Search

We present statistics of z ∼ 6–9 galaxy outflows indicated by spatially extended gas emission and broad lines. With a total of 61 spectroscopically confirmed galaxies at z ∼ 6–9 in the JWST CEERS, GLASS, and ERO data, we find four galaxies with [O iii ] + H β ionized gas emission significantly extended beyond the kiloparsec-scale stellar components on the basis of the emission line images constructed by the subtraction of NIRCam broadband (line on/off-band) images. By comparison with low- z galaxies, the fraction of galaxies with spatially extended gas, 4/18, at z ∼ 6–9 is an order of magnitude higher than that at z ∼ 0–1, which can be explained by events triggered by frequent major mergers at high redshift. We also investigate medium- and high-resolution NIRSpec spectra of 30 galaxies at z ∼ 6–9, and identify five galaxies with broad (140−800 km s−1) lines in the [O iii ] forbidden line emission, suggestive of galaxy outflows. One galaxy at z = 6.38 shows both spatially extended gas emission and the broad lines, while none of the galaxies with spatially extended gas emission or broad lines present a clear signature of active galactic nuclei (AGN) in either the line diagnostics or type 1 AGN line broadening (>1000 km s−1), which suggests that outflows are mainly driven by stellar feedback. The existence of galaxies with/without spatially extended gas emission or broad lines may be explained by different viewing angles toward outflows or the fact that these are galaxies in the early, late, or post phases of galaxy outflows at high redshift, where relatively large fractions of such galaxies indicate longer-duration and/or more frequent outflows at early cosmic epochs. [ABSTRACT FROM AUTHOR]

We present ionizing spectra estimated at 13.6–100 eV for 10 dwarf galaxies with strong high-ionization lines of He ii λ 4686 and [Ne v ] λ 3426 ([Ne iv ] λ 2424) at z = 0 (z = 8) that are identified in our Keck/LRIS spectroscopy and the literature (the JWST Early Release Observations program). With the flux ratios of these high-ionization lines and >10 low-ionization lines of hydrogen, helium, oxygen, neon, and sulfur, we determine ionizing spectra consisting of stellar and nonthermal power-law radiation by photoionization modeling with free parameters of nebular properties, including metallicity and ionization parameter, canceling out abundance ratio differences. We find that all of the observed flux ratios are well reproduced by the photoionization models with the power-law index α EUV of α EUV ∼ (–1) − 0 and the luminosity L EUV of L EUV ∼ 1040–1042 erg s−1 at ∼55–100 eV for six galaxies, while four galaxies include large systematics in α EUV caused by stellar radiation contamination. We then compare α EUV and L EUV of these six galaxies with those predicted by the black hole (BH) accretion disk models and find that α EUV and L EUV are similar to those of the intermediate-mass BHs (IMBHs) in BH accretion disk models, albeit with possibilities of the other scenarios. Confirming these results with a known IMBH having a mass M BH of M BH = 105.75 M ⊙, we find that four local galaxies and one z = 7.665 galaxy have ionizing spectra consistent with those of IMBHs with M BH ∼ 103–105 M ⊙. [ABSTRACT FROM AUTHOR]

We present the rest-frame optical and UV surface brightness (SB) profiles for 149 galaxies with M opt < −19.4 mag at z = 4–10 (29 of which are spectroscopically confirmed with JWST NIRSpec), securing high signal-to-noise ratios of 10–135 with deep JWST NIRCam 1– |$5\, \mu$| m images obtained by the CEERS survey. We derive morphologies of our high- z galaxies, carefully evaluating the systematics of SB profile measurements with Monte Carlo simulations as well as the impacts of a) AGNs, b) multiple clumps including galaxy mergers, c) spatial resolution differences with previous HST studies, and d) strong emission lines, e.g. Hα and [O  iii ], on optical morphologies with medium-band F410M images. Conducting Sérsic profile fitting for our high- z galaxy SBs with GALFIT, we obtain effective radius ranges for optical r e,opt and UV r e,UV wavelengths of r e, opt = 0.05–1.6 kpc and r e,UV = 0.03–1.7 kpc that are consistent with previous results within large scatters in the size–luminosity relations. However, we find that the effective radius ratio, r e,opt |$/$| r e,UV, is almost unity, |$1.01^{+0.35}_{-0.22}$|⁠ , over z = 4–10 with no signatures of past inside-out star formation such as found at z ∼ 0–2. There are no spatial offsets exceeding 3σ between the optical and UV morphology centers in cases of no mergers, indicative of major star-forming activity only being found near mass centers of galaxies at z ≳ 4 probably experiencing the first phase of inside-out galaxy formation. [ABSTRACT FROM AUTHOR]

We present a protocluster search covering z ∼ 3 to z ∼ 5 based on the combination of the Hyper SuprimeCam Subaru Strategic Programme and the CFHT Large Area U -band Deep Survey. We identify about 30 protocluster candidates per unit redshift over the |$\sim 25\, \mathrm{deg^2}$| area of the Deep/UltraDeep layer. Protocluster candidates are selected as regions with a significantly enhanced surface density of dropout galaxies. With this large sample, we characterize the properties of their individual member galaxies. We compare the number counts of dropout galaxies in protocluster candidates with that of coeval field galaxies. Rest-frame ultraviolet (UV) bright galaxies are overabundant in protocluster candidates, a trend seen across the full redshift range studied. We do not find evidence for their spatial distribution within protocluster candidates to be distinct from their fainter counterparts, nor for their UV colour to be different from that of field galaxies with the same brightness. Cosmological simulations predict this bright-end excess, with the main cause being a richer population of massive galaxies, with only a minor contribution from an enhancement in star formation activity (and therefore UV emission) at fixed mass. U -to- K SED modelling of our observed samples supports this interpretation. This environmental differentiation in number counts is already in place at z ∼ 5, with no significant redshift dependence over the range in lookback times probed. These observational results and model predictions suggest that the cosmic clock is ahead in high-density environments. [ABSTRACT FROM AUTHOR]

We study the formation of the first galaxies in overdense regions modelled by the FORmation and EVolution of galaxies in Extremely overdense Regions motivated by SSA22 (FOREVER22) simulation project. Our simulations successfully reproduce the star formation rates and the M UV– M star relations of candidate galaxies at z ∼ 10–14 observed by the JWST. We suggest that the observed galaxies are hosted by dark matter haloes with M h ≳ 1010 M⊙ and are in short-period starburst phases. On the other hand, even simulated massive galaxies in overdense regions cannot reproduce the intense star formation rates and the large stellar masses of observed candidates at z ∼ 16. Also, we show that the contribution of Population III stars to the ultraviolet (UV) flux decreases as the stellar mass increases and it is a few per cent for galaxies with M star ∼ 107 M⊙. Therefore, a part of the observed flux by JWST could be the light from Population III stars. Our simulations suggest that the UV flux can be dominated by Population III stars and the UV slope shows β ≲ −3 if future observations would reach galaxies with M stars ∼ 105 M⊙ at z  ∼ 20 of which the mass fraction of Population III stars can be greater than 10 per cent. [ABSTRACT FROM AUTHOR]

We report Atacama Large Millimeter/submillimeter Array Band 3 observations of CO(6−5), CO(7−6), and [C i ](2−1) in B14-65666 ("Big Three Dragons"), one of the brightest Lyman-break galaxies at z > 7 in the rest-frame ultraviolet continuum, far-infrared continuum, and emission lines of [O iii ] 88 μ m and [C ii ] 158 μ m. CO(6−5), CO(7−6), and [C i ](2−1), whose 3 σ upper limits on the luminosities are approximately 40 times fainter than the [C ii ] luminosity, are all not detected. The L [C II ]/ L CO(6–5) and L [C II ]/ L CO(7–6) ratios are higher than the typical ratios obtained in dusty star-forming galaxies or quasar host galaxies at similar redshifts, and they may suggest a lower gas density in the photodissociated region in B14-65666. By using the (1) [C ii ] luminosity, (2) dust mass-to-gas mass ratio, and (3) a dynamical mass estimate, we find that the molecular gas mass (M mol) is (0.05–11) × 1010 M ⊙. This value is consistent with the upper limit inferred from the nondetection of mid- J CO and [C i ](2−1). Despite the large uncertainty in M mol, we estimate a molecular gas-to-stellar mass ratio (μ gas) of 0.65–140 and a gas depletion time (τ dep) of 2.5–550 Myr; these values are broadly consistent with those of other high-redshift galaxies. B14-65666 could be an ancestor of a passive galaxy at z ≳ 4 if no gas is fueled from outside the galaxy. [ABSTRACT FROM AUTHOR]

We search for local extremely metal-poor galaxies (EMPGs), selecting photometric candidates by broadband color excess and machine-learning techniques with the SDSS photometric data. After removing stellar contaminants by shallow spectroscopy with Seimei and Nayuta telescopes, we confirm that three candidates are EMPGs with 0.05–0.1 Z ⊙ by deep Magellan/MagE spectroscopy for faint [Oiii] λ 4363 lines. Using a statistical sample consisting of 105 spectroscopically confirmed EMPGs taken from our study and the literature, we calculate the cross-correlation function (CCF) of the EMPGs and all SDSS galaxies to quantify environments of EMPGs. Comparing another CCF of all SDSS galaxies and comparison of SDSS galaxies in the same stellar-mass range (107.0–108.4 M ⊙), we find no significant (>1 σ) difference between these two CCFs. We also compare mass–metallicity relations (MZRs) of the EMPGs and those of galaxies at z ∼ 0–4 with a steady chemical evolution model and find that the EMPG MZR is comparable with the model prediction on average. These clustering and chemical properties of EMPGs are explained by a scenario of stochastic metal-poor gas accretion on metal-rich galaxies showing metal-poor star formation. Extending the broadband color excess technique to a high- z EMPG search, we select 17 candidates of z ∼ 4–5 EMPGs with the deep (≃30 mag) near-infrared JWST/NIRCam images obtained by ERO and ERS programs. We find galaxy candidates with negligible [Oiii] λ λ 4959,5007 emission weaker than the local EMPGs and known high- z galaxies, suggesting that some of these candidates may fall in the range of 0–0.01 Z ⊙, which potentially breaks the lowest metallicity limit known to date. [ABSTRACT FROM AUTHOR]

We present cosmological-scale three-dimensional neutral hydrogen (H i) tomographic maps at z = 2–3 over a total of 837 deg2 in two blank fields that are developed with Ly α forest absorptions of 14,736 background Sloan Digital Sky Survey (SDSS) quasars at z = 2.08–3.67. Using the tomographic maps, we investigate the large-scale (≳10 h −1 cMpc) average H i radial profiles and two-direction profiles of the line-of-sight (LOS) and transverse directions around galaxies and active galactic nuclei (AGNs) at z = 2–3 identified by the Hobby–Eberly Telescope Dark Energy eXperiment survey and SDSS, respectively. The peak of the H i radial profile around galaxies is lower than the one around AGNs, suggesting that the dark matter halos of galaxies are less massive on average than those of AGNs. The LOS profile of AGNs is narrower than the transverse profile, indicating the Kaiser effect. There exist weak absorption outskirts at ≳30 h −1 cMpc beyond H i structures of galaxies and AGNs found in the LOS profiles that can be explained by the H i gas at ≳30 h −1 cMpc falling toward the source position. Our findings indicate that the H i radial profile of AGNs has transitions from proximity zones (≲a few h −1 cMpc) to the H i structures (∼1–30 h −1 cMpc) and the weak absorption outskirts (≳30 h −1 cMpc). Although there is no significant dependence of AGN types (type 1 vs. type 2) on the H i profiles, the peaks of the radial profiles anticorrelate with AGN luminosities, suggesting that AGNs' ionization effects are stronger than the gas mass differences. [ABSTRACT FROM AUTHOR]

We report on the galaxy density environment around a high- z radio galaxy (HzRG) at z = 4.72, HSC J083913.17+011308.1 (HSC J0839+0113), probed using an r -dropout Lyman break galaxy (LBG) sample from the Hyper Suprime-Cam Subaru Strategic Program data. We find that HSC J0839+0113 resides in the outskirts of an overdense region identified by the r -dropout galaxies at a 4.7σ significance level. The projected distance between HSC J0839+0113 and the peak position of the overdense region is 0.4 physical Mpc, which is shorter than the typical protocluster radius in this epoch. According to the extended Press–Schechter and the light cone models, the HSC J0839+0113-hosted overdense region is expected to evolve into a halo >1014  |${M_{\odot}}$| at z = 0 with a high probability of |$>\!\! 80\%$|⁠. These findings suggest that HSC J0839+0113 is associated with a protocluster. The HSC J0839+0113 rich-system is the most overdense region of LBGs among the known protoclusters with LBGs in the same cosmic epoch. [ABSTRACT FROM AUTHOR]

Strong high-ionization lines such as He ii of young galaxies are puzzling at high and low redshift. Although recent studies suggest the existence of nonthermal sources, whether their ionizing spectra can consistently explain multiple major emission lines remains a question. Here we derive the general shapes of the ionizing spectra for three local extremely metal-poor galaxies (EMPGs) that show strong He ii λ 4686. We parameterize the ionizing spectra composed of a blackbody and power-law radiation mimicking various stellar and nonthermal sources. We use photoionization models for nebulae and determine seven parameters of the ionizing spectra and nebulae by Markov Chain Monte Carlo methods, carefully avoiding systematics of abundance ratios. We obtain the general shapes of ionizing spectra explaining ∼10 major emission lines within observational errors with smooth connections from observed X-ray and optical continua. We find that an ionizing spectrum of one EMPG has a blackbody-dominated shape, while the others have convex downward shapes at >13.6 eV, which indicate a diversity of the ionizing spectrum shapes. We confirm that the convex downward shapes are fundamentally different from ordinary stellar spectrum shapes, and that the spectrum shapes of these galaxies are generally explained by the combination of the stellar and ultraluminous X-ray sources. Comparisons with stellar synthesis models suggest that the diversity of the spectrum shapes arises from differences in the stellar age. If galaxies at z ≳ 6 are similar to the EMPGs, high-energy (>54.4 eV) photons of the nonstellar sources negligibly contribute to cosmic reionization due to relatively weak radiation. [ABSTRACT FROM AUTHOR]

We present Keck/LRIS follow-up spectroscopy for 13 photometric candidates of extremely metal-poor galaxies (EMPGs) selected by a machine-learning technique applied to the deep (∼26 AB mag) optical and wide-area (∼500 deg2) Subaru imaging data in the EMPRESS survey. Nine out of the 13 candidates are EMPGs with an oxygen abundance (O/H) less than ∼10% solar value (O/H)⊙, and four sources are contaminants of moderately metal-rich galaxies or no emission-line objects. Notably, two out of the nine EMPGs have extremely low stellar masses and oxygen abundances of 5 Ă— 104â€"7 Ă— 105 M ⊙ and 2%â€"3% (O/H)⊙, respectively. With a sample of five EMPGs with (Fe/O) measurements, two (three) of which are taken from this study (the literature), we confirm that two EMPGs with the lowest (O/H) ratios of ∼2% (O/H)⊙ show high (Fe/O) ratios of ∼0.1, close to the solar abundance ratio. Comparing galaxy chemical enrichment models, we find that the two EMPGs cannot be explained by a scenario of metal-poor gas accretion/episodic star formation history due to their low (N/O) ratios. We conclude that the two EMPGs can be reproduced by the inclusion of bright hypernovae and/or hypothetical pair-instability supernovae (SNe) preferentially produced in a metal-poor environment. This conclusion implies that primordial galaxies at z ∼ 10 could have a high abundance of Fe that did not originate from Type Ia SNe with delays and that Fe may not serve as a cosmic clock for primordial galaxies. [ABSTRACT FROM AUTHOR]

We present the first measurement of the metallicity gradient in extremely metal-poor galaxies (EMPGs). With Subaru/Faint Object Camera And Spectrograph (FOCAS) Integral Field Unit (IFU), we have observed a nearby, low-mass EMPG, HSC J1631+4426, whose oxygen abundance and stellar mass are known to be 12 + log (O/H) = 6.9 and log10(M */ M ⊙) = 5.8, respectively. The measured metallicity gradient is −0.36 ± 0.04 dex kpc−1 corresponding to −0.049 ± 0.006 dex |$\:R_\mathrm{e}^{-1}$| for the continuum effective radius of R e = 0.14 kpc. Our observation has successfully demonstrated that three-dimensional spectroscopy with 8 m-class telescopes is powerful enough to reveal the metallicity distribution in local EMPGs, providing precious information on the baryon cycle in local analogs of primordial galaxies in the early Universe. [ABSTRACT FROM AUTHOR]

We present the morphology and stellar population of 27 extremely metal-poor galaxies (EMPGs) at z ∼ 0 with metallicities of 0.01–0.1 Z⊙. We conduct multicomponent surface brightness (SB) profile fitting for the deep Subaru/Hyper Suprime-Cam i-band images of the EMPGs with the Galfit software, carefully removing the SB contributions of tails. We find that the EMPGs with a median stellar mass of have a median Sérsic index of n = 1.1 and a median effective radius of re = 200 pc, suggesting that typical EMPGs have a very compact disk. We compare the EMPGs with z ∼ 6 galaxies and local galaxies on the size–mass (re–M*) diagram, and identify that the majority of the EMPGs have an re–M* relation similar to z ∼ 0 star-forming galaxies rather than z ∼ 6 galaxies. Not every EMPG is a local analog of high-z young galaxies in the re–M* relation. A spectrum of one pair of EMPG and tail, so far available, indicates that the tail is dynamically related to the EMPG with a median velocity difference of ΔV = 101 ± 32 km s−1. This moderately large ΔV cannot be explained by the dynamics of the tail, but likely by the infall on the tail. For the first time, we may identify the metal-poor star-forming system just now infalling into the tail. [ABSTRACT FROM AUTHOR]

We present results of the cross-correlation Lyα intensity mapping with Subaru/Hyper Suprime-Cam (HSC) ultra-deep narrowband images and Lyα emitters (LAEs) at z = 5.7 and 6.6 in a total area of 4 deg2. Although an overwhelming amount of data quality controls have been performed for the narrowband images, we further conduct extensive analyses evaluating systematics of large-scale point-spread function wings, sky subtractions, and unknown errors based on physically uncorrelated signals and sources found in real HSC images and object catalogs, respectively. Removing the systematics, we carefully calculate cross-correlations between Lyα intensity of the narrowband images and the LAEs. We tentatively identify very diffuse Lyα emission with the ≃3σ (≃2σ) significance at ≳100 comoving kiloparsecs (ckpc) far from the LAEs at z = 5.7 (6.6), around and probably even beyond a virial radius of star-forming galaxies with Mh ∼ 1011M⊙. The diffuse Lyα emission possibly extends up to 1000 ckpc with the surface brightness of 10−20–10−19 erg s−1 cm−2 arcsec−2. We confirm that the small-scale (<150 ckpc) Lyα radial profiles of LAEs are consistent with those obtained by recent Multi-Unit Spectroscopic Explorer observations. Comparisons with numerical simulations suggest that the large-scale (∼150–1000 ckpc) Lyα emission are not explained by unresolved faint neighboring galaxies including satellites, but by a combination of Lyα photons emitted from the central LAE and other unknown sources, such as cold-gas streams and galactic outflow. We find no evolution in the Lyα radial profiles of our LAEs from z = 5.7 to 6.6, where theoretical models predict a flattening of the profile slope made by cosmic reionization, albeit with our moderately large observational errors. [ABSTRACT FROM AUTHOR]

We present element abundance ratios and ionizing radiation of local young low-mass (∼106 M⊙) extremely metal-poor galaxies (EMPGs) with a 2% solar oxygen abundance (O/H)⊙ and a high specific star formation rate (sSFR ∼ 300 Gyr−1) and other (extremely) metal-poor galaxies, which are compiled from Extremely Metal-Poor Representatives Explored by the Subaru Survey (EMPRESS) and the literature. Weak emission lines such as [Fe iii ] λ4658 and He ii λ4686 are detected in very deep optical spectra of the EMPGs taken with 8 m class telescopes, including Keck and Subaru, enabling us to derive element abundance ratios with photoionization models. We find that neon-to-oxygen and argon-to-oxygen ratios are comparable to those of known local dwarf galaxies and that the nitrogen-to-oxygen abundance ratios (N/O) are lower than 20% (N/O)⊙, consistent with the low oxygen abundance. However, the iron-to-oxygen abundance ratios (Fe/O) of the EMPGs are generally high; the EMPGs with the 2%-solar oxygen abundance show high Fe/O ratios of ∼90%–140% (Fe/O)⊙, which are unlikely to be explained by suggested scenarios of Type Ia supernova iron productions, iron's dust depletion, and metal-poor gas inflow onto previously metal-riched galaxies with solar abundances. Moreover, the EMPGs with the 2%-solar oxygen abundance have very high He ii λ4686/Hβ ratios of ∼1/40, which are not reproduced by existing models of high-mass X-ray binaries with progenitor stellar masses <120 M⊙. Comparing stellar-nucleosynthesis and photoionization models with a comprehensive sample of EMPGs identified by this and previous EMPG studies, we propose that both the high Fe/O ratios and the high He ii λ4686/Hβ ratios are explained by the past existence of supermassive (>300 M⊙) stars, which may evolve into intermediate-mass black holes (≳100 M⊙). [ABSTRACT FROM AUTHOR]

We present bright [C ii ] 158 μm line detections from a strongly magnified and multiply imaged (μ ∼ 20–160) sub–L* () Lyman-break galaxy (LBG) at z = 6.0719 ± 0.0004, drawn from the ALMA Lensing Cluster Survey (ALCS). Emission lines are identified at 268.7 GHz at ≥8σ exactly at the positions of two multiple images of the LBG, behind the massive galaxy cluster RXCJ0600−2007. Our lens models, updated with the latest spectroscopy from VLT/MUSE, indicate that a sub region of the LBG crosses the caustic, and is lensed into a long (∼6″) arc with a local magnification of μ ∼ 160, for which the [C ii ] line is also significantly detected. The source plane reconstruction resolves the interstellar medium (ISM) structure, showing that the [C ii ] line is co-spatial with the rest-frame UV continuum at a scale of ∼300 pc. The [C ii ] line properties suggest that the LBG is a rotation-dominated system, whose velocity gradient explains a slight difference in redshifts between the whole LBG and its sub-region. The star formation rate (SFR)–L[CII] relations, for whole and sub-regions of the LBG, are consistent with those of local galaxies. We evaluate the lower limit of the faint-end of the [C ii ] luminosity function at z = 6, finding it to be consistent with predictions from semi-analytical models and from the local SFR–L[CII] relation with a SFR function at z = 6. These results imply that the local SFR–L[CII] relation is universal for a wide range of scales, including the spatially resolved ISM, the whole region of the galaxy, and the cosmic scale, even in the epoch of reionization. [ABSTRACT FROM AUTHOR]

We have initiated a new survey for local extremely metal-poor galaxies (EMPGs) with Subaru/Hyper Suprime-Cam (HSC) large-area (∼500 deg2) optical images reaching a 5σ limit of ∼26 mag, about 100 times deeper than the Sloan Digital Sky Survey (SDSS). To select Z/Z⊙ < 0.1 EMPGs from ∼40 million sources detected in the Subaru images, we first develop a machine-learning (ML) classifier based on a deep neural network algorithm with a training data set consisting of optical photometry of galaxy, star, and QSO models. We test our ML classifier with SDSS objects having spectroscopic metallicity measurements and confirm that our ML classifier accomplishes 86% completeness and 46% purity EMPG classifications with photometric data. Applying our ML classifier to the photometric data of the Subaru sources, as well as faint SDSS objects with no spectroscopic data, we obtain 27 and 86 EMPG candidates from the Subaru and SDSS photometric data, respectively. We conduct optical follow-up spectroscopy for 10 of our EMPG candidates with Magellan/LDSS-3+MagE, Keck/DEIMOS, and Subaru/FOCAS and find that the 10 EMPG candidates are star-forming galaxies at z = 0.007–0.03 with large Hβ equivalent widths of 104–265 Å, stellar masses of log(/) = 5.0–7.1, and high specific star formation rates of ∼300 Gyr−1, which are similar to those of early galaxies at z ≳ 6 reported recently. We spectroscopically confirm that 3 out of 10 candidates are truly EMPGs with Z/Z⊙ < 0.1, one of which is HSC J1631+4426, the most metal-poor galaxy, with Z/Z⊙ = 0.016, ever reported. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We present an IGM H i tomographic map in a survey volume of (cMpc3) centered at MAMMOTH-1 nebula and three neighboring quasars at z = 2.3. The MAMMOTH-1 nebula is an enormous Lyα nebula (ELAN), hosted by a type-II quasar dubbed MAMMOTH1-QSO, that extends over cMpc with no clear physical origin. Here we investigate the H i -gas distribution around MAMMOTH1-QSO with the ELAN and three neighboring type-I quasars, making the IGM H i tomographic map with a spatial resolution of 2.6 h−1 cMpc. Our H i tomographic map is reconstructed with H i Lyα forest absorption of bright background objects at z = 2.4–2.9: one eBOSS quasar and 16 Keck/LRIS galaxy spectra. We estimate the radial profile of H i overdensity for MAMMOTH1-QSO, and find that MAMMOTH1-QSO resides in a volume with fairly weak H i absorption. This suggests that MAMMOTH1-QSO may have a proximity zone where quasar illuminates and photoionizes the surrounding H i gas and suppresses H i absorption, and that the ELAN is probably a photoionized cloud embedded in the cosmic web. The H i radial profile of MAMMOTH1-QSO is very similar to those of three neighboring type-I quasars at z = 2.3, which is compatible with the AGN unification model. We compare the distributions of the H i absorption and star-forming galaxies in our survey volume, and identify a spatial offset between density peaks of star-forming galaxies and H i gas. This segregation may suggest anisotropic UV background radiation created by star-forming galaxy density fluctuations. [ABSTRACT FROM AUTHOR]

We present the first systematic search for extended metal-line [O II] λλ3726, 3729 nebulae, or [O II] blobs (O IIBs), at z = 1.2 using deep narrowband imaging with a survey volume of 1.9 × 105 Mpc3 on the 0.62 deg2 sky of Subaru-XMM Deep Survey (SXDS) field. We discover a giant O IIB, called “O IIB 1,” with a spatial extent over ∼75 kpc at a spectroscopic redshift of z = 1.18, and also identify a total of 12 O IIBs with a size of >30 kpc. Our optical spectrum of O IIB 1 presents [Ne V] λ3426 line at the 6σ level, indicating that this object harbors an obscured type-2 active galactic nucleus (AGN). The presence of gas outflows in this object is suggested by two marginal detections of Fe II λ2587 absorption and Fe II* λ2613 emission lines both of which are blueshifted at as large as 500-600 km s–1, indicating that the heating source of O IIB 1 is AGN or associated shock excitation rather than supernovae produced by starbursts. The number density of O IIB 1-type giant blobs is estimated to be ∼5 × 10–6 Mpc–3 at z ∼ 1.2, which is comparable with that of AGNs driving outflow at a similar redshift, suggesting that giant O IIBs are produced only by AGN activity. On the other hand, the number density of small O IIBs, 6 × 10–5 Mpc–3, compared to that of z ∼ 1 galaxies in the blue cloud in the same MB range, may imply that 3% of star-forming galaxies at z ∼ 1 are quenching star formation through outflows involving extended [O II] emission. [ABSTRACT FROM AUTHOR]

We report deep ALMA observations complemented by associated Hubble Space Telescope (HST) imaging for a luminous (mUV = 25) galaxy, “Himiko,” at a redshift of z = 6.595. The galaxy is remarkable for its high star formation rate, 100 M☼ yr–1, which has been securely estimated from our deep HST and Spitzer photometry, and the absence of any evidence for strong active galactic nucleus activity or gravitational lensing magnification. Our ALMA observations probe an order of magnitude deeper than previous IRAM observations, yet fail to detect a 1.2 mm dust continuum, indicating a flux of <52 μJy, which is comparable to or weaker than that of local dwarf irregulars with much lower star formation rates. We likewise provide a strong upper limit for the flux of [C II] 158 μm, , which is a diagnostic of the hot interstellar gas that is often described as a valuable probe for early galaxies. In fact, our observations indicate that Himiko lies off the local -star formation rate scaling relation by a factor of more than 30. Both aspects of our ALMA observations suggest that Himiko is a unique object with a very low dust content and perhaps nearly primordial interstellar gas. Our HST images provide unique insight into the morphology of this remarkable source, highlighting an extremely blue core of activity and two less extreme associated clumps. Himiko is undergoing a triple major merger event whose extensive ionized nebula of Lyα emitting gas, discovered in our earlier work with Subaru, is powered by star formation and the dense circumgalactic gas. We are likely witnessing an early massive galaxy during a key period of its mass assembly close to the end of the reionization era. [ABSTRACT FROM AUTHOR]

We present the average metallicity and star formation rate (SFR) of Lyα emitters (LAEs) measured from our large-area survey with three narrowband (NB) filters covering the Lyα, [O II]λ3727, and Hα+[N II] lines of LAEs at ɀ = 2.2. We select 919 ɀ = 2.2 LAEs from Subaru/Suprime-Cam NB data in conjunction with Magellan/IMACS spectroscopy. Of these LAEs, 561 and 105 are observed with KPNO/NEWFIRM near-infrared NB filters whose central wavelengths are matched to redshifted [O II] and Hot nebular lines, respectively. By stacking the neat-infrared images of the LAEs, we successfully obtain average nebular-line fluxes of LAEs, the majority of which are too faint to be identified individually by NB imaging or deep spectroscopy. The stacked object has an Hα luminosity of 1.7 x 1042 erg s-1 corresponding to an SFR of 14 Mʘ yr-1. We place, for the first time, a firm lower limit to the average metallicity of LAEs of Z Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. 0.09 Zʘ (2#x03C3; ) based on the [O II]/(Hα1;+[N II) index together with photoionization models and empirical relations. This lower limit of metallicity rules out the hypothesis that LAEs, so far observed at ɀ ~ 2, are extremely metal-poor (Z < 2 x 10-2 Zʘ) galaxies at the 4σ level. This limit is higher taan a simple extrapolation of the observed mass-metallicity relation of ɀ ~ 2 UV-selected galaxies toward lower masses (5 x 108 Mʘ), but roughly consistent with a recently proposed fundamental mass-metallicity relation when the LAEs' relatively low SFR is taken into account. The Hα and Lyα luminosities of our NB-selected LAEs indicate that the escape fraction of Lyα photons is ~12%-30%, much higher than the values derived for other galaxy populations at ɀ ~ 2. [ABSTRACT FROM AUTHOR]

We present the results of our ultra-deep Keck/DEIMOS spectroscopy of z-dropout galaxies in the Subaru Deep Field and Great Observatories Origins Deep Survey's northern field. For 3 out of 11 objects, we detect an emission line at ~ 1 µm with a signal-to-noise ratio of ~ 10. The lines show asymmetric profiles with high weighted skewness values, consistent with being Lyα, yielding redshifts of z = 7.213, 6.965, and 6.844. Specifically, we confirm the z = 7.213 objects in two independent DEIMOS runs with different spectroscopic configurations. The z = 6.965 object is a known Lyα emitter, IOK-1, for which our improved spectrum at a higher resolution yields a robust skewness measurement. The three z-dropouts have Lyα fluxes of 3 x 10-17 erg s-1 cm-2 and rest-frame equivalent widths Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. = 33-43 Å. Based on the largest spectroscopic sample of 43 z-dropouts, which is the combination of our and previous data, we find that the fraction of Lyα-emitting galaxies (Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. > 25 Å) is low at z ~ 7; 17% ± 10% and 24% ± 12% for bright (MUV ≃ -21) and faint (MUV ≃ -19.5) galaxies, respectively. The fractions of Lyα-emitting galaxies drop from z ~ 6 to 7 and the amplitude of the drop is larger for faint galaxies than for bright galaxies. These two pieces of evidence would indicate that the neutral hydrogen fraction of the intergalactic medium increases from z ~ 6 to 7 and that the reionization proceeds from high- to low-density environments, as suggested by an inside-out reionization model. [ABSTRACT FROM AUTHOR]

We investigate the stellar populations of Lyα emitters (LAEs) at and 3.7 in 0.65 deg2 of the Subaru/ XMM–Newton Deep Field, based on rest-frame ultraviolet-to-optical photometry obtained from the Subaru/ XMM–Newton Deep Survey, the UKIRT Infrared Deep Sky Survey/Ultra Deep Survey (UKIDSS/UDS), and the Spitzer legacy survey of the UKIDSS/UDS. Among a total of 302 LAEs (224 for and 78 for ), only 11 are detected in the K band, i.e. brighter than mag. Eight of the 11 K-detected LAEs are spectroscopically confirmed. In our stellar population analysis, we treat K-detected objects individually, while K-undetected objects are stacked at each redshift. We find that the K-undetected objects, which should closely represent the LAE population as a whole, have low stellar masses of , modest star formation rates (SFRs) of , and modest dust extinction of . The K-detected objects are massive, , and have significant dust extinction with a median of . Four K-detected objects with the reddest spectral energy distributions, two of which are spectroscopically confirmed, are heavily obscured with , and their continua resemble those of some local ultraluminous infrared galaxies (ULIRGs). Interestingly, they have large Lyα equivalent widths ≃70–250 Å. If these four are excluded, our sample has a weak anticorrelation between Lyα equivalent width and Mstar. We compare the stellar masses and the specific SFRs (sSFRs) of LAEs with those of Lyman-break galaxies (LBGs), distant red galaxies, submillimetre galaxies, and I- or K-selected galaxies with photometric redshifts of . We find that the LAE population is the least massive among all the galaxy populations in question, but with relatively high sSFRs, while near-infrared (NIR)-detected LAEs have Mstar and sSFR similar to LBGs. Our reddest four LAEs have very high sSFRs in spite of large Mstar, thus occupying a unique region in the Mstar versus sSFR space. [ABSTRACT FROM AUTHOR]

We present new ALMA observations and physical properties of a Lyman break galaxy at z = 7.15. Our target, B14-65666, has a bright ultra-violet (UV) absolute magnitude, M UV ≈ −22.4, and has been spectroscopically identified in Lyα with a small rest-frame equivalent width of ≈4 Å. A previous Hubble Space TElescope (HST) image has shown that the target is composed of two spatially separated clumps in the rest-frame UV. With ALMA, we have newly detected spatially resolved [O  iii ] 88 μm, [C  ii ] 158 μm, and their underlying dust continuum emission. In the whole system of B14-65666, the [O  iii ] and [C  ii ] lines have consistent redshifts of 7.1520 ± 0.0003, and the [O  iii ] luminosity, (34.4 ± 4.1) × 108  L ⊙, is about three times higher than the [C  ii ] luminosity, (11.0 ± 1.4) × 108  L ⊙. With our two continuum flux densities, the dust temperature is constrained to be T d ≈ 50–60 K under the assumption of a dust emissivity index of βd = 2.0–1.5, leading to a large total infrared luminosity of L TIR ≈ 1 × 1012  L ⊙. Owing to our high spatial resolution data, we show that the [O  iii ] and [C  ii ] emission can be spatially decomposed into two clumps associated with the two rest-frame UV clumps whose spectra are kinematically separated by ≈200 km s−1. We also find these two clumps have comparable UV, infrared, [O  iii ], and [C  ii ] luminosities. Based on these results, we argue that B14-65666 is a starburst galaxy induced by a major merger. The merger interpretation is also supported by the large specific star formation rate (defined as the star formation rate per unit stellar mass), sSFR |$= 260^{+119}_{-57}\:$| Gyr−1, inferred from our SED fitting. Probably, a strong UV radiation field caused by intense star formation contributes to its high dust temperature and the [O  iii ]-to-[C  ii ] luminosity ratio. [ABSTRACT FROM AUTHOR]

We present ionizing spectra estimated at 13.6–100 eV for 10 dwarf galaxies with strong high-ionization lines of He ii λ 4686 and [Ne v ] λ 3426 ([Ne iv ] λ 2424) at z = 0 (z = 8) that are identified in our Keck/LRIS spectroscopy and the literature (the JWST Early Release Observations program). With the flux ratios of these high-ionization lines and >10 low-ionization lines of hydrogen, helium, oxygen, neon, and sulfur, we determine ionizing spectra consisting of stellar and nonthermal power-law radiation by photoionization modeling with free parameters of nebular properties, including metallicity and ionization parameter, canceling out abundance ratio differences. We find that all of the observed flux ratios are well reproduced by the photoionization models with the power-law index α EUV of α EUV ∼ (–1) − 0 and the luminosity L EUV of L EUV ∼ 1040–1042 erg s−1 at ∼55–100 eV for six galaxies, while four galaxies include large systematics in α EUV caused by stellar radiation contamination. We then compare α EUV and L EUV of these six galaxies with those predicted by the black hole (BH) accretion disk models and find that α EUV and L EUV are similar to those of the intermediate-mass BHs (IMBHs) in BH accretion disk models, albeit with possibilities of the other scenarios. Confirming these results with a known IMBH having a mass M BH of M BH = 105.75 M ⊙, we find that four local galaxies and one z = 7.665 galaxy have ionizing spectra consistent with those of IMBHs with M BH ∼ 103–105 M ⊙. [ABSTRACT FROM AUTHOR]

We present the statistics of faint submillimeter/millimeter galaxies (SMGs) and serendipitous detections of a submillimeter/millimeter line emitter (SLE) with no multi-wavelength continuum counterpart revealed by the deep ALMA observations. We identify faint SMGs with flux densities of 0.1-1.0 mJy in the deep Band-6 and Band-7 maps of 10 independent fields that reduce cosmic variance effects. The differential number counts at 1.2 mm are found to increase with decreasing flux density down to 0.1 mJy. Our number counts indicate that the faint (0.1-1.0 mJy, or SFRIR ∼ 30-300 M☼ yr–1) SMGs contribute nearly a half of the extragalactic background light (EBL), while the remaining half of the EBL is mostly contributed by very faint sources with flux densities of <0.1 mJy (SFRIR ≲ 30 M☼ yr–1). We conduct counts-in-cells analysis with multifield ALMA data for the faint SMGs, and obtain a coarse estimate of galaxy bias, bg < 4. The galaxy bias suggests that the dark halo masses of the faint SMGs are ≲ 7 × 1012M☼, which is smaller than those of bright (>1 mJy) SMGs, but consistent with abundant high-z star-forming populations, such as sBzKs, LBGs, and LAEs. Finally, we report the serendipitous detection of SLE-1, which has no continuum counterparts in our 1.2 mm-band or multi-wavelength images, including ultra deep HST/WFC3 and Spitzer data. The SLE has a significant line at 249.9 GHz with a signal-to-noise ratio of 7.1. If the SLE is not a spurious source made by the unknown systematic noise of ALMA, the strong upper limits of our multi-wavelength data suggest that the SLE would be a faint galaxy at z ≳ 6. [ABSTRACT FROM AUTHOR]

We have initiated a new survey for local extremely metal-poor galaxies (EMPGs) with Subaru/Hyper Suprime-Cam (HSC) large-area (∼500 deg2) optical images reaching a 5σ limit of ∼26 mag, about 100 times deeper than the Sloan Digital Sky Survey (SDSS). To select Z/Z⊙ < 0.1 EMPGs from ∼40 million sources detected in the Subaru images, we first develop a machine-learning (ML) classifier based on a deep neural network algorithm with a training data set consisting of optical photometry of galaxy, star, and QSO models. We test our ML classifier with SDSS objects having spectroscopic metallicity measurements and confirm that our ML classifier accomplishes 86% completeness and 46% purity EMPG classifications with photometric data. Applying our ML classifier to the photometric data of the Subaru sources, as well as faint SDSS objects with no spectroscopic data, we obtain 27 and 86 EMPG candidates from the Subaru and SDSS photometric data, respectively. We conduct optical follow-up spectroscopy for 10 of our EMPG candidates with Magellan/LDSS-3+MagE, Keck/DEIMOS, and Subaru/FOCAS and find that the 10 EMPG candidates are star-forming galaxies at z = 0.007–0.03 with large Hβ equivalent widths of 104–265 Å, stellar masses of log(/) = 5.0–7.1, and high specific star formation rates of ∼300 Gyr−1, which are similar to those of early galaxies at z ≳ 6 reported recently. We spectroscopically confirm that 3 out of 10 candidates are truly EMPGs with Z/Z⊙ < 0.1, one of which is HSC J1631+4426, the most metal-poor galaxy, with Z/Z⊙ = 0.016, ever reported. [ABSTRACT FROM AUTHOR]