyα emitters (LAEs) at with high-resolution Lyα spectra. We find that all 12 objects have an Lyα profile with the main peak redward of the systemic redshift defined by nebular lines, and five have a weak, secondary peak blueward of the systemic redshift (blue bump). The average velocity offset of the red main peak (the blue bump, if any) with respect to the systemic redshift is km s−1 ( km s−1), which is smaller than (comparable to) that of Lyman break galaxies (LBGs). The outflow velocities inferred from metal absorption lines in three individual and one stacked spectra are comparable to those of LBGs. The uniform expanding shell model constructed by Verhamme et al. reproduces not only the Lyα profiles but also other observed quantities, including the outflow velocity and the FWHM of nebular lines for the non-blue-bump objects. On the other hand, the model predicts too high FWHMs of nebular lines for the blue bump objects, although this discrepancy may disappear if we introduce additional Lyα photons produced by gravitational cooling. We show that the small values of our sample can be explained by low neutral hydrogen column densities of log() = 18.9 cm−2 on average. This value is more than one order of magnitude lower than those of LBGs but is consistent with recent findings that LAEs have high ionization parameters and low H i gas masses. This result suggests that low values, giving reduced numbers of resonant scattering of Lyα photons, are the key to the strong Lyα emission of LAEs. [ABSTRACT FROM AUTHOR]