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SILVERRUSH. VIII. Spectroscopic Identifications of Early Large Scale Structures with Protoclusters Over 200 Mpc at z~6-7: Strong Associations of Dusty Star-Forming Galaxies

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Abstract

We have obtained three-dimensional maps of the universe in ~200x200x80 comoving Mpc^3 (cMpc^3) volumes each at z=5.7 and 6.6 based on a spectroscopic sample of 174 galaxies that achieves >~80% completeness down to the Lya luminosity of log(L_Lya/[erg s^-1])=43.0. The maps reveal filamentary large-scale structures and two remarkable overdensities made out of at least 42 and 12 galaxies at z=5.692 (z57OD) and z=6.585 (z66OD), respectively, making z66OD the most distant overdensity spectroscopically confirmed to date. We compare spatial distributions of submillimeter galaxies at z~4-6 with our z=5.7 galaxies forming the large-scale structures, and detect a 99.97% signal of cross correlation, indicative of a clear coincidence of dusty star-forming galaxy and dust unobscured galaxy formation at this early epoch. The galaxies in z57OD and z66OD are actively forming stars with star formation rates (SFRs) >~5 times higher than the main sequence, and particularly the SFR density in z57OD is 10 times higher than the cosmic average at the redshift (a.k.a. the Madau-Lilly plot). Comparisons with numerical simulations suggest that z57OD and z66OD are protoclusters that are progenitors of the present-day clusters with halo masses of ~10^14 Mo.
Accepted for Publication in The Astrophysical Journal
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SILVERRUSH. VIII. Spectroscopic Identifications of Early Large Scale
Structures with Protoclusters Over 200 Mpc at z67: Strong
Associations of Dusty Star-Forming Galaxies
Yuichi Harikane1,2,3, Masami Ouchi1,4, Yoshiaki Ono1, Seiji Fujimoto1,5 , Darko Donevski6,7, Takatoshi Shibuya8, Andreas L.
Faisst9, Tomotsugu Goto10, Bunyo Hatsukade11 , Nobunari Kashikawa5, Kotaro Kohno11, Takuya Hashimoto12,3, Ryo
Higuchi1,2, Akio K. Inoue12, Yen-Ting Lin13, Crystal L. Martin14 , Roderik Overzier15,16, Ian Smail17 , Jun Toshikawa1, Hideki
Umehata18,11, Yiping Ao19 , Scott Chapman20, David L. Clements21, Myungshin Im22 , Yipeng Jing23,24 , Toshihiro
Kawaguchi25, Chien-Hsiu Lee26 , Minju M. Lee27,3, Lihwai Lin13, Yoshiki Matsuoka28, Murilo Marinello15, Tohru Nagao29,
Masato Onodera26, Sune Toft29, Wei-Hao Wang13
1Institute for Cosmic Ray Research, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8582, Japan
2Department of Physics, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo, 113-0033, Japan
3National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
4Kavli Institute for the Physics and Mathematics of the Universe (WPI), University of Tokyo, Kashiwa 277-8583, Japan
5Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan
6Aix Marseille University, CNRS, LAM, Laboratoire dAstrophysique de Marseille, Marseille, France
7SISSA, via Bonomea 265, I-34136 Trieste, Italy
8Kitami Institute of Technology, 165 Koen-cho, Kitami, Hokkaido 090-8507, Japan
9Infrared Processing and Analysis Center, California Institute of Technology, MC 100-22, 770 South Wilson Ave., Pasadena, CA 91125,
USA
10 Institute of Astronomy, National Tsing Hua University, No. 101, Section 2, Kuang-Fu Road, Hsinchu, Taiwan
11 Institute of Astronomy, Graduate School of Science, The University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan
12 Department of Environmental Science and Technology, Faculty of Design Technology, Osaka Sangyo University, 3-1-1, Nagaito, Daito,
Osaka 574-8530, Japan
13 Institute of Astronomy & Astrophysics, Academia Sinica, Taipei 106, Taiwan (ROC)
14 Department of Physics, University of California, Santa Barbara, CA, 93106, USA
15 Observatorio Nacional, Rua Jose Cristino, 77. CEP 20921-400, Sao Cristovao, Rio de Janeiro-RJ, Brazil
16 Universidade de Sao Paulo, Instituto de Astronomia, Geof´ısica e Ciˆencias Atmosf´ericas, Departamento de Astronomia, S˜ao Paulo, SP
05508-090, Brazil
17 Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
18 RIKEN Cluster for Pioneering Research, 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan
19 Purple Mountain Observatory & Key Laboratory for Radio Astronomy, Chinese Academy of Sciences, 8 Yuanhua Road, Nanjing
210034, China
20 Department of Physics and Atmospheric Science, Dalhousie University, Halifax, NS B3H 3J5 Canada
21 Astrophysics Group, Imperial College London, Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK
22 CEOU/Astronomy Program, Dept. of Physics & Astronomy, Seoul National University, Seoul, Korea
23 School of Physics and Astronomy, Tsung-Dao Lee Institute, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai,
200240,China
24 IFSA Collaborative Innovation Center, Shanghai Jiao Tong University, Shanghai 200240, China
25 Department of Economics, Management and Information Science, Onomichi City University, Hisayamada 1600-2, Onomichi,
Hiroshima 722-8506, Japan
26 Subaru Telescope, NAOJ, 650 N Aohoku Pl, Hilo, HI 96720, USA
27 Division of Particle and Astrophysical Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya
464-8602, Japan
28 Research Center for Space and Cosmic Evolution, Ehime University, Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan and
29 Cosmic Dawn Center (DAWN), Niels Bohr Institute, Juliane Mariesvej 30, DK-2100 Copenhagen, Denmark
Accepted for Publication in The Astrophysical Journal
Abstract
We have obtained three-dimensional maps of the universe in 200×200×80 comoving Mpc3(cMpc3)
volumes each at z= 5.7 and 6.6 based on a spectroscopic sample of 179 galaxies that achieves &80%
completeness down to the Lyαluminosity of log(LLyα/[erg s1]) = 43.0, based on our Keck and Gemini
observations and the literature. The maps reveal filamentary large-scale structures and two remarkable
overdensities made out of at least 44 and 12 galaxies at z= 5.692 (z57OD) and z= 6.585 (z66OD),
respectively, making z66OD the most distant overdensity spectroscopically confirmed to date with
>10 spectroscopically confirmed galaxies. We compare spatial distributions of submillimeter galaxies
at z'46 with our z= 5.7 galaxies forming the large-scale structures, and detect a 99.97% signal of
cross correlation, indicative of a clear coincidence of dusty star-forming galaxy and dust unobscured
galaxy formation at this early epoch. The galaxies in z57OD and z66OD are actively forming stars
with star formation rates (SFRs) &5 times higher than the main sequence, and particularly the SFR
density in z57OD is 10 times higher than the cosmic average at the redshift (a.k.a. the Madau-Lilly
plot). Comparisons with numerical simulations suggest that z57OD and z66OD are protoclusters that
are progenitors of the present-day clusters with halo masses of 1014 M.
arXiv:1902.09555v2 [astro-ph.GA] 24 Jun 2019
2 Harikane et al.
Key words: galaxies: formation — galaxies: evolution — galaxies: high-redshift
1. Introduction
Galaxies are not uniformly distributed in the universe.
Some of them reside in groups and clusters on scales of
13 Mpc, while others lie in long filaments of galaxies
extending over 10 Mpc, called large scale structure (e.g.,
Gott et al. 2005). Investigating the large scale struc-
ture is important for understanding galaxy formation,
since there is observational evidence that galaxy proper-
ties depend on their environment. Indeed at low redshift,
galaxies in clusters are mostly passive, early-type galax-
ies (e.g., Dressler 1980; Goto et al. 2003), and there is
a clear trend that the star formation activity of galax-
ies tends to be lower in high-density environment than
low-density environment (Lewis et al. 2002; Tanaka et al.
2004), known as the morphology/star formation-density
relation. Since galaxies in dense environments appear to
experience accelerated evolution, we need to go to higher
redshifts to study the progenitors of low redshift high-
density environments.
Indeed, studies of the large scale structure at high red-
shift has shown that galaxies in dense regions experience
enhanced star formation (e.g., Kodama et al. 2001; El-
baz et al. 2007; Tran et al. 2010; Koyama et al. 2013),
opposite to the relation at low redshift. In addition, re-
cent cosmological simulations predict significant increase
of the contribution to the cosmic star formation density
from galaxy overdensities (Chiang et al. 2017). Thus,
many galaxy overdensities have been identified and in-
vestigated at z > 1 to date, including protoclusters that
grow to cluster-scale halos at the present day (e.g., Stei-
del et al. 1998, 2005; Shimasaku et al. 2003, 2004; Chiang
et al. 2014, 2015; Dey et al. 2016, see Overzier 2016 for a
review). At z > 3, since strong rest-frame optical emis-
sion lines are redshifted to mid-infrared, the Lyαemis-
sion line is used as a spectroscopic probe for galaxies.
Some of the high-redshift overdense regions are identi-
fied with UV continuum and/or Lyαemission lines (e.g.,
Overzier et al. 2006; Utsumi et al. 2010; Toshikawa et al.
2016; Pavesi et al. 2018; Higuchi et al. 2018), and spec-
troscopically confirmed with Lyα(e.g., Venemans et al.
2002; Ouchi et al. 2005; Dey et al. 2016; Jiang et al.
2018), including the galaxy overdensities at z= 6.01
(Toshikawa et al. 2012, 2014).
Since the Lyαphotons are easily absorbed by dust, it
is important to investigate whether dust-obscured galax-
ies are also residing in high-redshift overdensities traced
with the Lyαemission. In addition, dusty star forming
galaxies, such as submillimeter galaxies (SMGs), are ex-
pected to trace the most massive dark matter halos and
overdensities at z > 2 (e.g., Casey 2016; B´ethermin et al.
2017; Miller et al. 2018). Tamura et al. (2009) report 2.2σ
large scale correlation between SMGs and Lyαemitters
(LAEs) at z= 3.1 in the SSA22 protocluster. Umehata
et al. (2014) improve the selection of SMGs using photo-
metric redshifts, and detect stronger correlation between
SMGs and LAEs in the SSA22 protocluster (see also;
Umehata et al. 2015, 2017, 2018). These results suggest
that dust-obscured star forming galaxies are also lying
hari@icrr.u-tokyo.ac.jp
in the SSA22 protocluster traced by LAEs at z= 3.1.
However, the association between SMGs and LAEs at
higher redshift is not yet understood.
In this study, we investigate large scale structures at
z= 5.7 and 6.6 in the SXDS field using a large spec-
troscopic sample of 179 LAEs. Combined with our re-
cent Keck/DEIMOS and Gemini/GMOS observations,
we produce 3D maps of the universe traced with the
LAEs in two 200 ×200 ×80 cMpc3volumes at z= 5.7
and 6.6. We investigate the correlation between the
LAEs and dust-obscured high-redshift SMGs, and stel-
lar populations to probe the environmental dependence
of galaxy properties. We also compare our observational
results with recent numerical simulations. One of the
large scale structures investigated in this study is a pro-
tocluster at z= 5.7 firstly reported in Ouchi et al.
(2005). Ouchi et al. (2005) spectroscopically confirm 15
LAEs around this protocluster. Recently, Jiang et al.
(2018) study this protocluster with 46 spectroscopically-
confirmed LAEs in the SXDS field. In this study, we use
135 LAEs spectroscopically confirmed at z= 5.7, which
allows us to obtain more complete view of the 3D struc-
ture of this protocluster. In addition, we will investigate
the correlation with high-redshift SMGs that are not in-
vestigated in these studies. This study is one in a series
of papers from a program studying high redshift galax-
ies, named Systematic Identification of LAEs for Visi-
ble Exploration and Reionization Research Using Subaru
HSC (SILVERRUSH Ouchi et al. 2018). Early results
are already reported in several papers (Ouchi et al. 2018;
Shibuya et al. 2018a,b; Konno et al. 2018; Harikane et al.
2018b; Inoue et al. 2018; Higuchi et al. 2018).
This paper is organized as follows. In Section 2,
we present our LAE sample. We describe our spec-
troscopic observations in Section 3. We present our
results in Section 4, and in Section 5 we summarize
our findings. Throughout this paper we use the recent
Planck cosmological parameter sets constrained with the
temperature power spectrum, temperature-polarization
cross spectrum, polarization power spectrum, low-lpo-
larization, CMB lensing, and external data (TT, TE,
EE+lowP+lensing+ext result; Planck Collaboration
et al. 2016): m= 0.3089, ΩΛ= 0.6911, Ωb= 0.049,
h= 0.6774, and σ8= 0.8159. We assume a Chabrier
(2003) initial mass function (IMF) with lower and up-
per mass cutoffs of 0.1Mand 100M, respectively. All
magnitudes are in the AB system (Oke & Gunn 1983).
2. LAE Sample
We use LAE samples at z= 5.7 and 6.6 (Shibuya et al.
2018a) selected based on the Subaru/Hyper Suprime-
Cam Subaru strategic program (HSC-SSP) survey data
(Aihara et al. 2018a,b), reduced with the HSC data pro-
cessing pipeline (Bosch et al. 2017). The LAEs at z= 5.7
and 6.6 are selected with the narrowband filters, NB816
and NB921, which have central wavelengths of 8170 ˚
A
and 9210 ˚
A, and FWHMs of 131 ˚
A and 120 ˚
A to iden-
tify LAEs in the redshift range of z= 5.64 5.76 and
z= 6.50 6.63, respectively. The HSC-SSP survey has
three layers, UltraDeep (UD), Deep, and Wide, with dif-
Large Scale Structures with Protoclusters at z67 3
Figure 1. Overdensity maps of LAEs at z= 5.7 (left) and z= 6.6 (right). The black dots show the positions of the LAEs. The large dots
are LAEs whose NB magnitudes are brighter than 24.5 and 25.0 at z= 5.7 and 6.6, respectively. The blue contours show number densities
of LAEs brighter than 24.5 and 25.0 at z= 5.7 and 6.6, respectively. Higher density regions are indicated by the darker colors. The gray
regions are masked due to the survey edges and bright stars. The region indicated by the black polygon is the region where the fraction of
spectroscopically confirmed LAEs brighter than LLyα>1043 erg s1is &80 %.
ferent combinations of area and depth. In this study, we
use LAE samples in the UD-SXDS field, where rich spec-
troscopic data are available (see Section 3). 224 and 58
LAEs are selected at z= 5.7 and z= 6.6, respectively,
in the UD-SXDS field with the following color criteria:
z= 5.7 :
NB816 < N B8165σand iN B816 >1.2 and
g > g3σand [(rr3σand ri1.0) or r > r3σ],(1)
z= 6.6 :
NB921 < N B9215σand zN B921 >1.0 and
g > g3σand r > r3σand
[(zz3σand iz1.3) or z > z3σ].(2)
The subscripts “5σ” and “3σ” indicate the 5σand 3σ
magnitude limits for a given filter, respectively. Based
on spectroscopic observations in Shibuya et al. (2018b),
the contamination rate is 0 30%. In addition, we
use fainter LAE samples at z= 5.7 and 6.6 selected
with Subaru/Suprime-Cam images in Ouchi et al. (2008,
2010). The total numbers of LAEs are 563 and 247 at
z= 5.7 and 6.6, respectively.
To identify LAE overdensities, we calculate the galaxy
overdensity, δ, that is defined as follows:
δ=nn
n,(3)
where nis the number of LAEs in a cylinder and nis its
average. To draw two dimensional (2D) projected over-
density contours, we choose a cylinder whose height is
40 cMpc corresponding to the redshift range of the nar-
rowband selected LAEs at each redshift. The radius of
the cylinder is 0.07 deg which corresponds to 10 cMpc
at z6, which is a typical size of the protoclusters grow-
ing to 1015 Mhalo at z= 0 in simulations in Chiang
et al. (2013). We use LAEs brighter than NB816 <24.5
and NB921 <25.0 at z= 5.7 and 6.6, respectively,
to keep high detection completeness. The average num-
bers of LAEs in a cylinder are n= 0.48 and 0.26 at
z= 5.7 and 6.6, respectively. The masked regions are
excluded in the calculations. In Figure 1, we plot the
calculated overdensities smoothed with a Gaussian ker-
nel of σ= 0.07 deg. Here we define overdensities as
regions whose overdensity significances are higher than
4σlevels. We identify overdensities previously reported
in Higuchi et al. (2018); z6PCC1, z6PCC3, and z6PCC4
at z= 5.7, and z7PCC24 and z7PCC26 (see also Chan-
chaiworawit et al. 2017, 2019) at z= 6.6.1z6PCC1 is
the same structures reported in Ouchi et al. (2005) and
Jiang et al. (2018, see Section 4.1). Hereafter we refer to
z6PCC1 (n= 6, δ= 11.5, 7.2σ) and z7PCC24 (n= 4,
δ= 14.3, 6.8σ), the most overdense regions at z= 5.7
and 6.6 in the UD-SXDS field, as z57OD and z66OD,
respectively.
3. Spectroscopic Data
Out of 563 and 247 LAEs at z= 5.7 and 6.6, 135 and
36 LAEs are spectroscopically confirmed, respectively, in
previous studies (Ouchi et al. 2005, 2008, 2010; Shibuya
et al. 2018b; Harikane et al. 2018b; Higuchi et al. 2018;
Jiang et al. 2018). Four LAEs around z66OD, z66LAE-1,
-2, -3, and -4 are already spectroscopically confirmed. In
addition, we conducted Gemini and Keck spectroscopy
targeting LAEs of z66OD.
1We regard z7PCC26 as an overdensity following Higuchi et al.
(2018).
4 Harikane et al.
We used Gemini Multi-Object Spectrographs (GMOS)
on the 8m Gemini North telescope in 2017 and 2018. We
used a total of two GMOS masks with the OG515 filter
and R831 grating, and the total exposure times were 5400
and 10220 seconds. Our exposures were conducted with
spectral dithering of 50 ˚
A to fill CCD gaps. The spectro-
scopic coverage was between 7900 ˚
A and 10000 ˚
A. The
spatial pixel scale was 0.
000727 pixel1. The slit width
was 0.
0075 and the spectral resolution was R3000. The
seeing was around 0.
009. The reduction was performed us-
ing the Gemini iraf packages2. Wavelength calibration
was achieved by fitting to the OH emission lines.
We also used DEep Imaging Multi-Object Spectro-
graph (DEIMOS) on the 10m Keck II telescope in 2018.
We used one DEIMOS mask covering nine LAEs in
z66OD, and the OG515 filter and R831 grating, and
the total exposure times were 5400 and 10220 seconds.
We used one DEIMOS mask with the OG550 filter and
830G grating, and the total exposure time was 4900 sec-
onds. The spectroscopic coverage was between 6000 ˚
A
and 10000 ˚
A. The spatial pixel scale was 0.
001185 pixel1.
The slit width was 0.
008 and the spectral resolution was
R3000. The seeing was around 0.
008. The reduction
was performed using the spec2d IDL pipeline developed
by the DEEP2 Redshift Survey Team (Davis et al. 2003).
Wavelength calibration was achieved by fitting to the arc
lamp emission lines.
In these observations, we identified emission lines in
eight LAEs, z66LAE-5, -6, -7, -8, -9, -10, -11 and -12.
We evaluate asymmetric profiles of these emission lines
by calculating the weighted skewness, Sw(Kashikawa
et al. 2006). We find that the weighted skewness values
of the lines in six LAEs, z66LAE-5, -6, -7, -8, -10, and
-11 are larger than 3, indicating that these asymmetric
lines are Lyα. The weighted skewness values of the lines
in z66LAE-9 and z66LAE-12 are less than 3. The narrow
emission lines (FWHM '200 km s1after a correction
for the instrumental broadening) and medium spectral
resolution (R3000) do not suggest that these emis-
sion lines are [Oii]λλ3726,3729. We do not find signifi-
cant emission lines except for these lines at 9190 and
9250 ˚
A, rejecting the possibility of [Oiii]λ5007 emit-
ters with detectable [Oiii]λ4959 or Hβlines, or Hαemit-
ters with a detectable [Oiii]λ5007 line. Since most un-
resolved single line emitters have been found to be LAEs
with a moderate velocity dispersion (Hu et al. 2004), we
regard these lines as Lyα. Note that removing z66LAE-
9 and z66LAE-12 from our analysis does not change our
conclusions.
Thus total of 135 and 44 LAEs at z= 5.7 and 6.6 are
used in this study. Figure 2 shows the numbers of LAEs
spectroscopically confirmed and their fractions. Thanks
to the large spectroscopic sample, the fraction of the
spectroscopically confirmed LAEs is &80 % down to
the Lyαluminosity of LLyα= 1043 erg s1at z= 5.7
and 6.6 in the regions indicated with the black polygon
in Figure 1, corresponding to the SXDS fields in Ouchi
et al. (2008, 2010). Although the spectroscopic fraction
of z57OD (88% for LLyα>1043 erg s1) is higher than
that of all z= 5.7 LAEs (77% for LLyα>1043 erg s1),
2https://www.gemini.edu/sciops/data-and-results/processing-
software
Figure 2. Upper panel: Number of LAEs with spectroscopic
confirmations. The blue and red histograms show cumulative num-
bers of all LAEs (open histogram) and spectroscopically confirmed
LAEs (hatched histogram) in the black pentagon in Figure 1 at
z= 5.7 and 6.6, respectively. Lower panels: Fraction of spec-
troscopically confirmed LAEs at z= 5.7 and 6.6. The blue and
red solid curves show cumulative fractions of spectroscopically con-
firmed LAEs in the black pentagon in Figure 1 at z= 5.7 and 6.6,
respectively.
the difference (10%) is not significant for our identifi-
cations of the overdensities in Section 4.1. We do not find
strong AGN signatures, such as the broad Lyαemission
lines nor Nv1240 lines, in the spectra of our LAEs.
4. Results and Discussions
4.1. Large Scale Structure at z= 5.7and z= 6.6and
Spectroscopic Confirmation of z66OD at z= 6.585
We obtain the three-dimensional (3D) map using the
179 spectroscopic confirmed LAEs. We calculate the 3D
overdensity using the LAE sample with a sphere whose
radius is 10 cMpc (15 cMpc) at z= 5.7 (z= 6.6). Note
that velocity offsets of the Lyαemission lines to the sys-
temic redshifts are typically 300 km s1or 2.5 cMpc
(e.g., Erb et al. 2014; Faisst et al. 2016; Hashimoto et al.
2018), smaller than the radius of the sphere. In Figure 3,
we plot the locations of the LAEs and the 3D overden-
sity smoothed with a Gaussian kernel of σ= 10 cMpc
(15 cMpc) at z= 5.7 (z= 6.6). Figure 4 shows the 2D
maps with the redshift slices of ∆z0.02. These maps
reveal the filamentary 3D large scale structures made by
Large Scale Structures with Protoclusters at z67 5
z57OD
z66OD
Figure 3. 3D overdensity maps of LAEs at z= 5.7 (left) and z= 6.6 (right). The black dots show the positions of the LAEs. The large
dots are LAEs brighter than LLyα>1043 erg s1. Higher density regions are indicated by the bluer colors, smoothed with a Gaussian
kernel of σ= 10 cMpc (15 cMpc) at z= 5.7 (z= 6.6).
Figure 4. Two-dimensional map of LAEs at z= 5.7 (upper) and z= 6.6 (lower) with the redshift slices. The black dots show the
positions of the LAEs in the ∆z0.02 redshift depth. The large dots are LAEs brighter than LLyα>1043 erg s1. Higher density regions
are indicated by the darker colors, smoothed with a Gaussian kernel of σ= 10 cMpc (15 cMpc) at z= 5.7 (z= 6.6).
the LAEs at z= 5.7 and 6.6.
In the 3D maps, we identify z57OD (z= 5.692) and
z66OD (z= 6.585) with 44 and 12 LAEs spectroscop-
ically confirmed, respectively, which are located within
1σcontours in Figures 5 and 6. The 1σcontours are
roughly corresponding to the 20 cMpc-radius aperture.
According to theoretical studies in Chiang et al. (2017),
the 20 cMpc-radius aperture at z6 includes >90%
members of clusters at z= 0. We include z66LAE-8 lo-
cated just outsize the 1σcontour, because it is within 20
cMpc from the center of z66OD. Figures 5 and 6 show
the locations of LAEs, 2D projected contours, and spec-
tra of the LAEs of z57OD and z66OD, respectively. Ta-
bles 1 and 2 summarize properties of LAEs of z57OD and
z66OD, respectively. The average redshift of the LAEs
of z66OD (z= 6.585) suggests that z66OD is the most
distant overdensity with >10 galaxies spectroscopically
confirmed to date (c.f., 3 galaxies at z= 7.1 in Castel-
lano et al. 2018). Properties of overdensities in this work
and in the literature are summarized in Table 3, which is
based on objects listed in Table 5 in Chiang et al. (2013)
and new objects discovered since.
Both z57OD and z66OD are located in the filamen-
tary structures made by LAEs around these overdensi-
ties, extending over 40 cMpc. We evaluate the extension
of these overdensities in the redshift direction by cal-
culating velocity dispersions of LAEs. We select LAEs
within 0.07 deg from the centers (defined as the highest
density peaks) of z57OD and z66OD, and calculate the
rms of their velocities as velocity dispersions. The cal-
culated velocity dispersions are 1280 ±220 km s1and
670 ±200 km s1, respectively, similar to the value of
galaxies in overdensities found in Lemaux et al. (2017,
1038 ±178 km s1) and Toshikawa et al. (2012, 647 ±
124 km s1), respectively. These velocity dispersions are
compared with simulations in Section 4.2.
Jiang et al. (2018) identify SXDS gPC in their spec-
troscopic survey. Since the coordinate and redshift of
SXDS gPC are the same as those of z57OD, we con-
clude that SXDS gPC is the same structure as z57OD.
6 Harikane et al.
Table 1
Spectroscopically Confirmed LAEs of z57OD
ID R.A.(J2000) Decl.(J2000) zspec logLLyαMUV E W 0
LyαRef.
(1) (2) (3) (4) (5) (6) (7) (8)
z57LAE-1 02:17:48.46 05:31:27.02 5.688 43.06+0.04
0.05 20.9+0.3
0.254+22
13 O08
z57LAE-2 02:17:55.83 05:30:26.94 5.694 42.57+0.10
0.13 18.9+1.1
1.186+162
38 Hi18
z57LAE-3 02:17:51.14 05:30:03.64 5.711 42.74+0.08
0.10 19.6+0.8
0.786+103
43 O08
z57LAE-4 02:17:49.11 05:28:54.17 5.695 43.17+0.03
0.04 19.8+0.8
0.6193+206
83 O08
z57LAE-5 02:17:45.24 05:29:36.01 5.687 43.09+0.04
0.04 >19.4>216 O08
z57LAE-6 02:17:48.19 05:28:51.92 5.690 42.59+0.09
0.12 18.9+1.1
1.199+200
49 Hi18
z57LAE-7 02:17:45.01 05:28:42.37 5.751 42.71+0.09
0.11 20.7+0.2
0.230+12
8O08
z57LAE-8 02:17:42.17 05:28:10.55 5.679 42.91+0.06
0.07 20.8+0.2
0.246+16
11 Hi18
z57LAE-9 02:17:36.68 05:30:27.57 5.686 42.53+0.11
0.14 18.9+1.1
1.188+156
46 Hi18
z57LAE-10 02:17:22.28 05:28:05.30 5.681 42.76+0.06
0.08 18.9+1.1
1.1151+228
69 Hi18
z57LAE-11 02:17:57.66 05:33:09.16 5.749 42.75+0.10
0.12 20.0+0.6
0.666+89
29 Hi18
z57LAE-12 02:17:29.18 05:30:28.50 5.746 42.48+0.13
0.19 19.1+1.0
1.066+124
36 Hi18
z57LAE-13 02:16:54.60 05:21:55.53 5.712 43.10+0.04
0.04 20.1+0.7
0.5127+129
48 Hi18
z57LAE-14 02:17:04.30 05:27:14.30 5.686 43.15+0.04
0.04 20.3+0.6
0.4119+102
40 Hi18
z57LAE-15 02:17:07.85 05:34:26.51 5.678 43.24+0.03
0.03 20.6+0.4
0.3113+64
31 Hi18
z57LAE-16 02:17:24.02 05:33:09.62 5.707 43.32+0.02
0.02 21.3+0.2
0.275+20
14 Hi18
z57LAE-17 02:18:03.87 05:26:43.45 5.747 42.90+0.06
0.07 >19.4>136 Hi18
z57LAE-18 02:18:04.17 05:21:47.25 5.734 42.87+0.06
0.08 21.4+0.2
0.223+7
5Hi18
z57LAE-19 02:18:05.17 05:27:04.06 5.746 42.89+0.06
0.07 >19.4>133 Hi18
z57LAE-20 02:18:05.28 05:20:26.89 5.742 42.80+0.08
0.09 20.5+0.5
0.344+33
16 Hi18
z57LAE-21 02:18:28.87 05:14:23.01 5.737 43.38+0.02
0.02 20.4+0.6
0.4198+161
64 Hi18
z57LAE-22 02:18:30.53 05:14:57.80 5.688 43.27+0.03
0.03 20.4+0.6
0.4154+124
50 Hi18
z57LAE-23 02:17:13.81 05:35:58.23 5.686 42.86+0.09
0.11 21.0+0.3
0.333+15
10 Hi18
z57LAE-24 02:18:00.70 05:35:18.92 5.673 43.04+0.05
0.06 21.6+0.1
0.128+6
5Hi18
z57LAE-25 02:17:58.09 05:35:15.35 5.681 42.55+0.11
0.14 19.0+1.0
1.082+134
41 Hi18
z57LAE-26 02:17:14.93 05:35:02.77 5.685 42.50+0.12
0.17 20.6+0.2
0.220+10
7Hi18
z57LAE-27 02:17:34.16 05:34:52.56 5.708 42.63+0.09
0.11 18.9+1.1
1.1105+221
48 Hi18
z57LAE-28 02:17:16.10 05:34:24.23 5.693 42.73+0.08
0.10 19.1+1.1
1.1118+239
59 Hi18
z57LAE-29 02:17:05.63 05:32:17.66 5.645 42.89+0.08
0.09 20.7+0.3
0.348+27
14 Hi18
z57LAE-30 02:17:15.53 05:32:14.04 5.685 42.51+0.11
0.15 19.9+0.4
0.438+31
15 Hi18
z57LAE-31 02:17:38.28 05:30:48.70 5.687 42.86+0.07
0.09 19.9+0.6
0.685+90
33 Hi18
z57LAE-32 02:17:01.13 05:29:28.40 5.665 42.53+0.12
0.17 19.1+1.1
1.172+141
39 Hi18
z57LAE-33 02:17:09.50 05:27:31.49 5.674 42.71+0.08
0.10 19.1+1.1
1.1125+235
66 Hi18
z57LAE-34 02:17:07.96 05:27:23.16 5.720 42.52+0.12
0.17 19.1+1.1
1.168+136
36 Hi18
z57LAE-35 02:17:49.99 05:27:08.07 5.693 43.08+0.06
0.07 20.3+0.6
0.6104+116
40 O08
z57LAE-36 02:17:36.38 05:27:01.62 5.672 43.16+0.04
0.05 20.2+0.5
0.5136+105
47 Hi18
z57LAE-37 02:17:09.95 05:26:46.53 5.689 42.91+0.07
0.09 19.4+1.1
1.1126+230
58 Hi18
z57LAE-38 02:17:45.19 05:25:57.75 5.647 42.59+0.11
0.15 19.7+0.6
0.656+68
26 Hi18
z57LAE-39 02:16:59.94 05:23:05.33 5.700 42.49+0.12
0.16 19.8+0.5
0.540+40
17 Hi18
z57LAE-40 02:16:57.88 05:21:16.99 5.667 43.16+0.04
0.04 19.7+0.8
0.8210+311
89 Hi18
z57LAE-41 02:18:02.18 05:20:11.48 5.718 42.59+0.09
0.12 18.9+1.1
1.199+167
49 Hi18
z57LAE-42 02:17:01.43 05:18:41.68 5.679 42.71+0.08
0.09 19.0+1.1
1.1118+202
55 Hi18
z57LAE-43 02:17:00.61 05:31:30.27 5.754 42.56+0.11
0.14 20.0+0.5
0.544+39
18 J18
z57LAE-44 02:17:52.63 05:35:11.79 5.759 43.49+0.02
0.02 22.1+0.1
0.150+6
5J18
Note. — (1) Ob ject ID. (2) Right ascension. (3) Declination. (4) Spectroscopic redshift of
the Lyαemission line. (5) Lyαluminosity in units of erg s1. (6) Absolute UV magnitude or its
2σlower limit in units of ABmag. (7) Rest-frame LyαEW or its 2σlower limit in units of ˚
A.
(8) Reference (O08:Ouchi et al. 2008, Hi18:Higuchi et al. 2018, J18:Jiang et al. 2018).
Large Scale Structures with Protoclusters at z67 7
Figure 5. Left panel: 3D distribution of LAEs of z57OD. The large dots are LAEs whose NB magnitudes are brighter than 24.5. The
LAEs indicated with the black squares are spectroscopically confirmed. The crosses are spectroscopically confirmed LAEs in Jiang et al.
(2018) but not identified in our photometric catalog. The numbers denote IDs of the LAEs. The cyan contour shows the significance levels
of the overdensity from 1σto 5σ. The red circles are the red SMGs (see Section 4.3), and the red crosses show the positions of the ALMA
counterparts of the SMGs. Right panel: Examples of spectra of LAEs of z57OD. The y-axes range of the 2D spectra are ±500. The y-axes
in the 1D spectra are arbitrary.
8 Harikane et al.
Figure 6. Same as Figure 5 but for z66OD. The large dots are LAEs whose NB magnitudes are brighter than 25.0. The signals in the
2D spectra of z66LAE-4 (9270 ˚
A) and z66LAE-8 (9160 ˚
A) are residuals of the sky subtractions.
Jiang et al. (2018) spectroscopically confirm 46 LAEs at
z= 5.7 in the UD-SXDS field. 34 LAEs among the 46
LAEs overlap with our LAE catalog, and traces simi-
lar large scale structures to the ones we identify. How-
ever, the overdensity value and its significance (δ= 5.6,
5σ) are different from our measurements (δ= 15.0,
8.4σ). This is because the aperture size and magnitude
limit of LAEs for the δcalculation are different between
our measurements (10 cMpc-radius circular aperture and
24.5 mag) and Jiang et al. (352cMpc2aperture and 25.5
mag). If we calculate by adopting the same aperture size
and magnitude limit as Jiang et al. (2018) for spectro-
scopically confirmed LAEs, we obtain δ= 4.8 (4.1σ),
comparable to the measurements of Jiang et al. (2018).
4.2. Comparison with Simulations
We compare our results with numerical simulations of
Inoue et al. (2018) to estimate halo masses of z57OD
and z66OD. Inoue et al. (2018) use N-body simulations
with 40963dark matter particles in a comoving box of
162 Mpc. The particle mass is 2.46×106Mand the min-
imum halo mass is 9.80 ×107M. Halos’ ionizing emis-
sivity and IGM Hi clumpiness are produced by a RHD
simulation with a 20 comoving Mpc3box (Hasegawa et
al. in prep.). LAEs have been modeled with phys-
ically motivated analytic recipes as a function of halo
mass. LAEs are modeled based on the radiative trans-
fer calculations by a radiative hydrodynamic simulation
(Hasegawa et al in prep.). In this work, we use the LAE
model G with the late reionization history, which repro-
duces all observational results, namely the neutral hy-
drogen fraction measurements, Lyαluminosity functions,
LAE angular correlation functions, and Lyαfractions in
LBGs at z&6. Thus we expect that similar systems
to z57OD and z66OD are found in the simulations. We
slice the 162 ×162 ×162 cMpc3box into four slices of
162×162×40.5 cMpc3whose depth (40 cMpc) is com-
parable to the redshift range of the narrowband selected
Large Scale Structures with Protoclusters at z67 9
Table 2
Spectroscopically Confirmed LAEs of z66OD
ID R.A.(J2000) Decl.(J2000) zspec logLLyαMUV E W 0
LyαRef.
(1) (2) (3) (4) (5) (6) (7) (8)
z66LAE-1 02:17:57.58 05:08:44.64 6.595 43.48+0.02
0.03 21.4+0.6
0.491+68
29 O10
z66LAE-2 02:18:20.69 05:11:09.88 6.575 42.96+0.07
0.09 >19.9>59 O10
z66LAE-3 02:18:19.39 05:09:00.65 6.563 42.95+0.07
0.09 20.8+0.8
0.649+60
25 O10
z66LAE-4 02:18:43.62 05:09:15.63 6.513 43.04+0.06
0.08 22.0+0.3
0.220+10
6Ha18
z66LAE-5 02:18:18.73 05:04:12.96 6.599 42.98+0.07
0.08 20.9+0.8
0.650+59
25 This work
z66LAE-6 02:18:27.00 05:07:26.89 6.553 42.99+0.06
0.08 >20.5>66 This work
z66LAE-7 02:18:27.95 05:06:29.89 6.597 42.76+0.16
0.26 21.8+0.6
0.614+27
8This work
z66LAE-8 02:17:56.99 05:04:14.33 6.570 42.85+0.09
0.12 >20.1>59 This work
z66LAE-9 02:18:00.79 05:03:30.25 6.613 42.43+0.24
0.57 >20.2>19 This work
z66LAE-10 02:18:00.23 05:03:46.73 6.601 42.60+0.14
0.21 >20.0>42 This work
z66LAE-11 02:17:56.42 05:16:37.96 6.559 42.76+0.13
0.19 21.1+0.8
0.822+74
13 This work
z66LAE-12 02:17:57.30 05:15:56.27 6.564 42.52+0.20
0.39 >20.2>32 This work
Note. — (1) Object ID. (2) Right ascension. (3) Declination. (4) Spectroscopic redshift of the
Lyαemission line. (5) Lyαluminosity in units of erg s1. (6) Absolute UV magnitude or its 2σlower
limit in units of ABmag. (7) Rest-frame LyαEW or its 2σlower limit in units of ˚
A. (8) Reference
(O10:Ouchi et al. 2010, Ha18:Harikane et al. 2018b).
LAEs at z= 5.7 and 6.6. Magnitudes of the LAEs are
calculated based on the transmission curves of the HSC
filters.
We select z= 5.7 and 6.6 mock LAEs with i
NB816 >1.2 and zN B921 >1.0, which are the
same as our color criteria of Equations (1) and (2),
respectively. Then we use mock LAEs brighter than
NB816 <24.5 mag and NB921 <25.0 mag at z= 5.7
and 6.6, respectively, and calculate the galaxy overden-
sity in each slice with a cylinder whose depth and radius
are 40 cMpc and 10 cMpc, respectively. The average
number densities of LAEs in the cylinder are n= 0.39
and 0.32 at z= 5.7 and 6.6, respectively, which agree
with observations within 1σfluctuations. We show the
calculated overdensity in each slice in Figure 7. We define
overdensities as regions whose overdensity significances
are higher than 4σ. We calculate velocity dispersions of
LAEs in the overdensities, using LAEs within 10 cMpc
from the centers of the overdensities, similar aperture size
to the one used in the velocity dispersion calculations for
z57OD and z66OD.
We compare the significances and velocity dispersions
of the overdensities in the simulations with z57OD and
z66OD in Figure 8. At z= 5.7, we find three over-
densities, simOD1 (δ= 19.5, 10.8σ,σV= 1100 km s1),
simOD2 (δ= 11.8, 6.6σ,σV= 750 km s1), and simOD3
(δ= 9.3, 5.1σ,σV= 1500 km s1), whose significance
and velocity dispersion are comparable with z57OD with
.2σuncertainties. The masses of the most massive
halos in these three overdensities are 1.0×1012 M,
4.7×1011 M, and 7.7×1011 M, respectively, at
z= 5.7. At z= 6.6, we identify one overdensity, simOD4
(δ= 13.7, 7.3σ,σV= 610 km s1), whose significance
and velocity dispersion are comparable with z66OD with
.1σuncertainties. The mass of the most massive halo
in simOD4 is 3.9×1011 Mat z= 6.6. Since the sim-
ulations do not go to z0, we use the extended Press-
Schechter model of Hamana et al. (2006) to estimate the
present-day halo masses of the z= 5.7 and 6.6 halos. We
find that these four overdensities in the simulations will
grow to the cluster-scale halo (Mh1014 M) at z0
with scatters of 1 dex in Mh, indicating that z57OD
and z66OD are protoclusters. Note that Overzier et al.
(2009) reached the same conclusion on the progenitor of
z57OD.
We also estimate present-day halo masses of z57OD
and z66OD using another method following previous
studies (Steidel et al. 1998; Venemans et al. 2005;
Toshikawa et al. 2012). The halo mass at z= 0 of a
protocluster Mhis given by
M= ¯ρV (1 + δm),(4)
where ¯ρ= 4.1×1010 MMpc3is the mean matter
density of the universe, Vis the comoving volume of the
protocluster that collapses into the cluster at z= 0, and
δmis the mass overdensity. The mass overdensity δmis
related to the galaxy overdensity δwith
1 + m=C(1 + δ),(5)
where bis the bias factor of galaxies and Cis the correc-
tion factor for the redshift space distortion. We assume
C= 1 because this value is close to 1 at high redshift
(Lahav et al. 1991). The biases of LAEs at z= 5.7 and
6.6 are estimated to be b= 4.1 and b= 4.5 in Ouchi
et al. (2018). Assuming V= (4/3)π×103Mpc3(typical
size of a protocluster in Chiang et al. 2013), we estimate
the present-day halo masses of z57OD and z66OD to be
4.8×1014 Mand 5.4×1014 M, which agree with
simulations. These estimated present-day halo masses
support that z57OD and z66OD are protoclusters.
As discussed in the previous paragraph, we identify
similar overdensities to z57OD in the simulation. How-
ever, Jiang et al. (2018) report that they do not find
overdensities similar to z57OD in their cosmological sim-
ulation that is an update of a previous work (Chiang
et al. 2013). This difference may be due to the different
sizes of apertures used to search overdensities. We use 10
cMpc-radius circular aperture, while Jiang et al. (2018)
use a larger, 352cMpc2aperture. Thus the simulations
could reproduce overdensities in the small scale, while
10 Harikane et al.
Figure 7. Upper panels: 2D map of LAEs at z= 5.7 for four slices in the simulation box. Each slice has the 40 cMpc depth
corresponding to the narrowband width. The black dots show the positions of the LAEs with N B816 <25.5 mag. The large dots are
LAEs brighter than NB 816 <24.5 mag. Lower panels: Same as the upper panels but at z= 6.6. The large dots are LAEs brighter than
NB921 <25.0 mag.
Figure 8. Velocity dispersion of LAEs of overdensities as a func-
tion of the overdensity significance for LAEs at z= 5.7 (left) and
z= 6.6 (right). The red squares show z57OD (left) and z66OD
(right). The black and gray circles denote the overdensities iden-
tified in the simulations. We identify three and one overdensities
in simulations whose properties are similar to z57OD and z66OD,
respectively.
could not in the large scale.
4.3. Correlation with Red SMGs
In Section 4.1, we identify the large scale structures
made by LAEs, typically dust-poor star-forming galaxies.
It is important to investigate whether dust-obscured star-
formation also traces the large scale structures. We select
high-redshift SMGs at z'46 (hereafter red SMGs)
from the JCMT/SCUBA-2 Cosmology Legacy Survey
850 µm source catalog (Geach et al. 2017) using Her-
schel/SPIRE fluxes. It should be noted that 850 µm
offers the negative K-correction to study SMGs with the
same sensitivity at z6 as at the z= 2 3.
To estimate Herschel/SPIRE fluxes and partially over-
come confusion problem due to the large beam size,
we apply de-blending approach by using higher resolu-
tion positional priors. We adopt positions of SCUBA-2
sources detected with >4σtotal noise and then apply si-
multaneous source-fitting routine available via SUSSEX-
tractor task in HIPE (Ott 2010; Savage & Oliver 2007).
The PSF of the JCMT/SCUBA-2 image is 14.
008 (Geach
et al. 2017). The PSFs of the Herschel/SPIRE images are
assumed to be Gaussian with FWHM being 17.
006, 25.
001
and 35.
002 at 250 µm, 350 µm, and 500 µm respectively.
Total flux uncertainties are estimated by quadratically
adding the instrument and confusion noise. We further
fully evaluate our selection via realistic end-to-end simu-
lation based on galaxy model of B´ethermin et al. (2017)
which includes physical clustering based on abundance
matching and galaxy-galaxy lensing. Using this simula-
tion, we simulate the exact criteria we applied on our
real maps. The typical flux density error is 9 mJy at
500µm, which is in agreement with a value predicted by
simulations.
To select red SMGs, we adopt the following criteria
(Donevski et al. 2018):
S250µm< S350µm< S500µm(6)
where S250µm,S350µm, and S500µmare the Herschel
250 µm, 350 µm, and 500 µm fluxes, respectively. Equa-
tion (6) allows us to select z&4 SMGs whose modified
Large Scale Structures with Protoclusters at z67 11
Figure 9. Left panel: Locations of the red-SMGs and LAEs at z= 5.7. The red filled circles show the red SMGs and their sizes
are scaled with the 850 µm fluxes of the SMGs. The black circles are the LAEs at z= 5.7, and the large circles show bright LAEs with
NB816 <24.5. The black and red contours shows the significance levels of the overdensity from 1σto 4σfor z= 5.7 LAEs and red
SMGs, respectively. Right panel: Clustering of different popullations. The red filled (open) squares show the CCFs between the all
(spectroscopically confirmed) LAEs at z= 5.7 and red SMGs. The blue upper limits are the CCFs between the z= 5.7 LAEs and the blue
SMGs. The black circles show the ACFs of the z= 5.7 LAEs for reference. We detect significant cross correlation signal between z= 5.7
LAEs and red SMGs, indicating that a large number of the red SMGs are residing at z= 5.7.
black body emission peak at >500 µm (see Figure 6
in Donevski et al. 2018).3When using Equation (6), we
adopt the following three criteria to measure the Herschel
colors correctly. First, we use only sources whose 500 µm
fluxes are measured at >2σlevels. Second, if the sources
are not detected in the 250 µm and/or 350 µm bands
at the 2σlevels, we replace fluxes with 2σflux limits.
Third, we remove sources that are detected in 250 µm but
not in 350 µm. After adopting these criteria and Equa-
tion (6), we reduce low-redshift interlopers using ALMA
and Subaru/HSC data. We cross-match the SCUBA-2
sources with ALMA sources in archival data (see also
Stach et al. 2018) within 1000, and identify ALMA coun-
terparts of the SCUBA-2 sources if present. The ALMA
data we use are taken in band 7, with typical 1σnoise
level and angular resolution are 0.2 mJy/beam and 0.
002,
respectively. We identify ALMA counterparts of more
than 70% of the SCUBA-2 sources, and most of the rest
are not observed with ALMA. We then measure fluxes
at the positions of the ALMA counterparts in the HSC g
and rimages, and exclude SCUBA-2 sources with detec-
tion at >3σlevels in the HSC gor rband images (bluer
than the Lyman break at z'46). Finally, we apply
masks of diffraction spikes and halos from bright objects
in the same fashion as for our LAEs, and obtain the final
red SMG sample. We also define SMGs not selected with
above criteria as blue SMGs, which will be used for a null
test. In addition, we select LAEs at z= 5.7 located in
the sky coverage of the SCUBA-2 observation. Finally
we obtain 44 red SMGs, 673 blue SMGs, and 227 LAEs
(77 spectroscopically confirmed). Note that there is no
3Although Donevski et al. (2018) showed that most of the galax-
ies lie at z < 5, this is because the number density of z > 5 SMG
is low (e.g., Ivison et al. 2016).
overlap between the LAEs and the ALMA sources within
200. Since LAEs are typically dust-poor weak 850 µm and
[Cii]158µm emitters (Harikane et al. 2018b), finding no
overlap is reasonable. According to Geach et al. (2017),
the false detection rate is <6% at the >4σdetection.
Since we will test whether the red SMGs are at z= 5.7
or not by the cross-correlation analysis later, we do not
take this false detection rate into account here.
The left panel in Figure 9 shows locations of the
red SMGs and z= 5.7 LAEs. We find that some of
the red SMGs are clustering around z57OD (R.A.=
34.26,decl.=5.54). We calculate the cross-correlation
function (CCF) of the 227 LAEs at z= 5.7 and the 44
red SMGs using the estimator in Landy & Szalay (1993):
ω(θ) = D1D2(θ)D1R2(θ)R1D2(θ) + R1R2(θ)
R1R2(θ),
(7)
where DD,DR,RD, and RR are the numbers of galaxy-
galaxy, galaxy-random, random-galaxy, and random-
random pairs for the group 1 and 2. We also calculate the
CCF between the 77 spectroscopically confirmed LAEs
and red SMGs, the CCF between the 227 LAEs and
775 blue SMGs, and angular auto-correlation functions
(ACFs) of the 227 LAEs for reference. Using SCUBA-2
SMGs may have the blending bias effect on the correla-
tion function measurements due to confusion introduced
by the coarse angular resolution (Karim et al. 2013; Stach
et al. 2018). However, the effect is expected to be small,
a factor of 1.21.3 (Cowley et al. 2017). We esti-
mate statistical errors of the CCFs and ACF using the
Jackknife estimator. We divide the samples into 47 Jack-
knife subsamples of about 5002arcsec2, comparable to
the maximum angular size of the correlation function
12 Harikane et al.
measurements. Removing one Jackknife subsample at
a time for each realization, we compute the covariance
matrix as
Cij =N1
N
N
X
l=1
ωl(θi)¯ω(θi) ωl(θj)¯ω(θj).(8)
where Nis the total number of the Jackknife samples,
and ωlis the estimated CCFs or ACF from the lth real-
ization. ¯ωdenotes the mean CCFs and ACF. We apply a
correction factor (typically 1.1) given by Hartlap et al.
(2007) to an inverse covariance matrix in order to com-
pensate for the bias introduced by the statistical noise.
The calculated CCFs and ACF are presented in the
right panel of Figure 9. We detect the signal of the cross-
correlation between the LAEs at z= 5.7 and red SMGs.
We evaluate the significance of the correlation by calcu-
lating the χ2value,
χ2=X
i.j
[ω(θi)ωmodel(θi)] C1
i,j [ω(θj)ωmodel(θj)] ,
(9)
where ωmodel = 0 for the non-detection case. We obtain
χ2= 13.0, indicating the 99.97% significance correla-
tion. If we use the spectroscopically confirmed LAEs,
the significance level of the cross-correlation is still 96%.
We do not detect the >2σcorrelation signal between
the LAEs and blue SMGs, nor the LAEs and all SMGs.
These significant correlations between the LAEs and red
SMGs indicate that the red SMGs also trace the large
scale structure with z57OD made by the LAEs, similar
to the SSA-22 protocluster at z= 3.1 (Tamura et al.
2009; Umehata et al. 2014). We also calculate cross cor-
relation functions between the LAEs at z= 6.6 and red
SMGs, but do not detect a significant correlation signal
beyond 2σ.
We evaluate the fraction of the red SMGs located at
z= 5.7. If all of the SMGs and LAEs are at z= 5.7, the
large scale (&1 cMpc) amplitude of the CCF between
the LAEs and red SMGs is expressed as bLAEbSMG ξDM,
where bLAE,bSMG , and ξDM are the large scale bias of
the LAE, the large scale bias of the SMG, and the dark
matter correlation function. If some of the red SMGs are
not at z= 5.7, the CCF amplitude will decrease by a fac-
tor of 1 fc, where fcis a fraction of the red SMGs that
are not at z= 5.7. The large scale amplitude of the ACF
of LAEs is b2
LAEξDM . Because observed amplitude of the
CCF between the LAEs and red SMGs are comparable
to that of the ACF of LAEs, we get
bLAEbSMG ξDM(1 fc) = b2
LAEξDM ,(10)
and
(1 fc) = bLAE
bSMG
.(11)
The large scale bias of LAEs at z= 5.7 is typically
bLAE '4 (Ouchi et al. 2018). The bias of SMGs is ex-
pected to be larger than that of LAEs (bSMG > bLAE ), be-
cause SMGs are thought to be more massive than LAEs.
For example, the large scale bias of SMGs is typically
3 times larger than that of LAEs at z23 (e.g.,
Webb et al. 2003; Gawiser et al. 2007; Weiß et al. 2009;
Ouchi et al. 2010). On the other hand, the effective vol-
ume of our narrow-band data is 200 ×200 ×80 cMpc3.
Only one halo as massive as Mh1013 Mis expected
to exist in this volume, on average (Tinker et al. 2008).
Thus we get the upper limit of the bias of the SMGs as
bSMG < b(Mh= 1013 M)'14. From the lower and
upper limits obtained, 4 < bSMG <14, we expect that
the fraction of the red SMGs at z= 5.7 are 30100 %,
suggesting that 10 40 red SMGs are at z= 5.7. This
is higher than the expectation from the redshift distri-
bution in Donevski et al. (2018, their Figure 7), hint-
ing that large number of the red SMGs are clustering
at z= 5.7. ALMA follow-up observations for these red
SMGs are now being prepared. It is interesting that the
CCF shows strong correlation between the LAEs and the
red SMGs even at the <2000 scale, while the ACF does
not. It indicates that LAE-red SMG pairs can be more
easily found in the <2000 scale than LAE-LAE pairs.
4.4. Star Formation Activity in z57OD and z66OD
To understand star formation activities in z57OD
and z66OD, we investigate spectral energy distribu-
tions (SEDs) of the LAEs of z57OD and z66OD. We
use the images of Subaru/HSC grizyN B816N B921,
UKIRT/WFCAM JHK in the UKIDSS/UDS pro ject
(Lawrence et al. 2007), and Spitzer/IRAC [3.6] and [4.5]
bands in the SPLASH project (P. Capak in prep.). Some
LAEs are detected in the NIR images, and we can con-
strain SEDs of them. Regarding LAEs not detected in
the NIR images, we stack images of these LAEs, and
make subsamples (”non detection stack” subsamples) in
z57OD and z66OD. We also stack images of all LAEs in
z57OD and z66OD (”all stack” subsamples) to investi-
gate averaged properties.
Firstly we run T-PHOT (Merlin et al. 2016) and gen-
erate residual IRAC images where only the LAEs under
analysis are left. As high-resolution prior images in the
T-PHOT run, we use HSC grizyN B stacked images whose
PSFs are 0.
007. Then we visually inspect all of our LAEs
and exclude sources due to the presence of bad residual
features close to the targets that can possibly affect the
photometry. We cut out 1200 ×1200 images of the LAEs
in each band, and generate median-stacked images of the
subsamples in each bands with IRAF task imcombine. We
show the SEDs of the ”all stack” subsamples at z= 5.7
and 6.6 in the left and center panels in Figure 10, respec-
tively.
We generate the model SEDs at z= 5.7 and 6.6 using
BEAGLE (Chevallard & Charlot 2016). In BEAGLE,
we use the combined stellar population and photoioniza-
tion models presented in Gutkin et al. (2016). Stellar
emission is based on an updated version of the popula-
tion synthesis code of Bruzual & Charlot (2003), while
gas emission is computed with the standard photoion-
ization code CLOUDY (Ferland et al. 2013) following
the prescription of Charlot & Longhetti (2001). The
IGM absorption is considered following a model of In-
oue et al. (2014). In BEAGLE we vary the total mass
of stars formed, ISM metallicity (Zneb), ionization pa-
rameter (Uion), star formation history, stellar age, and
V-band attenuation optical depth (τV), while we fix the
dust-to-metal ratio (ξd) to 0.3 (e.g., De Vis et al. 2017),
and adopt the Calzetti et al. (2000) dust extinction curve.
We choose the constant star formation history because
it reproduces SEDs of high redshift LAEs (Ono et al.
2010; Harikane et al. 2018b). The choice of the extinction
Large Scale Structures with Protoclusters at z67 13
Figure 10. Left and center panel: SEDs of the ”all stack” subsamples in z57OD and z66OD. The circles represent the magnitudes in
the stacked images of each subsample. The filled circles are magnitudes used in the SED fittings. We do not use the magnitudes indicated
with the open circles which are affected by the IGM absorption. The dark gray lines with the gray circles show the best-fit model SEDs,
and the light gray regions show the 1σuncertainties of the best-fit model SEDs. Right panel: SFRs of the LAEs in z57OD and z66OD as
functions of the stellar mass. The red and orange diamonds (open squares) are SFRs of the all (non detection) stack subsamples of z57OD
and z66OD, respectively. SFRs of the individual LAEs detected in the NIR images are shown with the red and orange circles for z57OD
and z66OD, respectively. The black line with the circles and the blue lines show results of the star formation main sequence of Salmon
et al. (2015) at z6 and Steinhardt et al. (2014) at z= 4.86.0, respectively. The dashed lines represent extrapolations from the ranges
these studies investigate. The SFRs of the LAEs in z57OD and z66OD are 5 times higher than galaxies in the main sequence.
law does not affect our conclusions, because our SED fit-
tings infer dust-poor populations such as τV= 0.00.1.
We vary the four adjustable parameters of the model in
vast ranges, 2.0<log(Zneb/Z)<0.2 (with a step of
0.1 dex), 3.0<logUion <1.0 (with a step of 0.1 dex),
6.0<log(Age/yr) <9.0 (with a step of 0.1 dex), and
τV= [0,0.05,0.1,0.2,0.4,0.8,1.6,2]. We assume that the
stellar metallicity is the same as the ISM metallicity, with
interpolation of original templates. We fit our observed
SEDs with these model SEDs, and derive stellar masses
and SFRs of the subsamples and individuals. In the ”all
stack” subsample at z= 5.7, we can constrain the stel-
lar mass, SFR, and metallicity. In the other subsamples,
we fix the metallicity to log(Z/Z) = 0.6 that is the
best-fit value of the ”all stack” subsample at z= 5.7,
because we cannot constrain the metallicity due to the
poor signal-to-noise ratio.
In the right panel in Figure 10, we plot the measured
stellar masses and SFRs for the LAEs of z57OD and
z66OD. We compare them with the star formation main
sequence that is determined with field LBGs. All the
subsamples including ”all stack”, ”non detection stack”,
and individual galaxies show SFRs more than 5 times
higher than the main sequence galaxies in the same
stellar masses, indicating that the LAEs in z57OD and
z66OD are actively forming stars.
We then calculate the SFR densities of z57OD and
z66OD, and compare them with the cosmic average (a.k.a
the Madau-Lilly plot). We measure the SFR densities
using observed galaxies located within 1 physical Mpc
(pMpc) from the centers of the overdensities, follow-
ing previous studies (e.g., Clements et al. 2014; Kato
et al. 2016). We find that 16 LAEs and 3 red SMGs
(5 LAEs and 1 red SMG) are within the 1 pMpc-radius
aperture around z57OD (z66OD). For z57OD, we mea-
sure the total SFR density of the observed LAEs and
red SMGS, because the cross correlation signal suggests
that 30 100% of the red SMGs trace the LAE large
scale structures. We assume that the average SFR of
one LAE is 10 Myr1based on the SED fitting
results. We calculate SFRs of the red SMGs from the
850 µm fluxes assuming the redshift of z= 5.7, the dust
temperature of Tdust = 40 K (R´emy-Ruyer et al. 2013;
Faisst et al. 2017), and the emissivity index of β= 1.5
(Chapman et al. 2005). The effect of these assumptions
is not significant on our conclusions. For example, the
Tdust = 10 K or ∆β= 1.5 difference changes the SFR
density only by a factor of <2. With this assumed tem-
perature, the CMB effect is negligible (<5%; da Cunha
et al. 2013). The uncertainty of the SFR density corre-
sponds to the uncertainty of the fraction of the red SMGs
residing at z= 5.7 (30 100%), because the total SFR
is dominated by the SFRs of the red SMGs.
For z66OD, since we do not know whether the SMG
are also at z= 6.6, we calculate the lower limit of the
SFR density considering only the LAEs.
In Figure 11, we plot the measured SFR densities as
a function of the redshift. The SFR density in z57OD
is 10 times higher than the cosmic average (Madau &
Dickinson 2014). We do not obtain a meaningful con-
straint for z66OD. These results indicate that star for-
mation is enhanced at least in z57OD. This active star
formation in the overdense region may be explained by
high inflow rates in the overdense region. Recent obser-
vational studies reveal that there are tight correlations
between the gas accretion rate and star formation rate
(Harikane et al. 2018a; Tacchella et al. 2018; Behroozi
et al. 2018). Enhanced star formation of LAEs in the
overdense region may be due to high inflow rates in over-
densities whose halo is massive. Indeed the halo masses
of z57OD and z66OD are expected to be 410×1011 M
(see Section 4.2), larger than those of LAEs in normal
14 Harikane et al.
Figure 11. SFR densities. The red bar and orange lower limit are
the SFR densities of z57OD and z66OD. The red bar is the sum-
mation of the observed LAEs and red SMGs with the uncertainty
of the fraction of the red SMGs residing at z= 5.7 (30 100%).
The orange lower limit only takes account for the observed LAEs.
Note that we do not include contributions from faint galaxies not
detected in our data. The black curve is the cosmic average of
the SFR density (Madau & Dickinson 2014). The SFR density of
z57OD is more than 10 times higher than the cosmic average.
fields, 1 ×1011 M(Ouchi et al. 2018).
5. Summary
We have obtained 3D maps of the universe in the
200 ×200 ×80 cMpc3volumes each at z= 5.7
and 6.6 based on the spectroscopic sample of 179 LAEs
that accomplishes the >80% completeness down to
log(LLyα/[erg s1]) = 43.0, based on our Keck and Gem-
ini observations and the literature. We compare spatial
distributions of our LAEs with SMGs, investigate the
stellar populations, and compare our LAEs with the nu-
merical simulations. Our major findings are summarized
below.
1. The 3D maps reveal filamentary large-scale struc-
tures extending over 40 cMpc and two remarkable
overdensities made of at least 44 and 12 LAEs at
z= 5.692 (z57OD) and z= 6.585 (z66OD), re-
spectively. z66OD is the most distant overdensity
spectroscopically confirmed to date with >10 spec-
troscopically confirmed galaxies.
2. We have identified similar overdensities to z57OD
and z66OD in the simulations regarding the over-
density significance and the velocity dispersion of
LAEs. The halo masses of the overdensities in
simulations are (4 10) ×1011 M, which will
grow to cluster-scale halos (Mh1014 M) at the
present day, suggesting that z57OD and z66OD are
protoclusters.
3. We have selected 44 red 850 µm-selected SMGs
that are SMGs expected to reside at z'46
based on their red Herschel color, and calculated
the cross correlation functions between the LAEs
and the red SMGs. We have detected 99.97% cross-
correlation signal between z= 5.7 LAEs and the
red SMGs. This significant correlation suggests
that the dust-obscured SMGs are also tracing the
same large scale structures as the LAEs, which are
typically dust-poor star forming galaxies.
4. Stellar population analyses suggest that LAEs in
z57OD and z66OD are actively forming stars with
SFRs 5 times higher than the main sequence at a
fixed stellar mass. Given the significant correlation
between the LAEs and the red SMGs at z= 5.7,
the SFR density in z57OD is 10 times higher than
the cosmic average (a.k.a. the Madau-Lilly plot).
We thank the anonymous referee for a careful reading
and valuable comments that improved the clarity of the
paper. We are grateful to Renyue Cen, Yi-Kuan Chiang,
Tadayuki Kodama, and Ken Mawatari for their useful
comments and discussions.
The Hyper Suprime-Cam (HSC) collaboration includes
the astronomical communities of Japan and Taiwan, and
Princeton University. The HSC instrumentation and
software were developed by the National Astronomical
Observatory of Japan (NAOJ), the Kavli Institute for
the Physics and Mathematics of the Universe (Kavli
IPMU), the University of Tokyo, the High Energy Ac-
celerator Research Organization (KEK), the Academia
Sinica Institute for Astronomy and Astrophysics in Tai-
wan (ASIAA), and Princeton University. Funding was
contributed by the FIRST program from Japanese Cab-
inet Office, the Ministry of Education, Culture, Sports,
Science and Technology (MEXT), the Japan Society for
the Promotion of Science (JSPS), Japan Science and
Technology Agency (JST), the Toray Science Founda-
tion, NAOJ, Kavli IPMU, KEK, ASIAA, and Princeton
University.
This paper makes use of software developed for the
Large Synoptic Survey Telescope. We thank the LSST
Project for making their code available as free software
at http://dm.lsst.org.
This work is based on observations obtained at the
Gemini Observatory processed using the Gemini IRAF
package, which is operated by the Association of Univer-
sities for Research in Astronomy, Inc., under a cooper-
ative agreement with the NSF on behalf of the Gemini
partnership: the National Science Foundation (United
States), the National Research Council (Canada), CON-
ICYT (Chile), Ministerio de Ciencia, Tecnolog´ıa e In-
novaci´on Productiva (Argentina), and Minist´erio da
Ciˆencia, Tecnologia e Inova¸ao (Brazil).
This work is supported by World Premier Inter-
national Research Center Initiative (WPI Initiative),
MEXT, Japan, and KAKENHI (15H02064, 17H01110,
and 17H01114) Grant-in-Aid for Scientific Research (A)
through Japan Society for the Promotion of Science
(JSPS). Y.H. acknowledges support from the Advanced
Leading Graduate Course for Photon Science (ALPS)
grant and the JSPS through the JSPS Research Fellow-
ship for Young Scientists. N.K. acknowledges supports
from the JSPS grant 15H03645. I.R.S. acknowledges
supports from STFC (ST/P000541/1) and the ERC Ad-
vanced Grant DUSTYGAL (321334). M.I. acknowledges
the support from the National Research Foundation of
Large Scale Structures with Protoclusters at z67 15
Korea (NRF) grant, No. 2017R1A3A3001362.
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Large Scale Structures with Protoclusters at z67 17
Table 3
An Overview of High Redshift Protoclusters
Name z Nspec δSample Windowsize dz σVMhRef.
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
Protocluster with Nspec 10
z66OD 6.59 12 14.3±2.1 LAE π×4.220.1 670 ±200 5.4×1014 This work
HSC-z7PCC26 6.54 14 6.8+6.1
3.7LAE π×4.220.1 572 8.4×1014 C17,19,Hi18
SDF 6.01 10 16 ±7 LBG 6 ×60.05 647 ±124 (2 4) ×1014 To12,14
z57OD 5.69 44 11.5±1.6 LAE π×4.220.1 1280 ±220 4.8×1014 O05,J18,This work
SPT2349-56 4.31 14 >1000 SMG π×0.1620.1 408+82
56 1.16 ×1013 M18
TNJ1338-1942 4.11 37 3.7+1.0
0.8LAE/LBG 7 ×7(×2) 0.049 265 ±65 (6 9) ×1014 V02,05,07,M04,Z05,Ov08
DRC-protocluster 4.00 10 5.511.0 SMG 0.61 ×0.730 ... 794 (3.24.4) ×1013 O18
PC217.96+32.3 3.79 65 14 ±7 LAE π×1.220.035 350 ±40 (0.61.3) ×1015 Lee14,D16,S19
D4GD01 3.67 11 ... LBG π×1.821 352 ±140 ... To16
ClJ0227-0421 3.29 19 10.5±2.8 Spec π×6.220.09 995 ±343 (1.93.3) ×1014 Lem14
TNJ2009-3040 3.16 >11 0.7+0.8
0.6LAE 7 ×7 0.049 515 ±90 ... V07
MRC0316-257 3.13 31 2.3+0.5
0.4LAE 7 ×7 0.049 640 ±195 (3 5) ×1014 V05,07
SSA22FLD 3.09 >15 3.6+1.4
1.2LBG/LAE/SMG 11.5×9 0.034 ... (1.01.4) ×1015 S98,00,M05,Y12,U17,18
MRC0943-242 2.92 28 2.2+0.9
0.7LAE 7 ×7 0.056 715 ±105 (4 5) ×1014 V07
P2Q1 2.90 12 12 ±2 Spec 7 ×8 0.016 270 ±80 8.1×1014 C14
MRC0052-241 2.86 37 2.0+0.5
0.4LAE 7 ×7 0.054 980 ±120 (3 4) ×1014 V07
HS1549 2.85 26 5 LBG/SMG ... 0.060 . . . . . . M13,Lac18
PCL1002 2.45 11 10 Spec/LAE/SMG π×2.820.016 426 1014 1015 D15,Ch15,Ca15
HS1700FLD 2.30 19 6.9±2.1 BX/SMG 8 ×8 0.030 ... 1.4×1015 S05,Lac18
PKS1138-262 2.16 15 3 ±2 LAE/HAE/SMG 7 ×7 0.053 900 ±240 (3 4) ×1014 K00,04a,04b,P00,02,V07,K13,Z18
Protocluster with Nspec <10
A2744z8OD 8.38 1 132+66
51 LBG π×0.121... 9×1013 I16,L17
Borg 8 0 4.5 LBG 2.1×2.31. . . > 2×1014 Tr12
BDF 7.04 3 34 LBG ... 1. . . . . . C18
HSC-z7PCC4 6.58 1 9.0+6.5
4.1LAE π×4.220.1 . . . . . . Hi18
CFHQSJ2329-0301 6.43 0 6 LBG 34 ×27 1.0. . . . . . U10
HSC-z6PCC4 5.72 4 9.7+8.5
5.1LAE π×4.220.1 . . . . . . Hi18
HSC-z6PCC5 5.69 2 9.7+8.5
5.1LAE π×4.220.1 . . . . . . Hi18,P18
COSMOSAzTEC03 5.30 4 ... SMG 1 ×1... ... ... C11
TNJ0924-2201 5.19 6 1.5+1.6
1.0LAE/LBG 7 ×7 0.073 305 ±110 (4 9) ×1014 V04,07,Ov06
SDF 4.86 0 2.0+1.0
2.0LAE 10 ×10 0.060 . . . > 3×1014 S03
PClJ1001+0220 4.57 9 3.30 ±0.32 Spec 11 ×11 0.01 1038 ±178 2.5×1014 Lem18
6C0140+326 4.41 0 8 ±5 LAE 10 ×10 0.04 ... (0.82.9) ×1014 K11
D4UD01 3.24 5 ... LBG π×1.621 61 ±105 ... To16
D1UD01 3.13 5 ... LBG π×1.621 235 ±75 ... To16
LABd05 2.7 0 2 LAE 28 ×11 0.165 . . . . . . P08
USS1558-003 2.53 0 ... HAE 7 ×4 0.041 . . . . . . H12
4C23.56 2.48 3 4.3+5.3
2.6HAE/SMG 7 ×4 0.035 . . . . . . T11,Z18
J2143-4423 2.38 0 5.8±2.5 LAE 44 ×44 0.044 . . . . . . P04
4C10.48 2.35 0 11+2
2HAE 2.5×2.5 0.046 . . . . . . H11
Bo¨oetesJ1430+3522 2.3 0 2.7±1.1 LAE π×520.0037 ... 1.51 ×1015 B17
Note. — (1) Object name. (2) Redshift. (3) Number of spectroscopically confirmed galaxies. (4) Galaxy overdensity. (5) Method of sample selection: (LAE)
narrowband LAE, (HAE) narrowband Hαemitter, (LBG) Lyman break galaxy, (BX) ‘BX’ galaxy of Adelberger et al. (2005), (SMG) sub-millimeter galaxy, (Spec)
spectroscopic survey. (6) Approximate field size or the size of the structure used to calculate overdensity in units of arcmin2. (7) Full width redshift uncertainty
associated with the δquoted. (8) Velocity dispersion (where available) in units of km s1. (9) Inferred total halo mass of the overdensity or expected halo mass at
z= 0 in units of M. (10) Reference (B17:B˘adescu et al. 2017, C11:Capak et al. 2011, C14:Cucciati et al. 2014, Ca15:Casey et al. 2015, Ch15:Chiang et al. 2015,
C18:Castellano et al. 2018, C17,19:Chanchaiworawit et al. 2017, 2019, D15:Diener et al. 2015, D16:Dey et al. 2016, H11:Hatch et al. 2011, H12:Hayashi et al. 2012,
Hi18:Higuchi et al. 2018, I16:Ishigaki et al. 2016, J18:Jiang et al. 2018, K00,04a,04b:Kurk et al. 2000, 2004a,b, K11:Kuiper et al. 2011, K13:Koyama et al. 2013,
Lee14:Lee et al. 2014, Lem14:Lemaux et al. 2014, L17:Laporte et al. 2017 Lac18:Lacaille et al. 2018, Lem18:Lemaux et al. 2018 M04:Miley et al. 2004, M05:Matsuda
et al. 2005, M13:Mostardi et al. 2013, M18:Miller et al. 2018, O05:Ouchi et al. 2005, Ov06,08:Overzier et al. 2006, 2008, O18:Oteo et al. 2018, P00,02:Pentericci et al.
2000, 2002, P04:Palunas et al. 2004, P08:Prescott et al. 2008, P18:Pavesi et al. 2018, S98,00,05:Steidel et al. 1998, 2000, 2005, S03:Shimasaku et al. 2003, S19:Shi
et al. 2019, T11:Tanaka et al. 2011, To12,14,16:Toshikawa et al. 2012, 2014, 2016, Tr12:Trenti et al. 2012 U10:Utsumi et al. 2010, U17,18:Umehata et al. 2017, 2018,
V02,04,05,07:Venemans et al. 2002, 2004, 2005, 2007, Y12:Yamada et al. 2012, Z05:Zirm et al. 2005, Z18:Zeballos et al. 2018)
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