Search

We present the properties of Ly$\alpha$emitters (LAEs) at $z=5.7$in the Subaru Deep Field. A photometric sample of 89 LAE candidates was constructed from narrow-band data down to $\mathit{NB816} = 26.0$(AB) in a continuous $725 \,\mathrm{arcmin}^2$area. Spectra of 39 objects satisfying the photometric selection criteria for LAEs were obtained with Subaru and Keck II Telescopes, among which 28 were confirmed LAEs, one was a nearby galaxy, and eight were unclassified. We also obtained spectra of another 24 NB816-excess objects in the field, identifying six additional LAEs. We find that the Ly$\alpha$luminosity function derived from the photometric sample is reproduced well by a Schechter function with $L^\star = 7.9^{+3.0}_{-2.2} \times 10^{42} \,\mathrm{erg} \,\mathrm{s}^{-1}$and $\phi^\star = 6.3^{+3.0}_{-2.0} \times 10^{-4} \,\mathrm{Mpc}^{-3}$for $\alpha =-1.5$(fixed) over the whole luminosity range of $L \simeq 3 \times 10^{42} \hbox{--} 3 \times 10^{43} \,\mathrm{erg} \,\mathrm{s}^{-1}$. We then measured the rest-frame Ly$\alpha$equivalent widths for the confirmed LAEs, to find that the median among the 28 objects satisfying the photometric selection criteria is $W_{0}^{\mathrm{i}} = 233 \,{Å}$. We infer that 30%-40% of LAEs at $z=5.7$exceed $W_{0}^{\mathrm{i}} = 240 \,{Å}$. These large-EW objects probably cannot be accounted for by ordinary star-forming populations with a Salpeter IMF. We also find that LAEs with fainter far-UV luminosities have larger EWs. Finally, we derived the far-UV luminosity function of LAEs down to $M_{\mathrm{UV}} \simeq-19.6$using the photometric sample, and compared it with that of Lyman-break galaxies (LBGs). We find that as high as about 80% of LBGs at $z \sim 6$have $W_{0}^{\mathrm{i}} \ge 100 \,{Å}$, in sharp contrast to lower-$z$counterparts.

We present our ALMA Band 8 observations of a damped Ly$\alpha$absorption (DLA) system at $z = 3.150$observed in the spectrum of the quasar Q2233+131 at $z = 3.295$. The optical counterpart of this DLA has been identified and it shows a double-peaked Ly$\alpha$emission line. Since one possible origin of DLAs at high redshift is an outflowing gas from star-forming galaxies, DLA 2233+131 provides a good laboratory to investigate the nature of high-zDLAs. Motivated by this, we have carried out ALMA band 8 observations to study the [C ii] line in this system. However, we do not detect any significant emission line in the observed pass bands. Instead, we have serendipitously found three submm continuum sources in the observed sky area. One appears to be the quasar Q2233+131 itself while the other two sources are newly identified submm galaxies (SMGs), called SMG1 and SMG2 in this paper. They are located at a separation of ${4{^{\prime \prime }_{.}}7}$and ${8{^{\prime \prime }_{.}}1}$from Q2233+131, respectively. Their 646 μm fluxes are $6.35\:$mJy and $6.43\:$mJy, respectively, being higher than that of Q2233+131, $3.62\:$mJy. Since these two SMGs are not detected in the optical images obtained with the Hubble Space Telescope and the Subaru Telescope, they have a very red spectral energy distribution. It is, therefore, suggested that they are high-redshift galaxies or very dusty galaxies at intermediate redshift, although we cannot rule out the possibility that they are optically very faint SMG analogs at low redshift. Follow-up observations will be necessary to explore the nature of this interesting region.

We report on the results of deep and wide-field (1.1 deg2) narrow-band observations with Subaru/Hyper Suprime-Cam (HSC) of a field around a hyperluminous QSO (HLQSO), HS$\, 1549+$1919, residing in a protocluster at z= 2.84, to map the large-scale structure of Lyα emitters (LAEs). One HSC pointing enables us to detect 3490 LAEs and 76 extended Lyα blobs (LABs), probing diverse environments from voids to protoclusters. The HLQSO is found to be near the center of the protocluster, which corresponds to the intersection of $\sim \,$100 comoving Mpc-scale structures of LAEs. LABs are basically distributed along the large-scale structure, with larger ones particularly clustering around the HLQSO, confirming a previously noted tendency of LABs to prefer denser environments. Moreover, the shapes of LABs near the HLQSO appear to be aligned with the large-scale structure. Finally, a deep Lyα image reveals a diffuse Lyα nebula along a filamentary structure with no luminous UV/sub-mm counterpart. We suggest that the diffuse nebula is due to a cold filament with high clumping factor illuminated by the QSO, with the required high clumpiness provided by unresolved residing halos of mass $\le 10^{9-10}\, M_\odot$.

We present the results from ALMA CO(3–2) observations of 66 Hα-selected galaxies in three protoclusters around radio galaxies: PKS 1138−262 ($z$= 2.16), USS 1558−003 ($z$= 2.53), and 4C 23.56 ($z$= 2.49). The pointing areas have an overdensity of ∼100 compared to the mean surface number density of galaxies in field environments. We detect the CO emission line in 16 star-forming galaxies, including six previously published galaxies, to measure the molecular gas mass. In the stellar mass range of 10.5 < log (Mstar/M⊙) < 11.0, the protocluster galaxies have larger gas mass fractions and longer gas depletion timescales compared to the scaling relations established for field galaxies. On the other hand, the amounts of molecular gas in more massive galaxies with log (Mstar/M⊙) > 11.0 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.

We present the survey design, data reduction, construction of images, and source catalog of the Atacama Large Millimeter/submillimeter Array (ALMA) twenty-six arcmin2survey of GOODS-S at one millimeter (ASAGAO). ASAGAO is a deep (1 σ depth ∼ 61 μJy beam−1for a 250 kλ-tapered map with a synthesized beam size of 0${^{\prime\prime}_{.}}$51 × 0${^{\prime\prime}_{.}}$45) and wide area (26 arcmin2) survey on a contiguous field at 1.2 mm. By combining with ALMA archival data in the GOODS-South field, we obtained a deeper map in the same region (1 σ depth ∼ 30 μJy beam−1for a deep region with a 250 kλ-taper, and a synthesized beam size of 0${^{\prime\prime}_{.}}$59 × 0${^{\prime\prime}_{.}}$53), providing the largest sample of sources (25 sources at ≥5.0 σ, 45 sources at ≥4.5 σ) among ALMA blank-field surveys to date. The number counts show that $52^{+11}_{-8}$% of the extragalactic background light at 1.2 mm is resolved into discrete sources at S1.2 mm> 135 μJy. We create infrared (IR) luminosity functions (LFs) in the redshift range of $z$= 1–3 from the ASAGAO sources with Ks-band counterparts, and constrain the faintest luminosity of the LF at 2.0 < $z$< 3.0. The LFs are consistent with previous results based on other ALMA and SCUBA-2 observations, which suggest a positive luminosity evolution and negative density evolution with increasing redshift. We find that obscured star-formation of sources with IR luminosities of log (LIR/L⊙) ≳ 11.8 account for ≈60%–90% of the $z$∼ 2 cosmic star-formation rate density.

We present CO J= 4–3 line and 3 mm dust continuum observations of a 100 kpc-scale filamentary Lyα nebula (SSA22 LAB18) at z= 3.1 using the Atacama Large Millimeter/submillimeter Array (ALMA). We detected the CO J= 4–3 line at a systemic zCO= 3.093 ± 0.001 at 11 σ from one of the ALMA continuum sources associated with the Lyα filament. We estimated the CO J= 4–3 luminosity of $L^{\prime }_{\rm {CO(4-3)}}=(2.3 \pm 0.2)\times 10^{9}\:$K km s−1pc2for this CO source, which is one order of magnitude smaller than those of typical z> 1 dusty star-forming galaxies (DSFGs) of similar far-infrared luminosity LIR∼ 1012L⊙. We derived a molecular gas mass of $M_{\rm {gas}} = (4.4^{+0.9}_{-0.6}) \times 10^{9}\, M_{{\odot }}$and a star-formation rate of SFR =270 ± 160 M⊙yr−1. We also estimated a gas depletion time of τdep= 17 ± 10 Myr, which is shorter than those of typical DSFGs. It is suggested that this source is in the transition phase from DSFG to a gas-poor, early-type galaxy. From ALMA to Herschel multi-band dust continuum observations, we measured a dust emissivity index β = 2.3 ± 0.2, which is similar to those of local gas-poor, early-type galaxies. From recent laboratory experiments, the specific chemical compositions needed to reproduce such a high β for interstellar dust at the submillimeter wavelengths. ALMA CO and multi-band dust continuum observations can constrain the evolutionary stage of high-redshift galaxies through τdepand β, and thus we can investigate the chemical composition of dust even in the early Universe.

To search for dust-obscured star-formation activity in the early Universe, it is essential to obtain a deep and wide submillimeter/millimeter map. The advent of the Atacama Large Millimeter/submillimeter Array (ALMA) has enabled us to obtain such maps with sufficiently high spatial resolution to be free from source confusion. We present a new 1.1 mm-wave map obtained by ALMA in the SSA22 field. The field contains a remarkable proto-cluster at z= 3.09; therefore, it is an ideal region to investigate the role of a large-scale cosmic web on dust-obscured star formation. The typical 1σ depth of our map is 73 μJy beam−1with a ${0^{^{\prime\prime}_{.}}5}$resolution. Combining the present survey with earlier, archived observations, we map an area of 20 arcmin2(71 comoving Mpc2at z= 3.09). Within the combined survey area we have detected 35 sources at a signal-to-noise ratio (S/N) >5, with flux densities of S1.1mm= 0.43–5.6 mJy, equivalent to star-formation rates of ≳100–1000 M⊙yr−1at z= 3.09, for a Chabrier initial mass function: 17 sources out of 35 are new detections. The cumulative number counts show an excess by a factor of three to five compared to blank fields. The excess suggests enhanced, dust-enshrouded star-formation activity in the proto-cluster on a 10 comoving Mpc scale, indicating accelerated galaxy evolution in this overdense region.

We conduct a systematic search for galaxy protoclusters at z∼ 3.8 based on the latest internal data release (S16A) of the Hyper Suprime-Cam Subaru strategic program (HSC-SSP). In the Wide layer of the HSC-SSP, we investigate the large-scale projected sky distribution of g-dropout galaxies over an area of 121 deg2, and identify 216 large-scale overdense regions (>4 σ overdensity significance) that are likely protocluster candidates. Of these, 37 are located within 8΄ (3.4 physical Mpc) of other protocluster candidates of higher overdensity, and are expected to merge into a single massive structure by z= 0. Therefore, we find 179 unique protocluster candidates in our survey. A cosmological simulation that includes projection effects predicts that more than 76% of these candidates will evolve into galaxy clusters with halo masses of at least 1014M⊙by z= 0. The unprecedented size of our protocluster candidate catalog allows us to perform, for the first time, an angular clustering analysis of the systematic sample of protocluster candidates. We find a correlation length of 35.0 h−1Mpc. The relation between correlation length and number density of z∼ 3.8 protocluster candidates is consistent with the prediction of the ΛCDM model, and the correlation length is similar to that of rich clusters in the local universe. This result suggests that our protocluster candidates are tracing similar spatial structures to those expected from the progenitors of rich clusters, and enhances the confidence that our method for identifying protoclusters at high redshifts is robust. In years to come, our protocluster search will be extended to the entire HSC-SSP Wide sky coverage of ∼ 1400 deg2to probe cluster formation over a wide redshift range of z∼ 2–6.

We present the SILVERRUSH program strategy and clustering properties investigated with ∼2000 Lyα emitters (LAEs) at z= 5.7 and 6.6 found in the early data of the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey exploiting the carefully designed narrow-band filters. We derive angular correlation functions with the unprecedentedly large samples of LAEs at z= 6–7 over the large total area of 14–21 deg2corresponding to 0.3–0.5 comoving Gpc2. We obtain the average large-scale bias values of bavg= 4.1 ± 0.2 (4.5 ± 0.6) at z= 5.7 (z= 6.6) for ≳ L* LAEs, indicating a weak evolution of LAE clustering from z= 5.7 to 6.6. We compare the LAE clustering results with two independent theoretical models that suggest an increase of an LAE clustering signal by the patchy ionized bubbles at the epoch of reionization (EoR), and estimate the neutral hydrogen fraction to be $x_{\rm H\,{\small I}}=0.15^{+0.15}_{-0.15}$at z= 6.6. Based on the halo occupation distribution models, we find that the ≳ L* LAEs are hosted by dark-matter halos with an average mass of $\log (\left\langle M_{\rm h} \right\rangle /M_\odot ) =11.1^{+0.2}_{-0.4}$($10.8^{+0.3}_{-0.5}$) at z= 5.7 (6.6) with a Lyα duty cycle of 1% or less, where the results of z= 6.6 LAEs may be slightly biased, due to the increase of the clustering signal at the EoR. Our clustering analysis reveals the low-mass nature of ≳ L* LAEs at z= 6–7, and that these LAEs probably evolve into massive super-L* galaxies in the present-day universe.

We present spatially resolved properties of molecular gas and dust in a gravitationally lensed submillimeter galaxy H-ATLAS J090311.6+003906 (SDP.81) at z= 3.042 revealed by the Atacama Large Millimeter/submillimeter Array (ALMA). We identified 14 molecular clumps in the CO(5–4) line data. The surface density of molecular gas ($\Sigma _{\rm H_2}$) and star-formation rate (ΣSFR) of the clumps are more than three orders of magnitude higher than those found in local spiral galaxies. The clumps are placed in the “burst” sequence in the $\Sigma _{\rm H_2}$–ΣSFRplane, suggesting that z∼ 3 molecular clumps follow the star-formation law derived for local starburst galaxies. With our gravitational lens model, the positions in the source plane are derived for the molecular clumps, dust clumps, and stellar components identified in the Hubble Space Telescope image. The molecular and dust clumps are confined within a ∼ 2 kpc region, while the spatial extent of the stellar components is as large as ∼ 6 kpc and offset toward the west. The molecular clumps have a systematic velocity gradient in the north–south direction, which may indicate a rotating gas disk. One possible scenario is that the components of molecular gas, dust, and stars are distributed in a several-kpc-scale rotating disk, and the stellar emission is heavily obscured by dust in the central star-forming region. Alternatively, SDP.81 can be explained by a merging system, where dusty starbursts occur in the region where the two galaxies collide, surrounded by tidal features traced in the stellar components.

We present the results of deep near-infrared imaging observations of the $z=3.1$ proto-cluster region in the SSA?22a field taken by MOIRCS mounted on the Subaru Telescope. We observed a 21.7?arcmin$^2$ field to depths of $J=$ 24.5, $H=$ 24.3, and $K=$ 23.9 (5$\sigma$). We examined the distribution of the $K$-selected galaxies at $z \sim 3$ by using a simple color cut for distant red galaxies (DRGs) as well as a photometric-redshift selection technique. The marginal density excess of DRGs and the photo-$z$ selected objects were found around the two most luminous Ly$\alpha$ blobs (LABs). We investigated the correlation between the $K$-selected objects and the LABs, and found that several galaxies with stellar mass, $M_* = 10^{9}$–$10^{11} M_\odot$, exist in the vicinity of LABs, especially around the two most luminous ones. We also found that 7 of the 8LABs in the field have plausible $K_{\rm s}$-band counterparts, and the sum of the stellar mass possibly associated with LABs correlates with their luminosity and surface brightness, which implies that the origin of Ly$\alpha$ emission may be closely correlated with their previous star-formation phenomena.