arXiv subjects

Kazuhiro Shimasaku

Publications and source records attributed to Kazuhiro Shimasaku.

At least 55 records · Page 3Linked to original sources

arXiv2020

Statistical correlation between the distribution of Ly$α$ emitters and IGM HI at $z\sim2.2$ mapped by Subaru/Hyper Suprime-Cam

The correlation between neutral Hydrogen (HI) in the intergalactic medium (IGM) and galaxies now attracts great interests. We select four fields which include several coherently strong Ly$α$ absorption systems at $z\sim2.2$ detected by using background quasars from the whole SDSS/(e)BOSS database. Deep narrow-band and $g$-band imaging are performed using the Hyper Suprime-Cam on the Subaru Telescope. We select out 2,642 Ly$α$ emitter (LAE) candidates at $z=2.177\pm0.023$ down to the Ly$α$ luminosity of $L_{\text{Ly}α}\approx 2 \times 10^{42} {\rm erg~s}^{-1}$ to construct the galaxy overdensity maps, covering an effective area of 5.39 deg$^2$. Combining the sample with the Ly$α$ absorption estimated from 64 (e)BOSS quasar spectra, we find a moderate to strong correlation between the LAE overdensity $δ_{\rm LAE}$ and the effective optical depth $τ_{\rm LoS}$ in line-of-sights, with $P$-value$=0.09\%$ ($<0.01\%$) when the field that contains a significant quasar overdensity is in(ex)cluded. The cross-correlation analysis also clearly suggests that up to $4\pm1$ pMpc, LAEs tend to cluster in the regions rich in HI gas, indicated by the high $τ_{\rm LoS}$, and avoid the low $τ_{\rm LoS}$ region where the HI gas is deficient. By averaging the $τ_{\rm LoS}$ as a function of the projected distance ($d$) to LAEs, we find a $30\%$ excess signal at $2σ$ level at $d<200$ pkpc, indicating the dense HI in circumgalactic medium, and a tentative excess at $400<d<600$ pkpc in IGM regime, corroborating the cross-correlation signal detected at about $0.5$ pMpc. These statistical analyses indicate that galaxy$-$IGM HI correlations exist on scales ranging from several hundred pkpc to several pMpc at $z\sim2.2$.

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arXiv2020

Dual supermassive black holes at close separation revealed by the Hyper Suprime-Cam Subaru Strategic Program

The unique combination of superb spatial resolution, wide-area coverage, and deep depth of the optical imaging from the Hyper Suprime-Cam (HSC) Subaru Strategic Program is utilized to search for dual quasar candidates. Using an automated image analysis routine on 34,476 known SDSS quasars, we identify those with two (or more) distinct optical point sources in HSC images covering 796 deg^2. We find 421 candidates out to a redshift of 4.5 of which one hundred or so are more likely after filtering out contaminating stars. Angular separations of 0.6 - 4.0" correspond to projected separations of 3 - 30 kpc, a range relatively unexplored for population studies of luminous dual quasars. Using Keck-I/LRIS and Gemini-N/NIFS, we spectroscopically confirm three dual quasar systems at z < 1, two of which are previously unknown out of eight observed, based on the presence of characteristic broad emission lines in each component, while highlighting that the continuum of one object in one of the pairs is reddened. In all cases, the [OIII]5007 emission lines have mild velocity offsets, thus the joint [OIII] line profile is not double-peaked. We find a dual quasar fraction of 0.26+/-0.18% and no evidence for evolution. A comparison with the Horizon-AGN simulation seems to support the case of no evolution in the dual quasar fraction when broadly matching the quasar selection. These results may indicate a scenario in which the frequency of the simultaneous triggering of luminous quasars is not as sensitive as expected to the cosmic evolution of the merger rate or gas content of galaxies.

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arXiv2020

A Systematic Search for Galaxy Proto-Cluster Cores at $z\sim 2$

A proto-cluster core is the most massive dark matter halo (DMH) in a given proto-cluster. To reveal the galaxy formation in core regions, we search for proto-cluster cores at $z\sim 2$ in $\sim 1.5\, \mathrm{deg}^{2}$ of the COSMOS field. Using pairs of massive galaxies ($\log(M_{*}/M_{\odot})\geq11$) as tracers of cores, we find 75 candidate cores, among which 54\% are estimated to be real. A clustering analysis finds that these cores have an average DMH mass of $2.6_{-0.8}^{+0.9}\times 10^{13}\, M_{\odot}$, or $4.0_{-1.5}^{+1.8}\, \times 10^{13} M_{\odot}$ after contamination correction. The extended Press-Schechter model shows that their descendant mass at $z=0$ is consistent with Fornax-like or Virgo-like clusters. Moreover, using the IllustrisTNG simulation, we confirm that pairs of massive galaxies are good tracers of DMHs massive enough to be regarded as proto-cluster cores. We then derive the stellar mass function (SMF) and the quiescent fraction for member galaxies of the 75 candidate cores. We find that the core galaxies have a more top-heavy SMF than field galaxies at the same redshift, showing an excess at $\log(M_{*}/M_{\odot})\gtrsim 10.5$. The quiescent fraction, $0.17_{-0.04}^{+0.04}$ in the mass range $9.0\leq \log(M_{*}/M_{\odot})\leq 11.0$, is about three times higher than that of field counterparts, giving an environmental quenching efficiency of $0.13_{-0.04}^{+0.04}$. These results suggest that stellar mass assembly and quenching are accelerated as early as at $z\sim 2$ in proto-cluster cores.

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arXiv2020

Implications of the mild gas motion found with Hitomi in the core of the Perseus cluster

Based mainly on X-ray observations, studies are made on interactions between the intra-cluster medium (ICM) in clusters of galaxies and their member galaxies. Through (magneto)hydrodynamic and gravitational channels, the moving galaxies are expected to drag the ICM around them, and transfer to the ICM some fraction of their dynamical energies on cosmological time scales. This hypothesis is in line with several observations, including the possible cosmological infall of galaxies towards the cluster center, found over redshifts of z~1 to z~0. Further assuming that the energy lost by the galaxies is first converted into ICM turbulence and then dissipated, this picture can explain the subsonic and uniform ICM turbulence, measured with Hitomi in the core region of the Perseus cluster. The scenario may also explain several other unanswered problems regarding clusters of galaxies, including what prevents the ICM from the expected radiative cooling, how the various mass components in nearby clusters have attained different radial distributions, and how a thermal stability is realized between hot and cool ICM components that co-exist around cD galaxies. This view is also considered to pertain to the general scenario of galaxy evolution, including their environmental effects.

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arXiv2020

Possible evolution of the circum-galactic medium around QSOs with QSO age and cosmic time revealed by Ly$α$ halos

We first present new Subaru narrow-band observations of the Ly$α$ halo around the quasi-stellar object (QSO) CFHQ J232908$-$030158 at $z=6.42$, which appears the most luminous and extended halo at $z>5$ ($L_{Lyα}=9.8\times10^{43}$ erg s$^{-1}$ within $37$ pkpc diameter). Then, combining these measurements with available data in the literature, we find two different evolutions of QSOs' Ly$α$ halos. First is a possible short-term evolution with QSO age seen in four $z>6$ QSOs. We find the anti-correlation between the Ly$α$ halo scales with QSOs' IR luminosity, with J2329-0301's halo being the brightest and largest. It indicates that ionizing photons escape more easily out to circum-galactic regions when host galaxies are less dusty. We also find a positive correlation between IR luminosity and black hole mass ($M_\text{BH}$). Given $M_\text{BH}$ as an indicator of QSO age, we propose a hypothesis that a large Ly$α$ halo mainly exists around QSOs in the young phase of their activity due to a small amount of dust. The second is an evolution with cosmic time seen over $z\sim2-5$. We find the increase of surface brightness toward lower-redshift with a similar growth rate to that of dark matter halos (DHs) which evolve to $M_\text{DH}=10^{12}-10^{13}$ M$_\odot$ at $z=2$. The extent of Ly$α$ halos is also found to increase at a rate scaling with the virial radius of growing DHs, $r_\text{vir} \propto M_\text{DH}^{1/3}$($1+z$)$^{-1}$. These increases are consistent with a scenario that the CGM around QSOs evolves in mass and size keeping pace with hosting DHs.

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arXiv2019

The CFHT Large Area U-band Deep Survey (CLAUDS)

The CFHT Large Area U-band Deep Survey (CLAUDS) uses data taken with the MegaCam mosaic imager on CFHT to produce images of 18.60 deg2 with median seeing of FWHM=0.92 arcsec and to a median depth of U = 27.1 AB (5 sigma in 2 arcsec apertures), with selected areas that total 1.36 deg2 reaching a median depth of U=27.7 AB. These are the deepest U-band images assembled to date over this large an area. These data are located in four fields also imaged to comparably faint levels in grizy and several narrowband filters as part of the Hyper Suprime-Cam (HSC) Subaru Strategic Program (HSC-SSP). These CFHT and Subaru datasets will remain unmatched in their combination of area and depth until the advent of the Large Synoptic Survey Telescope (LSST). This paper provides an overview of the scientific motivation for CLAUDS and gives details of the observing strategy, observations, data reduction, and data merging with the HSC-SSP. Three early applications of these deep data are used to illustrate the potential of the dataset: deep U-band galaxy number counts, z~3 Lyman break galaxy (LBG) selection, and photometric redshifts improved by adding CLAUDS U to the Subaru HSC grizy photometry.

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arXiv2019

CHORUS. III. Photometric and Spectroscopic Properties of Ly$α$ Blobs at $z=4.9-7.0$

We report the Subaru Hyper Suprime-Cam (HSC) discovery of two Ly$α$ blobs (LABs), dubbed z70-1 and z49-1 at $z=6.965$ and $z=4.888$ respectively, that are Ly$α$ emitters with a bright ($\log L_{\rm Lyα}/{\rm [erg\ s^{-1}]}>43.4$) and spatially-extended Ly$α$ emission, and present the photometric and spectroscopic properties of a total of seven LABs; the two new LABs and five previously-known LABs at $z=5.7-6.6$. The z70-1 LAB shows the extended Ly$α$ emission with a scale length of $1.4\pm 0.2$ kpc, about three times larger than the UV continuum emission, making z70-1 the most distant LAB identified to date. All of the 7 LABs, except z49-1, exhibit no AGN signatures such as X-ray emission, {\sc Nv}$λ$1240 emission, or Ly$α$ line broadening, while z49-1 has a strong {\sc Civ}$λ$1548 emission line indicating an AGN on the basis of the UV-line ratio diagnostics. We carefully model the point-spread functions of the HSC images, and conduct two-component exponential profile fitting to the extended Ly$α$ emission of the LABs. The Ly$α$ scale lengths of the core (star-forming region) and the halo components are $r_{\rm c}=0.6-1.2$ kpc and $r_{\rm h}=2.0-13.8$ kpc, respectively. The average $r_{\rm h}$ of the LABs falls on the extrapolation of the $r_{\rm h}$-Ly$α$ luminosity relation of the Ly$α$ halos around VLT/MUSE star-forming galaxies at the similar redshifts, suggesting that typical LABs at $z\gtrsim5$ are not special objects, but star-forming galaxies at the bright end.

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arXiv2019

The dominant origin of diffuse Ly$α$ halos around LAEs explored by SED fitting and clustering analysis

The physical origin of diffuse Ly$α$ halos (LAHs) around star-forming galaxies is still a matter of debate. We present the dependence of LAH luminosity ($L({\rm Ly}α)_H$) on the stellar mass ($M_\star$), $SFR$, color excess ($E(B-V)_\star$), and dark matter halo mass ($M_{\rm h}$) of the parent galaxy for $\sim 900$ Ly$α$ emitters (LAEs) at $z\sim2$ divided into ten subsamples. We calculate $L({\rm Ly}α)_H$ using the stacked observational relation between $L({\rm Ly}α)_H$ and central Ly$α$ luminosity by Momose et al. (2016), which we find agrees with the average trend of VLT/MUSE-detected individual LAEs. We find that our LAEs have relatively high $L({\rm Ly}α)_H$ despite low $M_\star$ and $M_{\rm h}$, and that $L({\rm Ly}α)_H$ remains almost unchanged with $M_\star$ and perhaps with $M_{\rm h}$. These results are incompatible with the cold stream (cooling radiation) scenario and the satellite-galaxy star-formation scenario, because the former predicts fainter $L({\rm Ly}α)_H$ and both predict steeper $L({\rm Ly}α)_H$ vs. $M_\star$ slopes. We argue that LAHs are mainly caused by Ly$α$ photons escaping from the main body and then scattered in the circum-galactic medium. This argument is supported by LAH observations of H$α$ emitters (HAEs). When LAHs are taken into account, the Ly$α$ escape fractions of our LAEs are about ten times higher than those of HAEs with similar $M_\star$ or $E(B-V)_\star$, which may partly arise from lower HI gas masses implied from lower $M_{\rm h}$ at fixed $M_\star$, or from another Ly$α$ source in the central part.

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arXiv2019

Black versus Dark: Rapid Growth of Supermassive Black Holes in Dark Matter Halos at z ~ 6

We report on the relation between the mass of supermassive black holes (SMBHs; M_BH) and that of hosting dark matter halos (M_h) for 49 z ~ 6 quasi-stellar objects (QSOs) with [CII]158um velocity-width measurements. Here, we estimate M_h assuming that the rotation velocity from FWHM_CII is equal to the circular velocity of the halo; we have tested this procedure using z ~ 3 QSOs that also have clustering-based M_h estimates. We find that a vast majority of the z ~ 6 SMBHs are more massive than expected from the local M_BH - M_h relation, with one-third of the sample by factors >~ 10^2. The median mass ratio of the sample, M_BH/M_h = 6 x 10^{-4}, means that 0.4% of the baryons in halos are locked up in SMBHs. The mass growth rates of our SMBHs amount to ~ 10% of the SFRs, or ~ 1% of the mean baryon accretion rates, of the hosting galaxies. A large fraction of the hosting galaxies are consistent with average galaxies in terms of SFR and perhaps of stellar mass and size. Our study indicates that the growth of SMBHs (M_BH ~ 10^{8-10} Msun) in luminous z ~ 6 QSOs greatly precedes that of hosting halos owing to efficient gas accretion even under normal star formation activities, although we cannot rule out the possibility that undetected SMBHs have local M_BH/M_h ratios. This preceding growth is in contrast to much milder evolution of the stellar-to-halo mass ratio.

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arXiv2018

CHORUS II. Subaru/HSC Determination of the Ly$α$ Luminosity Function at $z=7.0$: Constraints on Cosmic Reionization Model Parameter

We present the Ly$α$ luminosity function (LF) derived from 34 Ly$α$ emitters (LAEs) at $z=7.0$ on the sky of $3.1$ deg$^2$, the largest sample compared to those in the literature obtained at a redshift $z\gtrsim7$. The LAE sample is made by deep large-area Subaru narrowband observations conducted by the Cosmic HydrOgen Reionization Unveiled with Subaru (CHORUS) project. The $z=7.0$ Ly$α$ LF of our project is consistent with those of the previous DECam and Subaru studies at the bright and faint ends, respectively, while our $z=7.0$ Ly$α$ LF has uncertainties significantly smaller than those of the previous study results. Exploiting the small errors of our measurements, we investigate the shape of the faint to bright-end Ly$α$ LF. We find that the $z=7.0$ Ly$α$ LF shape can be explained by the steep slope of $α\simeq -2.5$ suggested at $z=6.6$, and that there is no clear signature of a bright-end excess at $z\simeq 7$ claimed by the previous work, which was thought to be made by the ionized bubbles around bright LAEs whose Ly$α$ photons could easily escape from the partly neutral IGM at $z \simeq 7$. We estimate the Ly$α$ luminosity densities (LDs) with Ly$α$ LFs at $z\simeq 6-8$ given by our and the previous studies, and compare the evolution of the UV-continuum LD estimated with dropouts. The Ly$α$ LD monotonically decreases from $z\sim 6$ to $8$, and evolves stronger than the UV-continuum LD, indicative of the Ly$α$ damping wing absorption of the IGM towards the heart of the reionization epoch.

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arXiv2018

SILVERRUSH. VI. A simulation of Ly$α$ emitters in the reionization epoch and a comparison with Subaru Hyper Suprime-Cam survey early data

The survey of Lyman $α$ emitters (LAEs) with Subaru Hyper Suprime-Cam, called SILVERRUSH (Ouchi et al.), is producing massive data of LAEs at $z\gtrsim6$. Here we present LAE simulations to compare the SILVERRUSH data. In 162$^3$ comoving Mpc$^3$ boxes, where numerical radiative transfer calculations of reionization were performed, LAEs have been modeled with physically motivated analytic recipes as a function of halo mass. We have examined $2^3$ models depending on the presence or absence of dispersion of halo Ly$α$ emissivity, dispersion of the halo Ly$α$ optical depth, $τ_α$, and halo mass dependence of $τ_α$. The unique free parameter in our model, a pivot value of $τ_α$, is calibrated so as to reproduce the $z=5.7$ Ly$α$ luminosity function (LF). We compare our model predictions with Ly$α$ LFs at $z=6.6$ and $7.3$, LAE angular auto-correlation functions (ACFs) at $z=5.7$ and $6.6$, and LAE fractions in Lyman break galaxies at $5<z<7$. The Ly$α$ LFs and ACFs are reproduced by multiple models, but the LAE fraction turns out to be the most critical test. The dispersion of $τ_α$ and the halo mass dependence of $τ_α$ are essential to explain all observations reasonably. Therefore, a simple model of one-to-one correspondence between halo mass and Ly$α$ luminosity with a constant Ly$α$ escape fraction has been ruled out. Based on our best model, we present a formula to estimate the intergalactic neutral hydrogen fraction, $x_{\rm HI}$, from the observed Ly$α$ luminosity density at $z\gtrsim6$. We finally obtain $x_{\rm HI}=0.5_{-0.3}^{+0.1}$ as a volume-average at $z=7.3$.

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arXiv2018

Size--luminosity relations and UV luminosity functions at $z=6-9$ simultaneously derived from the complete Hubble Frontier Fields data

We construct $z\sim6-7$, 8, and 9 faint Lyman break galaxy samples (334, 61, and 37 galaxies, respectively) with accurate size measurements with the software $\texttt{glafic}$ from the complete Hubble Frontier Fields (FF) cluster and parallel fields data. These are the largest samples hitherto and reach down to the faint ends of recently obtained deep luminosity functions. At faint magnitudes, however, these samples are highly incomplete for galaxies with large sizes, implying that derivation of the luminosity function (LF) sensitively depends on the intrinsic size--luminosity (RL) relation. We thus conduct simultaneous maximum-likelihood estimation of LF and RL relation parameters from the observed distribution of galaxies on the RL plane with help of a completeness map as a function of size and luminosity. At $z\sim6-7$, we find that the intrinsic RL relation expressed as $r_\textrm{e} \propto L^β$ has a notably steeper slope of $β=0.46^{+0.08}_{-0.09}$ than those at lower redshifts, which in turn implies that the LF has a relatively shallow faint-end slope of $α=-1.86^{+0.17}_{-0.18}$. This steep $β$ can be reproduced by a simple analytical model in which smaller galaxies have lower specific angular momenta. The $β$ and $α$ values for the $z\sim8$ and 9 samples are consistent with those for $z\sim6-7$ but with larger errors. For all three samples there is a large, positive covariance between $β$ and $α$, implying that the simultaneous determination of these two parameters is important. We also provide new strong lens mass models of Abell S1063 and Abell 370 as well as updated mass models of Abell 2744 and MACS J0416.1$-$2403.

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arXiv2018

Full-Data Results of Hubble Frontier Fields: UV Luminosity Functions at $z\sim6-10$ and a Consistent Picture of Cosmic Reionization

We present UV luminosity functions of dropout galaxies at $z\sim6-10$ with the complete Hubble Frontier Fields data. We obtain a catalog of $\sim450$ dropout-galaxy candidates (350, 66, and 40 at $z\sim6-7$, 8, and 9, respectively), whose UV absolute magnitudes reach $\sim-14$ mag, $\sim2$ mag deeper than the Hubble Ultra Deep Field detection limits. We carefully evaluate number densities of the dropout galaxies by Monte-Carlo simulations, including all lensing effects such as magnification, distortion, and multiplication of images as well as detection completeness and contamination effects in a self-consistent manner. We find that UV luminosity functions at $z\sim6-8$ have steep faint-end slopes, $α\sim-2$, and likely steeper slopes, $α\lesssim-2$ at $z\sim9-10$. We also find that the evolution of UV luminosity densities shows a non-accelerated decline beyond $z\sim8$ in the case of $M_\mathrm{trunc}=-15$, while an accelerated in the case of $M_\mathrm{trunc}=-17$. We examine whether our results are consistent with the Thomson scattering optical depth from the Planck satellite and the ionized hydrogen fraction $Q_\mathrm{HII}$ at $z\lesssim7$ based on the standard analytic reionization model. We find that there exist reionizaiton scenarios that consistently explain all the observational measurements with the allowed parameters of $f_{\rm esc}=0.17^{+0.07}_{-0.03}$ and $M_\mathrm{trunc}>-14.0$ for $\logξ_\mathrm{ion}/[\mathrm{erg}^{-1}\ \mathrm{Hz}]=25.34$, where $f_{\rm esc}$ is the escape fraction, $M_\mathrm{trunc}$ is the faint limit of the UV luminosity function, and $ξ_\mathrm{ion}$ is the conversion factor of the UV luminosity to the ionizing photon emission rate. The length of the reionization period is estimated to be $Δz=3.9^{+2.0}_{-1.6}$ (for $0.1<Q_\mathrm{HII}<0.99$), consistent with the recent estimate from Planck.

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arXiv2017

The Stellar Mass, Star Formation Rate and Dark Matter Halo Properties of LAEs at $z\sim2$

We present average stellar population properties and dark matter halo masses of $z \sim 2$ \lya emitters (LAEs) from SED fitting and clustering analysis, respectively, using $\simeq$ $1250$ objects ($NB387\le25.5$) in four separate fields of $\simeq 1$ deg$^2$ in total. With an average stellar mass of $10.2\, \pm\, 1.8\times 10^8\ {\mathrm M_\odot}$ and star formation rate of $3.4\, \pm\, 0.4\ {\mathrm M_\odot}\ {\rm yr^{-1}}$, the LAEs lie on an extrapolation of the star-formation main sequence (MS) to low stellar mass. Their effective dark matter halo mass is estimated to be $4.0_{-2.9}^{+5.1} \times 10^{10}\ {\mathrm M_\odot}$ with an effective bias of $1.22^{+0.16}_{-0.18}$ which is lower than that of $z \sim 2$ LAEs ($1.8\, \pm\, 0.3$), obtained by a previous study based on a three times smaller survey area, with a probability of $96\%$. However, the difference in the bias values can be explained if cosmic variance is taken into account. If such a low halo mass implies a low HI gas mass, this result appears to be consistent with the observations of a high \lya escape fraction. With the low halo masses and ongoing star formation, our LAEs have a relatively high stellar-to-halo mass ratio (SHMR) and a high efficiency of converting baryons into stars. The extended Press-Schechter formalism predicts that at $z=0$ our LAEs are typically embedded in halos with masses similar to that of the Large Magellanic Cloud (LMC); they will also have similar SHMRs to the LMC, if their SFRs are largely suppressed after $z \sim 2$ as some previous studies have reported for the LMC itself.

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arXiv2017

Lyman-Break Galaxies at $z\sim 3$ in the Subaru Deep Field: Luminosity Function, Clustering and [OIII] Emission

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 $α=-1.78 \pm 0.05$. 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$β$ lines. Their implied equivalent widths increase with decreasing mass, reaching $\rm{EW_0([O III]4959,5007+Hβ)}$ =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.

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arXiv2017

SILVERRUSH. IV. Ly$α$ Luminosity Functions at $z = 5.7$ and $6.6$ Studied with $\sim$ 1,300 LAEs on the $14-21$ deg$^2$ Sky

We present the Ly$α$ luminosity functions (LFs) at $z=$5.7 and 6.6 derived from a new large sample of 1,266 Ly$α$ emitters (LAEs) identified in total areas of 14 and 21 deg$^2$, respectively, based on the early narrowband data of the Subaru/Hyper Suprime-Cam (HSC) survey. Together with careful Monte-Carlo simulations that account for the incompleteness of the LAE selection and the flux estimate systematics in the narrowband imaging, we have determined the Ly$α$ LFs with the unprecedentedly small statistical and systematic uncertainties in a wide Ly$α$ luminosity range of $10^{42.8-43.8}$ erg s$^{-1}$. We obtain the best-fit Schechter parameters of $L^{*}_{\rm Lya}=1.6^{+2.2}_{-0.6} (1.7^{+0.3}_{-0.7}) \times10^{43}$ erg s$^{-1}$, $ϕ^{*}_{\rm Lya}=0.85^{+1.87}_{-0.77}\ (0.47^{+1.44}_{-0.44})\times10^{-4}$ Mpc$^{-3}$, and $α=-2.6^{+0.6}_{-0.4}\ (-2.5^{+0.5}_{-0.5})$ at $z=5.7$ ($6.6$). We confirm that our best-estimate Ly$α$ LFs are consistent with the majority of the previous studies, but find that our Ly$α$ LFs do not agree with the high number densities of LAEs recently claimed by Matthee/Santos et al.'s studies that may overcorrect the incompleteness and the flux systematics. Our Ly$α$ LFs at $z=5.7$ and $6.6$ show an indication that the faint-end slope is very steep ($α\simeq -2.5$), although it is also possible that the bright-end LF results are enhanced by systematic effects such as the contribution from AGNs, blended merging galaxies, and/or large ionized bubbles around bright LAEs. Comparing our Ly$α$ LF measurements with four independent reionization models, we estimate the neutral hydrogen fraction of the IGM to be $x_{\rm HI}=0.3\pm0.2$ at $z=$6.6 that is consistent with the small Thomson scattering optical depth obtained by Planck 2016.

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arXiv2017

SILVERRUSH. II. First Catalogs and Properties of ~2,000 Lya Emitters and Blobs at z~6-7 Identified over the 14-21 deg2 Sky

We present an unprecedentedly large catalog consisting of 2,230 > L* Lya emitters (LAEs) at z=5.7 and 6.6 on the 13.8 and 21.2 deg2 sky, respectively, that are identified by the SILVERRUSH program with the first narrowband imaging data of the Hyper Suprime-Cam (HSC) survey. We confirm that the LAE catalog is reliable on the basis of 96 LAEs whose spectroscopic redshifts are already determined by this program and the previous studies. This catalogue is also available on-line. Based on this catalogue, we derive the rest-frame Lya equivalent-width distributions of LAEs at z~5.7-6.6 that are reasonably explained by the exponential profiles with the scale lengths of ~120-170A, showing no significant evolution from z~5.7 to z~6.6. We find that 275 LAEs with a large equivalent width (LEW) of >240A are candidates of young-metal poor galaxies and AGNs. We also find that the fraction of LEW LAEs to all ones is 4% and 21% at z~5.7 and z~6.6, respectively. Our LAE catalog includes 11 Lya blobs (LABs) that are LAEs with spatially extended Lya emission whose profile is clearly distinguished from those of stellar objects at the >~ 3sigma level. The number density of the LABs at z=6-7 is ~ 10^-7-10^-6 Mpc^-3, being ~ 10-100 times lower than those claimed for LABs at z~ 2-3, suggestive of disappearing LABs at z>~6, albeit with the different selection methods and criteria for the low and high-z LABs.

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arXiv2017

SILVERRUSH. III. Deep Optical and Near-Infrared Spectroscopy for Lya and UV-Nebular Lines of Bright Lya Emitters at z=6-7

We present Lya and UV-nebular emission line properties of bright Lya emitters (LAEs) at z=6-7 with a luminosity of log L_Lya/[erg s-1] = 43-44 identified in the 21-deg2 area of the SILVERRUSH early sample developed with the Subaru Hyper Suprime-Cam (HSC) survey data. Our optical spectroscopy newly confirm 21 bright LAEs with clear Lya emission, and contribute to make a spectroscopic sample of 96 LAEs at z=6-7 in SILVERRUSH. From the spectroscopic sample, we select 7 remarkable LAEs as bright as Himiko and CR7 objects, and perform deep Keck/MOSFIRE and Subaru/nuMOIRCS near-infrared spectroscopy reaching the 3sigma-flux limit of ~ 2x10^{-18} erg s-1 for the UV-nebular emission lines of He II1640, C IV1548,1550, and O III]1661,1666. Except for one tentative detection of C IV, we find no strong UV-nebular lines down to the flux limit, placing the upper limits of the rest-frame equivalent widths (EW_0) of ~2-4 A for He II, C IV, and O III] lines. Here we also investigate the VLT/X-SHOOTER spectrum of CR7 whose 6 sigma detection of He II is claimed by Sobral et al. Although two individuals and the ESO-archive service carefully re-analyze the X-SHOOTER data that are used in the study of Sobral et al., no He II signal of CR7 is detected, supportive of weak UV-nebular lines of the bright LAEs even for CR7. Spectral properties of these bright LAEs are thus clearly different from those of faint dropouts at z~7 that have strong UV-nebular lines shown in the various studies. Comparing these bright LAEs and the faint dropouts, we find anti-correlations between the UV-nebular line EW_0 and UV-continuum luminosity, which are similar to those found at z~2-3.

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