Search

Galaxies are known to be aligned toward specific directions within the large-scale structure. Such alignment signals become important for controlling the systematics of weak lensing surveys and for constraining galaxy formation and evolution scenarios. We measure the galaxy-ellipticity and ellipticity-ellipticity correlation functions for blue star-forming galaxies at $z=1.19$ and $z=1.47$ that are selected by detecting [OII] emission lines in narrow-band filters of the Hyper Suprime-Cam on the Subaru Telescope. Assuming that disk galaxies are thin and rotation-supported, we also measure the spin correlation function by estimating spin directions with ellipticities and position angles. Above $1 \; h^{-1}{\rm Mpc}$, we do not find significant signals for galaxy-ellipticity, ellipticity-ellipticity, or spin correlations at both redshifts. Below $1 \; h^{-1}{\rm Mpc}$, a weak deviation from zero is seen at $z=1.47$, implying weak spin-filament correlations, but it is not verified by the direct comparison between angles of spins and filaments. The linear alignment model fit yields the amplitude parameter $A_{\rm NLA}=1.38\pm2.32$ at $z=1.19$ and $0.45\pm2.09$ at $z=1.47$ ($95\%$ confidence levels). We discuss various observational and physical origins that affect the search for alignments of disk galaxies at high redshifts., Comment: 16 pages, 12 figures, submitted to PASJ

We present new Atacama Large Millimeter/submillimeter Array (ALMA) results obtained from spatially resolved CO $J$=2-1 line ($0.4''$ resolution) and 870 $\mu$m continuum ($0.2''$ resolution) observations of cluster galaxies in XMMXCS J2215.9-1738 at $z=1.46$. Our sample comprises 17 galaxies within $\sim0.5$ Mpc ($0.6R_{200}$) of the cluster center, all of which have previously been detected in the CO $J$=2-1 line at a lower resolution. The effective radii of both the CO $J$=2-1 line and 870 $\mu$m dust continuum emissions are robustly measured for nine galaxies by modeling the visibilities. We find that the CO $J$=2-1 line emission in all of the nine galaxies is more extended than the dust continuum emission by a factor of $2.8\pm1.4$. We investigate the spatially resolved Kennicutt-Schmidt (KS) relation in two regions within the interstellar medium of the galaxies. The relation for our sample reveals that the central region ($0

This paper reports detections of H$\alpha$ emission and stellar continuum out to approximately 30 physical kpc, and H$\alpha$ directionality in the outskirts of H$\alpha$-emitting galaxies (H$\alpha$ emitters) at $z=0.4$. This research adopts narrow-band selected H$\alpha$ emitters at $z=0.4$ from the emission-line object catalog by Hayashi et al. (2020), which is based on data in the Deep and Ultradeep layers of the Hyper Suprime-Cam Subaru Strategic Program. Deep narrow- and broad-band images of 8625 H$\alpha$ emitters across 16.8 deg$^2$ enable us to construct deep composite emission-line and continuum images. The stacked images show diffuse H$\alpha$ emission (down to $\sim5\times10^{-20}$ erg~s$^{-1}$cm$^{-2}$arcsec$^{-2}$) and stellar continuum (down to $\sim5\times10^{-22}$ erg~s$^{-1}$cm$^{-2}$A$^{-1}$arcsec$^{-2}$), extending beyond 10 kpc at stellar masses $>10^9$ M$_\odot$, parts of which may originate from stellar halos. Those radial profiles are broadly consistent with each other. In addition, we obtain a dependence of the H$\alpha$ emission on the position angle because relatively higher H$\alpha$ equivalent width has been detected along the minor-axis towards galaxy disks. While the H$\alpha$ directionality could be attributed to biconical outflows, further research with hydrodynamic simulations is highly demanded to pin down the exact cause., Comment: 8 pages, 7 figures. Accepted for publication in Publications of the Astronomical Society of Japan (PASJ)

In a protocluster USS1558-003 at z=2.53, galaxies in the dense cores show systematically elevated star-forming activities than those in less dense regions. To understand its origin, we look into the gas properties of the galaxies in the dense cores by conducting deep 1.1mm observations with Atacama Large Millimeter/submillimeter Array (ALMA). We detect interstellar dust continuum emissions from 12 member galaxies and estimate their molecular gas masses. Comparing these gas masses with our previous measurements from CO(3-2) line, we infer that the latter might be overestimated. We find that the gas to stellar mass ratios of the galaxies in the dense cores tend to be higher (at M* ~ 10^{10} M_sun) where we see the enhanced star-forming activities), suggesting that such large gas masses can sustain their high star-forming activities. However, if we compare the gas properties of these protocluster galaxies with the gas scaling relations constructed for field galaxies at similar cosmic epoch, we find no significant environmental difference at the same stellar mass and star formation rate. Although both gas mass ratios and star-forming activities are enhanced in the majority of member galaxies, they appear to follow the same scaling relation as field galaxies. Our results are consistent with the scenario that the cold gas is efficiently supplied to protocluster cores and to galaxies therein along surrounding filamentary structures, which leads to the high gas mass fractions and thus the elevated star-formation activities, but without changing the star formation law., Comment: 18 pages, 10 figures, ApJ accepted

We perform a stacking analysis of the HI spectra from the Arecibo Legacy Fast ALFA (ALFALFA) survey for optically-selected local galaxies from the Sloan Digital Sky Survey (SDSS) to study the average gas fraction of galaxies at fixed stellar mass ($M_*$) and star formation rate (SFR). We first confirm that the average gas fraction strongly depends on the stellar mass and SFR of host galaxies; massive galaxies tend to have a lower gas fraction, and actively star-forming galaxies show higher gas fraction, which is consistent with many previous studies. Then we investigate the morphological dependence of the HI gas mass fraction at fixed $M_*$ and SFR to minimize the effects of these parameters. We use three morphological classifications based on parametric indicator (S\'{e}rsic index), non-parametric indicator (C-index), and visual inspection (smoothness from the Galaxy Zoo 2 project) on the optical image. We find that there is no significant morphological dependence of the HI gas mass fraction at fixed $M_*$ and SFR when we use C-index. In comparison, there exists a hint of diminishment in the HI gas mass fraction for "smooth" galaxies compared with "non-smooth" galaxies. We find that the visual smoothness is sensitive to the existence of small-scale structures in a galaxy. Our result suggests that even at fixed $M_*$ and SFR, the presence of such small-scale structures (seen in the optical image) is linked to their total HI gas content., Comment: 13 pages, 10 figures

We report the time variability of the late-time radio emission in a Type-I superluminous supernova (SLSN), PTF10hgi, at z = 0.0987. The Karl G. Jansky Very Large Array 3 GHz observations at 8.6 and 10 years after the explosion both detected radio emission with a ~40% decrease in flux density in the second epoch. This is the first report of a significant variability of the late-time radio light curve in a SLSN. Through combination with previous measurements in two other epochs, we constrained both the rise and decay phases of the radio light curve over three years, peaking at approximately 8-9 years after the explosion with a peak luminosity of L(3GHz) = 2 x 10^21 W/Hz. Possible scenarios for the origin of the variability are an active galactic nucleus (AGN) in the host galaxy, an afterglow caused by the interaction between an off-axis jet and circumstellar medium, and a wind nebula powered by a newly-born magnetar. Comparisons with models show that the radio light curve can be reproduced by both the afterglow model and magnetar wind nebula model. Considering the flat radio spectrum at 1-15 GHz and an upper limit at 0.6 GHz obtained in previous studies, plausible scenarios are a low-luminosity flat-spectrum AGN or a magnetar wind nebula with a shallow injection spectral index., Comment: 9 pages, 4 figures, accepted for publication in ApJ Letters

Subaru Strategic Program with the Hyper-Suprime Cam (HSC-SSP) has proven to be successful with its extremely-wide area coverage in past years. Taking advantages of this feature, we report initial results from exploration and research of expansive over- and under-dense structures at $z=$ 0.3-1 based on the second Public Data Release where optical 5-band photometric data for $\sim$ eight million sources with $i<23$ mag are available over $\sim360$ square degrees. We not only confirm known superclusters but also find candidates of titanic over- and under-dense regions out to $z=1$. The mock data analysis suggests that the density peaks would involve one or more massive dark matter haloes ($>10^{14}$ M$_\odot$) of the redshift, and the density troughs tend to be empty of massive haloes over $>10$ comoving Mpc. Besides, the density peaks and troughs at $z<0.6$ are in part identified as positive and negative weak lensing signals respectively, in mean tangential shear profiles, showing a good agreement with those inferred from the full-sky weak lensing simulation. The coming extensive spectroscopic surveys will be able to resolve these colossal structures in three-dimensional space. The number density information over the entire survey field will be available as grid-point data on the website of the HSC-SSP data release (https://hsc.mtk.nao.ac.jp/ssp/data-release/)., Comment: 22 pages, 23 figures, accepted for publication in MNRAS

We study the angular correlation function of star-forming galaxies and properties of their host dark matter halos at z>1 using the Hyper-Suprime Cam (HSC) SSP survey. We use [OII] emitters identified using two narrow-band (NB) filters, NB816 and NB921, in the Deep/UltraDeep layers, which respectively cover large angular areas of 16.3 deg^2 and 16.9 deg^2. Our sample contains 8302 and 9578 [OII] emitters at z=1.19 (NB816) and z=1.47 (NB921), respectively. We detect a strong clustering signal over a wide angular range, 0.001 < \theta < 1 [deg], with the bias $b=1.61^{+0.13}_{-0.11}$ (z=1.19) and $b=2.09^{+0.17}_{-0.15}$ (z=1.47). We also find a clear deviation of the correlation from a simple power-law form. To interpret the measured clustering signal, we adopt a halo occupation distribution (HOD) model that is constructed to explain the spatial distribution of galaxies selected by a star formation rate. The observed correlation function and number density are simultaneously explained by the best-fitting HOD model. From the constrained HOD model, the average mass of halos hosting the [OII] emitters is derived to be $\log{M_{eff}/(h^{-1}M_\odot)}=12.70^{+0.09}_{-0.07}$ and $12.61^{+0.09}_{-0.05}$ at z=1.19 and 1.47, respectively, which will become halos with the present-day mass, $M\sim 1.5 \times 10^{13}h^{-1}M_\odot$. The satellite fraction of the [OII] emitter sample is found to be $f_{sat}\sim 0.15$. All these values are consistent with the previous studies of similar samples, but we obtain tighter constraints even in a larger parameter space due to the larger sample size from the HSC. The results obtained for host halos of [OII] emitters in this paper enable the construction of mock galaxy catalogs and the systematic forecast study of cosmological constraints from upcoming emission line galaxy surveys such as the Subaru PFS survey., Comment: 21 pages, 13 figures, 5 tables, accepted to PASJ

We conducted sub-millimeter observations with the Atacama Large Millimeter/sub-millimeter Array (ALMA) of star-forming galaxies at $z\sim3.3$, whose gas-phase metallicities have been previously measured. We investigate the dust and gas contents of the galaxies at $z\sim3.3$ and study how galaxies are interacting with their circumgalactic/intergalactic medium at this epoch by probing their gas mass fractions and gas-phase metallicities. Single-band dust continuum emission tracing dust mass and the relation between the gas-phase metallicity and gas-to-dust mass ratio are used to estimate the gas masses. The estimated gas mass fractions and depletion timescales are $f_{\rm gas}=$ 0.20-0.75 and $t_{\rm dep}=$ 0.09-1.55 Gyr, respectively. Although the galaxies appear to tightly distribute around the star-forming main sequence at $z\sim3.3$, both quantities show a wider spread at a fixed stellar mass than expected from the scaling relation, suggesting a large diversity of fundamental gas properties among star-forming galaxies apparently on the main sequence. Comparing gas mass fraction and gas-phase metallicity between the star-forming galaxies at $z\sim3.3$ and at lower redshifts, star-forming galaxies at $z\sim3.3$ appear to be more metal-poor than local galaxies with similar gas mass fractions. Using the gas regulator model to interpret this offset, we find that it can be explained by a higher mass-loading factor, suggesting that the mass-loading factor in outflows increases at earlier cosmic times., Comment: 19 pages, 7 figures, 2 tables, Accepted for publication in ApJ

To determine the dominant sources for cosmic reionization, the evolution history of the global ionizing fraction, and the topology of the ionized regions, we have conducted a deep imaging survey using four narrow-band (NB) and one intermediate-band (IB) filters on the Subaru/Hyper Suprime-Cam (HSC), called Cosmic HydrOgen Reionization Unveiled with Subaru (CHORUS). The central wavelengths and full-widths-at-half-maximum of the CHORUS filters are, respectively, 386.2 nm and 5.5 nm for NB387, 526.0 nm and 7.9 nm for NB527, 717.1 nm and 11.1 nm for NB718, 946.2 nm and 33.0 nm for IB945, and 971.2 nm and 11.2 nm for NB973. This combination, including NB921 (921.5 nm and 13.5 nm) from the Subaru Strategic Program with HSC (HSC SSP), are carefully designed, as if they were playing a chorus, to observe multiple spectral features simultaneously, such as Lyman continuum, Ly$\alpha$, C~{\sc iv}, and He~{\sc ii} for $z=2$--$7$. The observing field is the same as that of the deepest footprint of the HSC SSP in the COSMOS field and its effective area is about 1.6 deg$^2$. Here, we present an overview of the CHORUS project, which includes descriptions of the filter design philosophy, observations and data reduction, multiband photometric catalogs, assessments of the imaging quality, measurements of the number counts, and example use cases of the data. All the imaging data, photometric catalogs, masked pixel images, data of limiting magnitudes and point spread functions, results of completeness simulations, and source number counts are publicly available through the HSC SSP database., Comment: 17 pages, 6 figures, PASJ open access (https://academic.oup.com/pasj/advance-article-abstract/doi/10.1093/pasj/psaa100/5959796), all the data products are available at https://hsc-release.mtk.nao.ac.jp/doc/index.php/chorus

We present the selection, spectroscopic identification, and physical properties of extreme emission line galaxies (EELGs) at $33$ with intense [OIII] emission, and H$\alpha$ emitters at $z\simeq 2$, respectively. These spectroscopically identified EELGs at $z\simeq 3.3$ show, on average, higher specific star formation rates (sSFR) than the star-forming main sequence, low dust attenuation of $E(B-V) \lesssim 0.1$ mag, and high [OIII]/[OII] ratios of $\gtrsim 3$. We also find that our EELGs at $z\simeq 3.3$ have higher hydrogen ionizing photon production efficiencies ($\xi_\mathrm{ion}$) than the canonical value ($\simeq 10^{25.2}$ Hz/erg), indicating that they are efficient in ionizing their surrounding interstellar medium. These physical properties suggest that they are low metallicity galaxies with higher ionization parameters and harder UV spectra than normal SFGs, which is similar to galaxies with Lyman continuum (LyC) leakage. Among our EELGs, those with the largest [OIII]/[OII] and EW([OIII]) values would be the most promising candidates to search for LyC leakage., Comment: 29 pages, 16 figures, 4 tables, accepted for publication in ApJ

We present 0.2arcsec-resolution Atacama Large Millimeter/submillimeter Array observations at 870 $\mu$m in a stellar mass-selected sample of 85 massive ($M_\mathrm{star}>10^{11}~M_\odot$) star-forming galaxies (SFGs) at z=1.9-2.6 in the 3D-HST/CANDELS fields of UDS and GOODS-S. We measure the effective radius of the rest-frame far-infrared (FIR) emission for 62 massive SFGs. They are distributed over wide ranges of FIR size from $R_\mathrm{e,FIR}=$0.4 kpc to $R_\mathrm{e,FIR}=$6 kpc. The effective radius of the FIR emission is smaller by a factor of 2.3$^{+1.9}_{-1.0}$ than the effective radius of the optical emission and by a factor of 1.9$^{+1.9}_{-1.0}$ smaller than the half-mass radius. Even with taking into account potential extended components, the FIR size would change by ~10%. By combining the spatial distributions of the FIR and optical emission, we investigate how galaxies change the effective radius of the optical emission and the stellar mass within a radius of 1 kpc, $M_\mathrm{1kpc}$. The compact starburst puts most of massive SFGs on the mass--size relation for quiescent galaxies (QGs) at z~2 within 300 Myr if the current star formation activity and its spatial distribution are maintained. We also find that within 300 Myr, ~38% of massive SFGs can reach the central mass of $M_\mathrm{1kpc}=10^{10.5}~M_\odot$, which is around the boundary between massive SFGs and QGs. These results suggest an outside-in transformation scenario in which a dense core is formed at the center of a more extended disk, likely via dissipative in-disk inflows. Synchronized observations at ALMA 870 $\mu$m and JWST 3-4 $\mu$m will explicitly verify this scenario., Comment: 25 pages, 15 figures, 3 tables, accepted for publication in ApJ

We have conducted a comprehensive survey of emission-line galaxies at $z\lesssim1.6$ based on narrowband (NB) imaging data taken with Hyper Suprime-Cam (HSC) on the Subaru telescope. In this paper, we update the catalogs of H$\alpha$, [OIII], and [OII] emission-line galaxies using the data from the second Public Data Release (PDR2) of Subaru Strategic Program (SSP) of HSC and Cosmic HydrOgen Reionization Unveiled with Subaru (CHORUS) survey along with the spectroscopic redshifts for 2,019 emission-line galaxies selected with the PDR1 data. The wider effective coverage of NB816 and NB921, 16.3 deg$^2$ and 16.9 deg$^2$ respectively, are available in the Deep and UltraDeep layers of HSC-SSP from the PDR2. The CHORUS survey provides us with data with additional three NBs (NB527, NB718, and NB973) in the COSMOS field in the UltraDeep layer (1.37 deg$^2$). The five NB datasets allow us to investigate the star-forming galaxies presenting emission-lines at 14 specific redshifts ranging from $z\sim1.6$ down to $z\sim0.05$. We revisit the distribution of large-scale structures and luminosity functions (LFs) for the emission-line galaxies with the large samples of 75,377 emission-line galaxies selected. The redshift revolution of LFs shows that the star formation rate densities (SFRDs) decreases monotonically from $z\sim1.6$, which is consistent with the cosmic SFRD ever known. Our samples of emission-line galaxies covering a sufficiently large survey volume are useful to investigate the evolution of star-forming galaxies since the cosmic noon in a wide range of environments including galaxy clusters, filaments, and voids., Comment: 32 pages, 23 figures, 6 tables, accepted for publication in PASJ. The catalog of emission-line galaxies from HSC-SSP PDR2 data will be available soon at https://hsc-release.mtk.nao.ac.jp/, and the catalog from CHORUS data will be available after the CHORUS data are publicly released

We report an automated morphological classification of galaxies into S-wise spirals, Z-wise spirals, and non-spirals using big image data taken from Subaru/Hyper Suprime-Cam (HSC) Survey and a convolutional neural network(CNN)-based deep learning technique. The HSC i-band images are about 25 times deeper than those from the Sloan Digital Sky Survey (SDSS) and have a two times higher spatial resolution, allowing us to identify substructures such as spiral arms and bars in galaxies at z>0.1. We train CNN classifiers by using HSC images of 1447 S-spirals, 1382 Z-spirals, and 51,650 non-spirals. As the number of images in each class is unbalanced, we augment the data of spiral galaxies by horizontal flipping, rotation, and rescaling of images to make the numbers of three classes similar. The trained CNN models correctly classify 97.5% of the validation data, which is not used for training. We apply the CNNs to HSC images of a half million galaxies with an i-band magnitude of i<20 over an area of 320 deg^2. 37,917 S-spirals and 38,718 Z-spirals are identified, indicating no significant difference between the numbers of two classes. Among a total of 76,635 spiral galaxies, 48,576 are located at z>0.2, where we are hardly able to identify spiral arms in the SDSS images. Our attempt demonstrates that a combination of the HSC big data and CNNs has a large potential to classify various types of morphology such as bars, mergers and strongly-lensed objects., Comment: 12 pages, 10 figures, 3 tables, accepted for publication in MNRAS

Galaxies change their properties as they assemble into clusters. In order to understand the physics behind that, we need to go back in time and observe directly what is occurring in galaxies as they fall into a cluster. We have conducted a narrow-band and $J$-band imaging survey on a cluster CL1604-D at $z=0.923$ using a new infrared instrument SWIMS installed at the Subaru Telescope. The narrow-band filter, NB1261, matches to H$\alpha$ emission from the cluster at $z=0.923$. Combined with a wide range of existing data from various surveys, we have investigated galaxy properties in and around this cluster in great detail. We have identified 27 H$\alpha$ emitters associated with the cluster. They have significant overlap with MIPS 24$\mu$m sources and are located exclusively in the star forming regime on the rest-frame $UVJ$ diagram. We have identified two groups of galaxies near the cluster in the 2D spatial distribution and the phase-space diagram, which are likely to be in-falling to the cluster main body. We have compared various physical properties of star forming galaxies, such as specific star formation rates (burstiness) and morphologies (merger) as a function of environment; cluster center, older group, younger group, and the field. As a result, a global picture has emerged on how the galaxy properties are altered as they assemble into a denser region. This includes the occurrence of mergers, enhancement of star formation activity, excursion to the dusty starburst phase, and eventual quenching to a passive phase., Comment: 19 pages, 15 figures. Accepted for publication in ApJ. Error bars in Table 2 corrected

We present element abundance ratios and ionizing radiation of local young low-mass (~$10^{6}$ M_sun) extremely metal poor galaxies (EMPGs) with a 2% solar oxygen abundance (O/H)_sun 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 [FeIII]4658 and HeII4686 are detected in very deep optical spectra of the EMPGs taken with 8m-class telescopes including Keck and Subaru (Kojima et al. 2019, Izotov et al. 2018), enabling us to derive element abundance ratios with photoionization models. We find that neon- 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)_sun 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)_sun, which are unlikely 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, these EMPGs have very high HeII4686/H$\beta$ ratios of ~1/40, which are not reproduced by existing models of high-mass X-ray binaries whose progenitor stellar masses are less than 120 M_sun. 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 HeII4686/H$\beta$ ratios are explained by the past existence of super massive ($>$300 M_sun) stars, which may evolve into intermediate-mass black holes ($\gtrsim$100 M_sun)., Comment: ApJ in press. 23 pages, 7 Figures, 6 Tables

We present the results of CO(1-0) observations of the host galaxy of a Type I superluminous supernova (SLSN-I), SN2017egm, one of the closest SLSNe-I at z = 0.03063, by using the Atacama Large Millimeter/submillimeter Array. The molecular gas mass of the host galaxy is $M_{\rm gas} = (4.8 \pm 0.3) \times 10^9$ $M_{\odot}$, placing it on the sequence of normal star-forming galaxies in an $M_{\rm gas}$-star-formation rate (SFR) plane. The molecular hydrogen column density at the location of SN2017egm is higher than that of the Type II SN PTF10bgl, which is also located in the same host galaxy, and those of other Type II and Ia SNe located in different galaxies, suggesting that SLSNe-I have a preference for a dense molecular gas environment. On the other hand, the column density at the location of SN2017egm is comparable to those of Type Ibc SNe. The surface densities of molecular gas and the SFR at the location of SN2017egm are consistent with those of spatially resolved local star-forming galaxies and follow the Schmidt-Kennicutt relation. These facts suggest that SLSNe-I can occur in environments with the same star-formation mechanism as in normal star-forming galaxies., Comment: 6 pages, 5 figures, accepted for publication in PASJ

We construct a model of H$\alpha$ emitters (HAEs) based on a semi-analytic galaxy formation model, the New Numerical Galaxy Catalog ($\nu^2$GC). In this paper, we report our estimate for the field variance of the HAE distribution. By calculating the H$\alpha$ luminosity from the star-formation rate of galaxies, our model well reproduces the observed H$\alpha$ luminosity function (LF) at $z=0.4$. The large volume of the $\nu^2$GC makes it possible to examine the spatial distribution of HAEs over a region of (411.8 Mpc)$^3$ in the comoving scale. The surface number density of $z=0.4$ HAEs with $L_{\rm H\alpha} \geq 10^{40}$ erg s$^{-1}$ is 308.9 deg$^{-2}$. We have confirmed that the HAE is a useful tracer for the large-scale structure of the Universe because of their significant overdensity ($>$ 5$\sigma$) at clusters and the filamentary structures. The H$\alpha$ LFs within a survey area of $\sim$2 deg$^2$ (typical for previous observational studies) show a significant field variance up to $\sim$1 dex. Based on our model, one can estimate the variance on the H$\alpha$ LFs within given survey areas., Comment: 13 pages, 11 figures, accepted for publication in the ApJ

We have initiated a new survey for local extremely metal-poor galaxies (EMPGs) with Subaru/Hyper Suprime-Cam (HSC) large-area (~500 deg^2) optical images reaching a 5 sigma limit of ~26 magnitude, about 100 times deeper than the Sloan Digital Sky Survey (SDSS). To select Z/Z_sun<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 out 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 H_beta equivalent widths of 104-265 A, stellar masses of log(M*/M_sun)=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_sun<0.1, one of which is HSC J1631+4426, the most metal-poor galaxy with Z/Z_sun=0.016 reported ever., Comment: 30 pages, 26 figures, and 8 tables; (Revision: metallicities changed due to the use of a more pricise dust correction method, but conclusion does not change, Minor: a table, some figures, and sentences are added for a clear explanation.)

We investigate the molecular gas in, and star-formation properties of, the host galaxy (CGCG 137-068) of a mysterious transient, AT2018cow, at kpc and larger scales, using archival band-3 data from the Atacama Large Millimeter/submillimeter Array (ALMA). AT2018cow is the nearest Fast-Evolving Luminous Transient (FELT), and this is the very first study unveiling molecular-gas properties of FELTs. The achieved rms and beam size are 0.21 mJy beam$^{-1}$ at a velocity resolution of $40$ km s$^{-1}$ and $3".66\times2".71$ ($1.1~{\rm kpc} \times 0.8~{\rm kpc}$), respectively. CO($J$=1-0) emission is successfully detected. The total molecular gas mass inferred from the CO data is $(1.85\pm0.04)\times10^8$ M$_\odot$ with the Milky Way CO-to-H$_2$ conversion factor. The H$_2$ column density at the AT2018cow site is estimated to be $8.6\times10^{20}$ cm$^{-2}$. The ALMA data reveal that (1) CGCG 137-068 is a normal star-forming (SF) dwarf galaxy in terms of its molecular gas and star-formation properties and (2) AT2018cow is located between a CO peak and a blue star cluster. These properties suggest on-going star formation and favor the explosion of a massive star as the progenitor of AT2018cow. We also find that CGCG 137-068 has a solar or super-solar metallicity. If the metallicity of the other FELT hosts is not higher than average, then some property of SF dwarf galaxies other than metallicity may be related to FELTs., Comment: 8 pages, 3 figures, 2 tables, accepted for publication in ApJL

We present the large-scale structure over more than 50 comoving Mpc scale at z $\sim$ 0.9 where the CL1604 supercluster, which is one of the largest structures ever known at high redshifts, is embedded. The wide-field deep imaging survey by the Subaru Strategic Program with Hyper Suprime-Cam reveals that the already-known CL1604 supercluster is a mere part of larger-scale structure extending to both the north and the south. We confirm that there are galaxy clusters at three slightly different redshifts in the northern and southern sides of the supercluster by determining the redshifts of 55 red-sequence galaxies and 82 star-forming galaxies in total by the follow-up spectroscopy with Subaru/FOCAS and Gemini-N/GMOS. This suggests that the structure ever known as the CL1604 supercluster is the tip of the iceberg. We investigate stellar population of the red-sequence galaxies using 4000 A break and Balmer H$\delta$ absorption line. Almost all of the red-sequence galaxies brighter than 21.5 mag in $z$-band show an old stellar population with $\gtrsim2$ Gyr. The comparison of composite spectra of the red-sequence galaxies in the individual clusters show that the galaxies at a similar redshift have similar stellar population age, even if they are located $\sim$50 Mpc apart from each other. However, there could be a large variation in the star formation history. Therefore, it is likely that galaxies associated with the large-scale structure at 50 Mpc scale formed at almost the same time, have assembled into the denser regions, and then have evolved with different star formation history along the hierarchical growth of the cosmic web., Comment: 21 pages, 9 figures, 5 tables, accepted for publication in PASJ

We present the results of our near-infrared (NIR) spectroscopic observations of a rich cluster candidate around a radio galaxy at $z=1.52$ (4C65.22) with Subaru/MOIRCS and LBT/LUCI. We observed 71 galaxies mostly on the star-forming main sequence selected by our previous broad-band (photo-$z$) and narrow-band H$\alpha$ imaging observation in this cluster environment. We successfully confirmed the redshifts of 39 galaxies, and conclude that this is a gravitationally bound, real cluster at $z=1.517$. Our spectroscopic data also suggest a hint of large-scale filaments or sheet-like three-dimensional structures crossing at the highest-density cluster core. By stacking the spectra to derive their average interstellar medium (ISM) gas-phase metallicity based on the [NII]/H$\alpha$ emission line flux ratio, we find that the mass-metallicity relation (MZR) in the 4C65.22 cluster environment is consistent with that of H$\alpha$-selected field galaxies at similar redshifts. Our results suggest that the environmental impacts on the MZR is small at high redshifts, but a larger sample of high-$z$ clusters and their member galaxies is still required to fully address the effect of environment as well as its cluster-cluster variation., Comment: 14 pages, 6 figures

At $z\sim2$, star-formation activity is thought to be high even in high-density environments such as galaxy clusters and proto-clusters. One of the critical but outstanding issues is if structural growth of star-forming galaxies can differ depending on their surrounding environments. In order to investigate how galaxies grow their structures and what physical processes are involved in the evolution of galaxies, one requires spatially resolved images of not only stellar components but also star-forming regions within galaxies. We conducted the Adaptive Optics(AO)-assisted imaging observations for star-forming galaxies in a dense proto-cluster core at $z=2.53$ with IRCS and AO188 mounted on the Subaru Telescope. A combination of AO and narrow-band filters allows us to obtain resolved maps of H$\alpha$-emitting regions with an angular resolution of 0.1--0.2~arcsec, which corresponds to $\sim1$ kpc at $z\sim2.5$. Based on stacking analyses, we compare radial profiles of star-forming regions and stellar components and find that the star-forming region of a sub-sample with $\rm log(M_*/M_\odot)\sim10-11$ is more extended than the stellar component, indicating the inside-out growth of the structure. This trend is similar to the one for star-forming galaxies in general fields at $z=2-2.5$ obtained with the same observational technique. Our results suggest that the structural evolution of star-forming galaxies at $z=2-2.5$ is mainly driven by internal secular processes irrespective of surrounding environments., Comment: 13 pages, 7 figures, 2 tables, Accepted for publication in PASJ

Recent simulations predict that the presence of stellar bulge suppress the efficiency of star formation in early-type galaxies, and this `morphological quenching' scenario is supported by many observations. In this study, we discuss the net effect of galaxy morphologies on the star formation efficiency (SFE) during the phase of galaxy transition, on the basis of our CO($J=1-0$) observations of 28 local `green-valley' galaxies with the Nobeyama 45m Radio Telescope. We observed 13 `disk-dominated' and 15 `bulge-dominated' green-valley galaxies at fixed stellar mass ($M_*$) and star formation rate (SFR), supplemented by 1 disk- and 6 bulge-dominated galaxies satisfying the same criteria from the xCOLD~GASS survey. By using a total of 35 green-valley galaxies, we reveal that the distributions of molecular gas mass, molecular gas fraction, and SFE of green-valley galaxies do not change with their morphologies, suggesting little impact of galaxy morphologies on their SFE, and interestingly this result is also valid for normal star-forming galaxies on the SF main-sequence selected from the xCOLD~GASS galaxies. On the other hand, we find that $\sim$20 % of bulge-dominated green-valley galaxies do not show significant CO emission line, showing high SFEs for their M$_*$ and SFR. These molecular gas deficient sources identified only in the bulge-dominated green-valley galaxies may represent an important population during the quenching phase under the influence of stellar bulge, but our results suggest that the presence of stellar bulge does not decrease the efficiency of on-going star formation, in contrast to the prediction of the morphological quenching scenario., Comment: 16 pages, 11 figures, accepted for publication in ApJ

We present the results from ALMA CO(3-2) observations of 66 Halpha-selected galaxies in three protoclusters around radio galaxies, PKS1138-262 (z=2.16) and USS1558-003 (z=2.53), and 4C23.56 (z=2.49). The pointing areas have an overdensity of ~100 compared to a mean surface number density of galaxies in field environments. We detect CO emission line in 16 star-forming galaxies, including previously published six galaxies, to measure the molecular gas mass. In the stellar mass range of 10.511.0 are comparable in mass to the scaling relation, or smaller. Our results suggest that the environmental effects on gas properties are mass-dependent: in high-density environments, gas accretion through cosmic filaments is accelerated in less massive galaxies while this is suppressed in the most massive system., Comment: 11 pages, 5 figures, 2 tables, accepted in Publications of the Astronomical Society of Japan (PASJ)

We present multi-wavelength studies of optically-defined merging clusters, based on the Hyper Suprime-Cam Subaru Strategic Program. Luminous red galaxies, tracing cluster mass distributions, enable to identify cluster subhalos at various merging stages, and thus make a homogeneous sample of cluster mergers, which is unbiased with respect to the merger boost of the intracluster medium (ICM). We define, using a peak-finding method, merging clusters with multiple-peaks and single clusters with single-peaks from the CAMIRA cluster catalog. Stacked weak-lensing analysis indicates that our sample of the merging clusters is categorized into major mergers. The average halo concentration for the merging clusters is $\sim70\%$ smaller than that of the single-peak clusters, which agrees well with predictions of numerical simulations. The spatial distribution of subhalos is less centrally concentrated than the mass distribution of the main halo. The fractions of red galaxies in the merging clusters are not higher than those of the single-peak clusters. We find a signature of the merger boost of the ICM from stacked Planck Sunyaev-Zeldovich effect and ROSAT X-ray luminosity, but not in optical richness. The stacked X-ray surface brightness distribution, aligned with the main-subhalo pairs of low redshift and massive clusters, shows that the central gas core is elongated along the merger axis and overall gas distribution is misaligned by $\sim60$ deg. The homogeneous, unbiased sample of cluster mergers and multi-wavelength follow-up studies provide a unique opportunity to make a complete picture of merger physics over the whole process., Comment: 23 pages, 10 figures, 1 table : accepted for the publication in PASJ

This paper is the second in a series presenting the results of our deep H$\alpha$-line survey towards protoclusters at $z>2$, based on narrow-band imaging with the Subaru Telescope. This work investigates massive galaxies in a protocluster region associated with a radio galaxy (PKS 1138$-$262), the Spiderweb galaxy, at $z=2.2$. Our 0.5 mag deeper narrow-band imaging than previous surveys collects a total of 68 H$\alpha$ emitters (HAE). 17 out of the 68 are newly discovered protocluster members. First, a very high characteristic stellar mass of M$_\star^\ast=10^{11.73}$ M$_\odot$ is measured from a Schechter function fit to the mass distribution of HAEs. Together with the Chandra X-ray data, we find that four out of six massive HAEs (M$_\star>10^{11}$ M$_\odot$) show bright X-ray emission, suggesting that they host active galactic nuclei (AGNs). Their mass estimates, therefore, would be affected by the nuclear emission from AGNs. Notably, the X-ray detected HAEs are likely positioned near the boundary between star-forming and quiescent populations in the rest-frame $UVJ$ plane. Moreover, our deep narrow-band data succeed in probing the bright H$\alpha$ (+[Nii]) line nebula of the Spiderweb galaxy extending over $\sim100$ physical kpc. These results suggest that the massive galaxies in the Spiderweb protocluster are on the way to becoming the bright red sequence objects seen in local galaxy clusters, where AGNs might play an essential role in their quenching processes. Though a more statistical database is needed to build a general picture., Comment: 22 pages, 17 figures, accepted for publication in the MNRAS

As a science verification study of the newly released AKARI/FIS Faint Source Catalog ver.1, this paper discusses the different levels of dust attenuation toward stellar light and nebular emission lines within local star-forming galaxies at 0.022,000 sources), we compare the dust attenuation levels toward stellar light (from L(IR)/L(UV) ratio) and nebular emission lines (from H-alpha/H-beta ratio). We find that there is a clear trend that more massive galaxies tend to have higher "extra" attenuation toward nebular regions, while galaxies with higher specific star formation rates tend to have lower extra attenuation. We also confirm these trends by using the WISE mid-infrared photometry with a significantly large sample size of the WISE-SDSS-GALEX galaxies (>50,000 sources). Finally, we study how the levels of extra attenuation toward nebular regions change across the SFR-Mstar plane. We find that, even at a fixed stellar mass, galaxies located below the main sequence tend to have higher levels of extra attenuation toward nebular regions, suggesting the change in dust geometry within the galaxies across the star-forming main sequence during the course of star formation quenching process., Comment: 14 pages, 14 figures, accepted for publication in PASJ AKARI Special Issue

The incidence of Active Galactic Nuclei (AGN) with local environment is a potentially valuable probe of the mechanisms that trigger and provide fuel for accretion onto supermassive black holes. While the correlation between AGN fraction and environment has been well-studied in the local universe, AGN fractions have been measured for relatively few dense environments at high redshift. In this paper we present a measurement of the X-ray AGN fraction in the USS 1558-003 protocluster associated with the z=2.53 radio galaxy 4C-00.62. Our measurement is based on a 100ks Chandra observation, follow-up spectroscopy from the Multi-Object Double Spectrograph on the Large Binocular Telescope, and broad and narrow band photometry. These data are sensitive to AGN more luminous than $L_{X}>2\times10^{43}$ erg s$^{-1}$ in the rest-frame hard X-ray band (2-10 keV). We have identified two X-ray AGN at the redshift of USS 1558-003, one of which is the radio galaxy. We have determined that $2.0^{+2.6}_{-1.3}$% of the H$\alpha$ emitters in the protocluster are X-ray AGN. Unlike most other high-redshift cluster progenitors studied with similar techniques, USS 1558-003 does not have a significantly higher fraction of AGN than field galaxies at similar redshifts. This lower AGN fraction is inconsistent with the expectation that the higher gas fractions at high redshift, combined with the high galaxy densities and modest relative velocities in protoclusters, should produce higher AGN fractions., Comment: 8 pages, 3 figures, submitted to ApJ

We present molecular gas reservoirs of eighteen galaxies associated with the XMMXCS J2215.9-1738 cluster at z=1.46. From Band 7 and Band 3 data of the Atacama Large Millimeter/submillimeter Array (ALMA), we detect dust continuum emission at 870 um and CO J=2-1 emission line from 8 and 17 member galaxies respectively within a cluster-centric radius of $R_{200}$. The molecular gas masses derived from the CO and/or dust continuum luminosities show that the fraction of molecular gas mass and the depletion time scale for the cluster galaxies are larger than expected from the scaling relations of molecular gas on stellar mass and offset from the main sequence of star-forming galaxies in general fields. The galaxies closer to the cluster center in terms of both projected position and accretion phase seem to show a larger deviation from the scaling relations. We speculate that the environment of galaxy cluster helps feed the gas through inflow to the member galaxies and also reduce the efficiency of star formation. The stacked Band 3 spectrum of 12 quiescent galaxies with stellar mass $\sim10^{11}$ M$_\odot$ within 0.5$R_{200}$ shows no detection of CO emission line, giving the upper limit of molecular gas mass and molecular gas fraction to be $<10^{10}$ M$_\odot$ and $<10$%, respectively. Therefore, the massive galaxies in the cluster core quench the star formation activity while consuming most of the gas reservoirs., Comment: 14 pages, 9 figures, 3 tables, accepted for publication in the ApJ

We combined deep U-band imaging from the KPNO-4m/MOSAIC camera with very deep multi-waveband data from the optical to infrared, to select Lyman Break Galaxies (LBGs) at z~3 using U-V and V-R colors in the Subaru Deep Field. With the resulting sample of 5161 LBGs, we construct the UV luminosity function down to $M_{UV} = -18$ and find a steep faint-end slope of $\alpha=-1.78 \pm 0.05$. We analyze rest-frame UV-to-IR spectral energy distributions generated from the median optical photometry and photometry on median-stacked IR images. In the stacks of faint LBGs, we find a background depression centered on the galaxy. This deficit results from the systematic difficulty of SExtractor in finding faint galaxies in regions with higher-than-average surface densities of foreground galaxies. We corrected our stacked magnitudes for this. Best-fit stellar population templates for the stacked LBG SEDs indicate stellar masses and star-formation rates of log M*/Msun = 10 and 50 M$_\odot$/yr at i' = 24, down to log M*/Msun = 8 and = 3 M$_\odot$/yr at i' = 27. For the faint stacked LBGs there is a 1-mag excess over the expected stellar continuum in the K-band, which we attribute to redshifted [OIII]4959+5007 and H$\beta$ lines. Their implied equivalent widths increase with decreasing mass, reaching $\rm{EW_0([O III]4959,5007+H\beta)}$ =1500A in the faintest bin. Such strong [OIII] emission is seen only in a miniscule fraction of the most extreme local emission-line galaxies, but it probably universal in the faint galaxies that reionized the universe. Finally, we analyze clustering by computing the angular correlation function and performing halo occupation distribution (HOD) analysis. We find a mean dark halo mass of log(Mhalo/h) Msun = 11.29$\pm 0.12$ for the full sample of LBGs, and log(Mhalo/h) Msun = 11.49$\pm 0.1$ for the brightest half., Comment: scheduled for publication in The Astrophysical Journal, 2017, 21 pages in preprint format (19 journal pages)

We present new results from near-infrared spectroscopy with Keck/MOSFIRE of [OIII]-selected galaxies at $z\sim3.2$. With our $H$ and $K$-band spectra, we investigate the interstellar medium (ISM) conditions, such as ionization states and gas metallicities. [OIII] emitters at $z\sim3.2$ show a typical gas metallicity of $\mathrm{12+log(O/H) = 8.07\pm0.07}$ at $\mathrm{log(M_*/M_\odot) \sim 9.0-9.2}$ and $\mathrm{12+log(O/H) = 8.31\pm0.04}$ at $\mathrm{log(M_*/M_\odot) \sim 9.7-10.2}$ when using the empirical calibration method. We compare the [OIII] emitters at $z\sim3.2$ with UV-selected galaxies and Ly$\alpha$ emitters at the same epoch and find that the [OIII]-based selection does not appear to show any systematic bias in the selection of star-forming galaxies. Moreover, comparing with star-forming galaxies at $z\sim2$ from literature, our samples show similar ionization parameters and gas metallicities as those obtained by the previous studies using the same calibration method. We find no strong redshift evolution in the ISM conditions between $z\sim3.2$ and $z\sim2$. Considering that the star formation rates at a fixed stellar mass also do not significantly change between the two epochs, our results support the idea that the stellar mass is the primary quantity to describe the evolutionary stages of individual galaxies at $z>2$., Comment: 20 pages, 11 figures, Accepted for publication in ApJ

We present the molecular gas mass fraction ($f_\mathrm{H_2}$) and star-formation efficiency (SFE) of local galaxies on the basis of our new CO($J=1-0$) observations with the Nobeyama 45m radio telescope, combined with the COLDGASS galaxy catalog, as a function of galaxy environment defined as the local number density of galaxies measured with SDSS DR7 spectroscopic data. Our sample covers a wide range in the stellar mass and SFR, and covers wide environmental range over two orders of magnitude. This allows us to conduct the first, systematic study of environmental dependence of molecular gas properties in galaxies from the lowest- to the highest-density environments in the local universe. We confirm that both $f_\mathrm{H_2}$ and SFE have strong positive correlations with the SFR offset from the star-forming main sequence ($\Delta$MS), and most importantly, we find that these correlations are universal across all environments. Our result demonstrates that star-formation activity within individual galaxies is primarily controlled by their molecular gas content, regardless of their global environment. Therefore, we claim that one always needs to be careful about the $\Delta$MS distribution of the sample when investigating the environmental effects on the H$_2$ gas content in galaxies., Comment: 12 pages, 7 figures, accepted for publication in ApJ

We carried out deep H$\alpha$ narrowband imaging with 10 hours net integrations towards the young protocluster, USS1558$-$003 at $z=2.53$ with the Subaru Telescope. This system is composed of four dense groups with massive local overdensities, traced by 107 H$\alpha$ emitters (HAEs) with stellar masses and dust-corrected star formation rates down to $1\times10^8$ M$_\odot$ and 3 M$_\odot$yr$^{-1}$, respectively. We have investigated the environmental dependence of various physical properties within the protocluster by comparing distributions of HAEs in higher and lower densities with a standard Kolmogorov--Smirnov test. At 97\% confidence level, we find enhanced star formation across the star-forming main sequence of HAEs living in the most extreme `supergroup', corresponding to the top quartile of overdensities. Furthermore, we derive distribution functions of H$\alpha$ luminosity and stellar mass in group and intergroup regions, approximately corresponding to 30 times and 8 times higher densities than the general field. As a consequence, we identify by 0.7 and 0.9 dex higher cutoffs in H$\alpha$ luminosity and stellar mass functions in the dense groups, respectively. On the other hand, HAEs in the intergroup environment of the protocluster show similar distribution functions to those of field galaxies despite residing in significant overdensities. In the early phase of cluster formation, as inferred from our results, the densest parts in the protocluster have had an accelerated formation of massive galaxies. We expect that these eventually grow and transform into early-type galaxies at the bright end of the red sequence as seen in present-day rich clusters of galaxies., Comment: Accepted for publication in MNRAS, 24 pages, 17 figures, 5 tables

We report a survey of molecular gas in galaxies in the XMMXCS J2215.9-1738 cluster at $z=1.46$. We have detected emission lines from 17 galaxies within a radius of $R_{200}$ from the cluster center, in Band 3 data of the Atacama Large Millimeter/submillimeter Array (ALMA) with a coverage of 93 -- 95 GHz in frequency and 2.33 arcmin$^2$ in spatial direction. The lines are all identified as CO $J$=2--1 emission lines from cluster members at $z\sim1.46$ by their redshifts and the colors of their optical and near-infrared (NIR) counterparts. The line luminosities reach down to $L'_{\rm CO(2-1)}=4.5\times10^{9}$ K km s$^{-1}$ pc$^2$. The spatial distribution of galaxies with a detection of CO(2--1) suggests that they disappear from the very center of the cluster. The phase-space diagram showing relative velocity versus cluster-centric distance indicates that the gas-rich galaxies have entered the cluster more recently than the gas-poor star-forming galaxies and passive galaxies located in the virialized region of this cluster. The results imply that the galaxies have experienced ram-pressure stripping and/or strangulation during the course of infall towards the cluster center and then the molecular gas in the galaxies at the cluster center is depleted by star formation., Comment: 7 pages, 4 figures, 1 table, accepted for publication in the ApJ Letters

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 (NB) imaging. The first Public Data Release (PDR1) provides us with data from two NB filters, specifically NB816 and NB921 over 5.7 deg$^2$ and 16.2 deg$^2$ respectively. The $5 \sigma$ limiting magnitudes are 25.2 (UDeep layer, 1.4 deg$^2$) and 24.8 (Deep layer, 4.3 deg$^2$) mag in NB816, and 25.1 (UDeep, 2.9 deg$^2$) and 24.6--24.8 (Deep, 13.3 deg$^2$) mag in NB921. The wide-field imaging allows us to construct unprecedentedly large samples of 8,054 H$\alpha$ emitters at z ~ 0.25 and 0.40, 8,656 [OIII] emitters at z ~ 0.63 and 0.84, and 16,877 [OII] 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 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 $>5\times10^5$ Mpc$^3$ 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$\alpha$ 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 NB data from the HSC-SSP to investigate star-forming galaxies at z<1.5., Comment: 28 pages, 22 figures, 5 tables, accepted for publication in PASJ (Subaru HSC-SSP special issue), The catalogs will be available at https://hsc-release.mtk.nao.ac.jp/

We present the environmental dependence of colour, stellar mass, and star formation (SF) activity in H-alpha-selected galaxies along the large-scale structure at z=0.4 hosting twin clusters in DEEP2-3 field, discovered by Subaru Strategic Programme of Hyper Suprime-Cam (HSC SSP). By combining photo-z selected galaxies and H-alpha emitters selected with broad-band and narrow-band (NB) data of the recent data release of HSC SSP (DR1), we confirm that galaxies in higher-density environments or galaxies in the cluster central regions show redder colours. We find that there still remains a possible colour-density and colour-radius correlation even if we restrict the sample to H-alpha-selected galaxies, likely due to the presence of massive H-alpha emitters in denser regions. We also find a hint of increased star formation rates (SFR) amongst H-alpha emitters towards the highest-density environment, again primarily driven by the excess of red/massive H-alpha emitters in high-density environment, while their specific SFR does not significantly change with environment. This work demonstrates the power of the HSC SSP NB data to study SF galaxies across environment in the distant universe., Comment: 15 pages, 11 figures, accepted for publication in PASJ (Subaru HSC-SSP special issue)

We present spatially resolved ALMA observations of the CO J=3-2 emission line in two massive galaxies at z=2.5 on the star-forming main sequence. Both galaxies have compact dusty star-forming cores with effective radii of Re=1.3 kpc and Re=1.2 kpc in the 870 um continuum emission. The spatial extent of star-forming molecular gas is also compact with Re=1.9 kpc and Re=2.3 kpc, but more extended than the dust emission. Interpreting the observed position-velocity diagrams with dynamical models, we find the starburst cores to be rotation-dominated with the ratio of the maximum rotation velocity to the local velocity dispersion of v/sigma=7.0 (v=386 km/s) and v/sigma_0=4.1 (v=391 km/s). Given that the descendants of these massive galaxies in the local universe are likely ellipticals with v/sigma nearly an order of magnitude lower, the rapidly rotating galaxies would lose significant net angular momentum in the intervening time. The comparisons among dynamical, stellar, gas, and dust mass suggest that the starburst CO-to-H2 conversion factor of alpha_CO=0.8 Msun/(K km/s/pc2) is appropriate in the spatially resolved cores. The dense cores are likely to be formed in extreme environments similar to the central regions of local ultraluminous infrared galaxies. Our work also demonstrates that a combination of medium-resolution CO and high-resolution dust continuum observations is a powerful tool for characterizing the dynamical state of molecular gas in distant galaxies., Comment: 6 pages, 4 figures, 1 table, accepted for publication in ApJ Letters

The Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) is a three-layered imaging survey aimed at addressing some of the most outstanding questions in astronomy today, including the nature of dark matter and dark energy. The survey has been awarded 300 nights of observing time at the Subaru Telescope and it started in March 2014. This paper presents the first public data release of HSC-SSP. This release includes data taken in the first 1.7 years of observations (61.5 nights) and each of the Wide, Deep, and UltraDeep layers covers about 108, 26, and 4 square degrees down to depths of i~26.4, ~26.5, and ~27.0 mag, respectively (5sigma for point sources). All the layers are observed in five broad bands (grizy), and the Deep and UltraDeep layers are observed in narrow bands as well. We achieve an impressive image quality of 0.6 arcsec in the i-band in the Wide layer. We show that we achieve 1-2 per cent PSF photometry (rms) both internally and externally (against Pan-STARRS1), and ~10 mas and 40 mas internal and external astrometric accuracy, respectively. Both the calibrated images and catalogs are made available to the community through dedicated user interfaces and database servers. In addition to the pipeline products, we also provide value-added products such as photometric redshifts and a collection of public spectroscopic redshifts. Detailed descriptions of all the data can be found online. The data release website is https://hsc-release.mtk.nao.ac.jp/., Comment: 34 pages, 20 figures, 7 tables, moderate revision, accepted for publication in PASJ

We have carried out a panoramic Ly$\alpha$ narrowband imaging with Suprime-Cam on Subaru towards the known protocluster USS1558--003 at $z=2.53$. Our previous narrowband imaging at near-infrared has identified multiple dense groups of H$\alpha$ emitters (HAEs) within the protocluster. We have now identified the large-scale structures across a $\sim$50 comoving Mpc scale traced by Ly$\alpha$ 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 Ly$\alpha$ photons than those of HAEs in lower-density regions. These phenomena may be driven by the extra depletion of Ly$\alpha$ emission lines along our line of sight by more intervening cold circumgalactic/intergalactic medium and/or dust existing in the dense core. We also caution that all the past high-$z$ protocluster surveys using LAEs as the tracers would have largely missed galaxies in the very dense cores of the protoclusters where we would expect to see any early environmental effects., Comment: 6 pages, 4 figures, accepted for publication in MNRAS Letter

We present 0".2-resolution Atacama Large Millimeter/submillimeter Array observations at 870 um for 25 Halpha-seleced star-forming galaxies (SFGs) around the main-sequence at z=2.2-2.5. We detect significant 870 um continuum emission in 16 (64%) of these SFGs. The high-resolution maps reveal that the dust emission is mostly radiated from a single region close to the galaxy center. Exploiting the visibility data taken over a wide $uv$ distance range, we measure the half-light radii of the rest-frame far-infrared emission for the best sample of 12 massive galaxies with logM*>11. We find nine galaxies to be associated with extremely compact dust emission with R_{1/2,870um}<1.5 kpc, which is more than a factor of 2 smaller than their rest-optical sizes, R_{1/2,1.6um}=3.2 kpc, and is comparable with optical sizes of massive quiescent galaxies at similar redshifts. As they have an exponential disk with Sersic index of n=1.2 in the rest-optical, they are likely to be in the transition phase from extended disks to compact spheroids. Given their high star formation rate surface densities within the central 1 kpc of Sigma SFR1kpc=40 Msol/yr/kpc^2, the intense circumnuclear starbursts can rapidly build up a central bulge with Sigma M*1kpc>1e10 Msol/kpc^2 in several hundred Myr, i.e. by z~2. Moreover, ionized gas kinematics reveal that they are rotation-supported with an angular momentum as large as that of typical SFGs at z=1-3. Our results suggest bulges are commonly formed in extended rotating disks by internal processes, not involving major mergers., Comment: 11 pages, 6 figures, 2 tables, accepted for publication in ApJ

We conducted a deep narrow-band imaging survey with the Subaru Prime Focus Camera on the Subaru Telescope and constructed a sample of Ly$\alpha$ emitters (LAEs) at z=2.53 in the UDS-CANDELS field where a sample of H$\alpha$ emitters (HAEs) at the same redshift is already obtained from our previous narrow-band observation at NIR. The deep narrow-band and multi broadband data allow us to find LAEs of stellar masses and star-formation rates (SFRs) down to $\gtrsim$$10^8$ M$_\odot$ and $\gtrsim$0.2 M$_\odot$/yr, respectively. We show that the LAEs are located along the same mass-SFR sequence traced by normal star-forming galaxies such as HAEs, but towards a significantly lower mass regime. Likewise, LAEs seem to share the same mass--size relation with typical star-forming galaxies, except for the massive LAEs, which tend to show significantly compact sizes. We identify a vigorous mass growth in the central part of LAEs: the stellar mass density in the central region of LAEs increases as their total galaxy mass grows. On the other hand, we see no Ly$\alpha$ line in emission for most of the HAEs. Rather, we find that the Ly$\alpha$ feature is either absent or in absorption (Ly$\alpha$ absorbers; LAAs), and its absorption strength may increase with reddening of the UV continuum slope. We demonstrate that a deep Ly$\alpha$ narrow-band imaging like this study is able to search for not only LAEs but also LAAs in a certain redshift slice. This work suggests that LAEs trace normal star-forming galaxies in the low-mass regime, while they remain as a unique population because the majority of HAEs are not LAEs., Comment: 20 pages, 18 figures, 3 tables, accepted for publication in MNRAS

We investigate a correlation between star-formation rate (SFR) and stellar mass for Halpha emission line galaxies (HAEs) in one of the richest proto-clusters ever known at z~2.5, USS 1558-003 proto-cluster. This study is based on a 9.7-hour narrow-band imaging data with MOIRCS on the Subaru telescope. We are able to construct a sample, in combination with additional H-band data taken with WFC3 on Hubble Space Telescope (HST), of 100 HAEs reaching the dust-corrected SFRs down to 3 Msun/yr and the stellar masses down to $10^{8.0}$ Msun. We find that while the star-forming galaxies with >$10^{9.3}$ Msun are located on the universal SFR-mass main sequence irrespective of the environment, less massive star-forming galaxies with <$10^{9.3}$ Msun show a significant upward scatter from the main sequence in this proto-cluster. This suggests that some less massive galaxies are in a starburst phase, although we do not know yet if this is due to environmental effects., Comment: 5 pages, 3 figures, 1 table, accepted for publication in the ApJ Letters