We report 14 and 26 protocluster candidates at z = 5.7 and 6.6 over 14 and 16 deg2 areas, respectively, selected from 2230 (259) Ly emitters (LAEs) photometrically (spectroscopically) identified ...using Subaru/Hyper Suprime-Cam (HSC) deep images (Keck, Subaru, and Magellan spectra, and literature data). Six out of the 40 protocluster candidates include one to 13 spectroscopically confirmed LAEs. We conduct Monte Carlo simulations to estimate how many protocluster candidates are found by chance for randomly distributed sources, and find that the effective number of protocluster candidates at z = 5.7 (6.6) is six (five). By comparing with the cosmological Ly radiative transfer (RT) model reproducing the LAEs with reionization effects, we find that more than half of these protocluster candidates are progenitors of present-day clusters with mass of . We then investigate the correlation between the LAE overdensity δ and the Ly rest-frame equivalent width , because the cosmological Ly RT model suggests that the slope of the -δ relation steepens toward the epoch of cosmic reionization (EoR), due to the existence of ionized bubbles around galaxy overdensities easing the escape of Ly emission from the partly neutral intergalactic medium. The available HSC data suggest that the slope of the -δ correlation does not evolve from the post-reionization epoch, z = 5.7, to the EoR, z = 6.6, beyond the moderately large statistical errors. There is a possibility that we could detect the evolution of the -δ relation from z = 5.7 to 7.3 using the upcoming HSC observations that will provide large samples of LAEs at z = 6.6-7.3.
Abstract
We present average stellar population properties and dark matter halo masses of z ∼ 2 Lyα emitters (LAEs) from spectral energy distribution fitting and clustering analysis, respectively, ...using ≃ 1250 objects ($\mathit {NB387}\le 25.5$) in four separate fields of ≃ 1 deg2 in total. With an average stellar mass of 10.2 ± 1.8 × 108 M⊙ and star formation rate of 3.4 ± 0.4 M⊙ 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 $4.0_{-2.9}^{+5.1} \times 10^{10}{\,\,}M_{\odot }$ with an effective bias of $1.22^{+0.16}_{-0.18}$, which is lower than that of z ∼ 2 LAEs (1.8 ± 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 H i gas mass, this result appears to be consistent with the observations of a high Lyα 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 star formation rates are largely suppressed after z ∼ 2 as some previous studies have reported for the LMC itself.
ABSTRACT
We present the Ly
α
luminosity functions (LFs) derived by our deep Subaru narrowband survey that identifies a total of 3137 Ly
α
emitters (LAEs) at
z
= 2.2 in five independent blank fields. ...This sample of LAEs is the largest to date and covers a very wide Ly
α
luminosity range of
erg s
−1
. We determine the Ly
α
LF at
z
= 2.2 with unprecedented accuracy and obtain the best-fit Schechter parameters of
erg s
−1
,
Mpc
−3
, and
, showing a steep faint-end slope. We identify a significant hump at the LF bright end (
erg s
−1
). Because all of the LAEs in the bright-end hump have a bright counterpart(s) in either the X-ray, UV, or radio data, this bright-end hump is not made by gravitational lensing magnification bias but by active galactic nuclei (AGNs). These AGNs allow us to derive the AGN UV LF at
z
∼ 2 down to the faint magnitude limit of
M
UV
≃ −22.5 and to constrain the faint-end slope of the AGN UV LF,
α
AGN
= −1.2 ± 0.1, which is flatter than those at
z
> 4. Based on the Ly
α
and UV LFs from our and previous studies, we find an increase of Ly
α
escape fraction
from
z
∼ 0 to 6 by two orders of magnitude. This large
increase can be explained neither by the evolution of stellar population nor by outflow alone, but by the evolution of neutral hydrogen
H
i
density in the interstellar medium that enhances dust attenuation for Ly
α
by resonance scattering. Our uniform expanding shell models suggest that the typical
H
i
column density decreases from
(
z
∼ 0) to ∼1 × 10
18
cm
−2
(
z
∼ 6) to explain the large
increase.
We report fourteen and twenty-eight protocluster candidates at z = 5.7 and 6.6 over 14 and 19 deg2 areas, respectively, selected from 2,230 Lyα emitters (LAEs) photometrically identified with ...Subaru/Hyper Suprime-Cam (HSC) deep images. Six out of the 42 protocluster candidates include at least 1 spectroscopically confirmed LAEs at redshifts up to z = 6.574. By the comparisons with the cosmological Lyα radiative transfer (RT) model reproducing LAEs with the reionization effects, we find that more than a half of these protocluster candidates might be progenitors of the present-day clusters with a mass of ≳ 1014M⊙. We also investigate the correlation between LAE overdensity and Lya rest-frame equivalent width (EW), because the cosmological Lyα RT model suggests that a slope of EW-overdensity relation is steepened towards the epoch of cosmic reionization (EoR), due to the existence of the ionized bubbles around galaxy overdensities easing the escape of Lyα emission from the partly neutral intergalactic medium. The available HSC data suggest that the slope of the EW-overdensity correlation does not evolve from the post-reionization epoch z = 5.7 to the EoR z = 6.6 beyond the moderately large statistical errors.
We present the ultra-deep Subaru narrowband imaging survey for Ly alpha emitters (LAEs) at z = 7.3 in the Subaru/XMM-Newton Deep Survey (SXDS) and Cosmic Evolution Survey (COSMOS) fields (~0.5deg ...super(2)) with a total integration time of 106 hr. Exploiting our new sharp bandwidth filter, NB101, installed on the Suprime-Cam, we have reached L(Ly alpha ) = 2.4 x 10 super(42) erg s super(-1) (5sigma) for z = 7.3 LAEs, about four times deeper than previous Subaru z gap 7 studies, which allows us to reliably investigate the evolution of the Ly alpha luminosity function (LF) for the first time down to the luminosity limit same as those of Subaru z = 3.1-6.6 LAE samples. Surprisingly, we only find three and four LAEs in the SXDS and COSMOS fields, respectively, while one expects a total of ~65 LAEs by our survey in the case of no Ly alpha LF evolution from z = 6.6 to 7.3.
Abstract
We detect 20
z
= 7.0 Ly
α
emitter (LAE) candidates to
L
(Ly
α
) ∼ 2 × 10
42
erg s
−1
or 0.3
L
z
=
7
*
and in a volume of 6.1 × 10
5
Mpc
3
in the Subaru Deep Field and the Subaru/
XMM-Newton
...Deep Survey field by 82 hr and 37 hr of Subaru Suprime-Cam narrowband NB973 and reddest optical
y
-band imaging. We compare their Ly
α
and UV luminosity functions (LFs) and densities and Ly
α
equivalent widths (EWs) to those of
z
= 5.7, 6.6, and 7.3 LAEs from previous Suprime-Cam surveys. The Ly
α
LF (density) rapidly declines by a factor of ×1.5 (1.9) in
L
(Ly
α
) at
z
= 5.7–6.6 (160 Myr), ×1.5 (1.6) at
z
= 6.6–7.0 (60 Myr) at the faint end, and ×2.0 (3.8) at
z
= 7.0–7.3 (40 Myr). Also, in addition to the systematic decrease in EW at
z
= 5.7–6.6 previously found, two-thirds of the
z
= 7.0 LAEs detected in the UV continuum exhibit lower EWs than the
z
= 6.6 ones. Moreover, while the UV LF and density do not evolve at
z
= 5.7–6.6, they modestly decline at
z
= 6.6–7.0, implying galaxy evolution contributing to the decline of the Ly
α
LF. Comparison of the
z
= 7.0 Ly
α
LF to the one predicted by an LAE evolution model further reveals that galaxy evolution alone cannot explain all of the decline of the Ly
α
LF. If we attribute the discrepancy to Ly
α
attenuation by neutral hydrogen, the intergalactic medium transmission of Ly
α
photons at
z
= 7.0 would be
T
Ly
α
IGM
≤
0.6
–
0.7
. It is lower (higher) than the
T
Ly
α
IGM
at
z
= 6.6 (7.3) derived by previous studies, suggesting rapid increase in neutral fraction at
z
> 6.
Abstract
Hyper Suprime-Cam (HSC) is a wide-field imaging camera on the prime focus of the 8.2-m Subaru telescope on the summit of Mauna Kea in Hawaii. A team of scientists from Japan, Taiwan, and ...Princeton University is using HSC to carry out a 300-night multi-band imaging survey of the high-latitude sky. The survey includes three layers: the Wide layer will cover 1400 deg2 in five broad bands (grizy), with a 5 σ point-source depth of r ≈ 26. The Deep layer covers a total of 26 deg2 in four fields, going roughly a magnitude fainter, while the UltraDeep layer goes almost a magnitude fainter still in two pointings of HSC (a total of 3.5 deg2). Here we describe the instrument, the science goals of the survey, and the survey strategy and data processing. This paper serves as an introduction to a special issue of the Publications of the Astronomical Society of Japan, which includes a large number of technical and scientific papers describing results from the early phases of this survey.
Abstract
The Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) is a three-layered imaging survey aimed at addressing some of the most important 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 2014 March. This paper presents the first public data release of HSC-SSP. This release includes data taken in the first 1.7 yr 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 (5 σ 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${^{\prime\prime}_{.}}$6 in the i band in the Wide layer. We show that we achieve 1%–2% point spread function (PSF) photometry (root mean square) both internally and externally (against Pan-STARRS1), and ∼10 mas and 40 mas internal and external astrometric accuracy, respectively. Both the calibrated images and catalogs are made available to the community through dedicated user interfaces and database servers. In addition to the pipeline products, we also provide value-added products such as photometric redshifts and a collection of public spectroscopic redshifts. Detailed descriptions of all the data can be found online. The data release website is https://hsc-release.mtk.nao.ac.jp.
Abstract
We study the UV luminosity functions (LFs) at z ∼ 4, 5, 6, and 7 based on the deep large-area optical images taken by the Hyper Suprime-Cam (HSC) Subaru Strategic Program (SSP). On the ...100 deg2 sky of the HSC SSP data available to date, we take enormous samples consisting of a total of 579565 dropout candidates at z ∼ 4–7 by the standard color selection technique, 358 out of which are spectroscopically confirmed by our follow-up spectroscopy and other studies. We obtain UV LFs at z ∼ 4–7 that span a very wide UV luminosity range of ∼0.002–100$\, L_{\rm UV}^\ast$ (−26 < MUV < −14 mag) by combining LFs from our program and the ultra-deep Hubble Space Telescope legacy surveys. We derive three parameters of the best-fit Schechter function, ϕ*, $M_{\rm UV}^{\,\ast}$, and α, of the UV LFs in the magnitude range where the active galactic nucleus (AGN) contribution is negligible, and find that α and ϕ* decrease from z ∼ 4 to 7 with no significant evolution of $M_{\rm UV}^{\,\ast}$. Because our HSC SSP data bridge the LFs of galaxies and AGNs with great statistical accuracy, we carefully investigate the bright end of the galaxy UV LFs that are estimated by the subtraction of the AGN contribution either aided by spectroscopy or the best-fit AGN UV LFs. We find that the bright end of the galaxy UV LFs cannot be explained by the Schechter function fits at >2 σ significance, and require either double power-law functions or modified Schechter functions that consider a magnification bias due to gravitational lensing.
Abstract
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 deg2 corresponding to 0.3–0.5 comoving Gpc2. We obtain the average large-scale bias values of bavg = 4.1 ± 0.2 (4.5 ± 0.6) at z = 5.7 (z = 6.6) for ≳ L* LAEs, indicating 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.
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