The Hyper Suprime-Cam SSP Survey: Overview and Survey Design

TLDR: Hyper Suprime-Cam (HSC) is a wide-field imaging camera on the prime focus of the 8.2m Subaru telescope on the summit of Maunakea in Hawaii as mentioned in this paper.

Abstract: Hyper Suprime-Cam (HSC) is a wide-field imaging camera on the prime focus of the 8.2m Subaru telescope on the summit of Maunakea 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 deg$^2$ in five broad bands ($grizy$), with a $5\,\sigma$ point-source depth of $r \approx 26$. The Deep layer covers a total of 26~deg$^2$ 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 deg$^2$). 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.

Figures

Fig. 4. The blue and dark-green circles show locations of the fiducial pointings of the Deep and UltraDeep fields, respectively (see Table 5). We have an additional five dithered pointings around each fiducial pointing, as described in the text.

Table 1. Hyper Suprime-Cam Characteristics

Table 2. Summary of HSC-Wide, Deep and UltraDeep layers.

Table 3. HSC Filter characteristics. For each filter, we include the effective wavelength, a fractional width defined in equation (2), the FWHM, and a measure of total throughput, as defined in the text. Note that we include the characteristics both of the updated r and i filters (r2 and i2) as well as the old versions used in the early part of the survey.

Fig. 3. The location of the HSC-Wide, Deep, and UltraDeep fields and the AEGIS field on the sky in equatorial coordinates. The color scale gives the level of Galactic dust extinction from Schlegel et al. (1998), as denoted by the color bar. See Figure 4 for the details of the Deep and UltraDeep fields.

Fig. 7. The dithering pattern for one five-dithered pointing in each field of the Deep and UltraDeep layers. The circle has a radius of 0.75◦. The intensity of the color is proportional to the number of visits. The figure

Full text

Publ. Astron. Soc. Japan (2014) 00(0), 1–16
doi: 10.1093/pasj/xxx000
1
The Hyper Suprime-Cam SSP Survey: Overview
and Survey Design
Hiroaki Aihara
1
, Nobuo Arimoto
2,3
, Robert Armstrong
4
,
St
´
ephane Arnouts
5
, Neta A. Bahcall
4
, Steven Bickerton
6
, James Bosch
4
,
Kevin Bundy
7,8
, Peter L. Capak
9
, James H. H. Chan
10,11
, Masashi Chiba
12
,
Jean Coupon
13
, Eiichi Egami
14
, Motohiro Enoki
15
, Francois Finet
3
,
Hiroki Fujimori
16
, Seiji Fujimoto
17
, Hisanori Furusawa
18
,
Junko Furusawa
18
, Tomotsugu Goto
19
, Andy Goulding
4
,
Johnny P. Greco
4
, Jenny E. Greene
4
, James E. Gunn
4
, Takashi Hamana
18
,
Yuichi Harikane
1,17
, Yasuhiro Hashimoto
21
, Takashi Hattori
3
,
Masao Hayashi
18
, Yusuke Hayashi
18
, Krzysztof G. Hełminiak
22
,
Ryo Higuchi
1,17
, Chiaki Hikage
7
, Paul T. P. Ho
10,23
, Bau-Ching Hsieh
10
,
Kuiyun Huang
24
, Song Huang
8,7
, Hiroyuki Ikeda
18
, Masatoshi Imanishi
18,2
,
Akio K. Inoue
25
, Kazushi Iwasawa
26,27
, Ikuru Iwata
3,2
, Anton T. Jaelani
12
,
Hung-Yu Jian
10
, Yukiko Kamata
18
, Hiroshi Karoji
28,4
,
Nobunari Kashikawa
18,2
, Nobuhiko Katayama
7
, Satoshi Kawanomoto
18
,
Issha Kayo
29
, Jin Koda
30
, Michitaro Koike
18
, Takashi Kojima
1,17
,
Yutaka Komiyama
18,2
, Akira Konno
17
, Shintaro Koshida
3
, Yusei Koyama
3,2
,
Haruka Kusakabe
20
, Alexie Leauthaud
7,8
, C.-H. Lee
3
, Lihwai Lin
10
,
Yen-Ting Lin
10
, Robert H. Lupton
4
, Rachel Mandelbaum
31
,
Yoshiki Matsuoka
18,32
, Elinor Medezinski
4
, Sogo Mineo
18
,
Shoken Miyama
33,34
, Hironao Miyatake
35,7
, Satoshi Miyazaki
18,2
,
Rieko Momose
19
, Anupreeta More
7
, Surhud More
7
, Yuki Moritani
7
,
Takashi J. Moriya
18
, Tomoki Morokuma
36,7
, Shiro Mukae
17
,
Ryoma Murata
7,1
, Hitoshi Murayama
7,37,38
, Tohru Nagao
32
,
Fumiaki Nakata
3
, Mana Niida
39
, Hiroko Niikura
1,7
, Atsushi J. Nishizawa
40
,
Yoshiyuki Obuchi
18
, Masamune Oguri
41,7,1
, Yukie Oishi
18
,
Nobuhiro Okabe
42,33,7
, Sakurako Okamoto
43
, Yuki Okura
44,45
,
Yoshiaki Ono
17
, Masato Onodera
3
, Masafusa Onoue
18,2
, Ken Osato
1
,
Masami Ouchi
17,7
, Paul A. Price
4
, Tae-Soo Pyo
3
, Masao Sako
46
, Marcin
Sawicki
47
, Takatoshi Shibuya
17
, Kazuhiro Shimasaku
20,41
,
Atsushi Shimono
7
, Masato Shirasaki
18
, John D. Silverman
7
,
Melanie Simet
48
, Joshua Speagle
49,7
, David N. Spergel
4,50
,
Michael A. Strauss
4,*
, Yuma Sugahara
1,17
, Naoshi Sugiyama
51,7
,
Yasushi Suto
1,41
, Sherry H. Suyu
10,52,53
, Nao Suzuki
7
, Philip J. Tait
3
,
Masahiro Takada
7,*
, Tadafumi Takata
18,2
, Naoyuki Tamura
7
,
Manobu M. Tanaka
54
, Masaomi Tanaka
18
, Masayuki Tanaka
18
,
Yoko Tanaka
3
, Tsuyoshi Terai
3
, Yuichi Terashima
32
, Yoshiki Toba
10
,
Nozomu Tominaga
55,7
, Jun Toshikawa
17
, Edwin L. Turner
4,7,1
,
c
 2014. Astronomical Society of Japan.
arXiv:1704.05858v3 [astro-ph.IM] 15 Mar 2018

2 Publications of the Astronomical Society of Japan, (2014), Vol. 00, No. 0
Tomohisa Uchida
54
, Hisakazu Uchiyama
2
, Keiichi Umetsu
10
,
Fumihiro Uraguchi
18
, Yuji Urata
56
, Tomonori Usuda
18,2
, Yousuke Utsumi
33
,
Shiang-Yu Wang
10
, Wei-Hao Wang
10
, Kenneth C. Wong
18,10
, Kiyoto Yabe
7
,
Yoshihiko Yamada
18
, Hitomi Yamanoi
18
, Naoki Yasuda
7
, Sherry Yeh
3
,
Atsunori Yonehara
57
, Suraphong Yuma
58
1
Department of Physics, University of Tokyo, Tokyo 113-0033, Japan
2
Department of Astronomy, School of Science, Graduate University for Advanced Studies
(SOKENDAI), 2-21-1, Osawa, Mitaka, Tokyo 181-8588, Japan
3
Subaru Telescope, National Astronomical Observatory of Japan, 650 N Aohoku Pl, Hilo, HI
96720
4
Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ 08544
5
CNRS, Laboratoire d’Astrophysique de Marseille, UMR 7326, Aix Marseille Universit,
F-13388, Marseille, France
6
Orbital Insight, 100 W. Evelyn Ave. Mountain View, CA 94041
7
Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI), UTIAS,
University of Tokyo, Chiba 277-8583, Japan
8
Department of Astronomy and Astrophysics, University of California, Santa Cruz, 1156 High
Street, Santa Cruz, CA 95064 USA
9
California Institute of Technology, 1200 E. California Blvd., Pasadena, CA, 91125, USA
10
Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 10617,
Taiwan
11
Department of Physics, National Taiwan University, 10617 Taipei, Taiwan
12
Astronomical Institute, Tohoku University, 6-3, Aramaki, Aoba-ku, Sendai, Miyagi, 980-8578,
Japan
13
Department of Astronomy, University of Geneva, ch. d’
´
Ecogia 16, 1290 Versoix, Switzerland
14
Steward Observatory, University of Arizona, 1540 East Second Street Tucson, AZ
85721-0064, USA
15
Faculty of Business Administration, Tokyo Keizai University, Kokubunji, Tokyo, 185-8502,
Japan
16
MEISEI ELECTRIC CO., LTD, 2223 Naganuma, Isesaki, Gumma, Japan
17
Institute for Cosmic Ray Research, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa,
Chiba 277-8582, Japan
18
National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588,
Japan
19
Institute of Astronomy, National Tsing Hua University, 101, Section 2 Kuang-Fu Road,
Hsinchu, Taiwan, 30013, R.O.C.
20
Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1
Hongo, Bunkyo, Tokyo, 113-0033, Japan
21
Department of Earth Sciences, National Taiwan Normal University No.88, Sec. 4, Tingzhou
Rd., Wenshan District, Taipei 11677, Taiwan
22
Department of Astrophysics, Nicolaus Copernicus Astronomical Center, ul. Rabia
´
nska 8,
87-100 Toru
´
n, Poland
23
East Asian Observatory, 660 N. A’ohoku Place, University Park, Hilo, Hawaii 96720, U.S.A.
24
Department of Mathematics and Science, National Taiwan Normal University, Lin-kou
District, New Taipei City 24449, Taiwan
25
Department of Environmental Science and Technology, Faculty of Design Technology,
Osaka Sangyo University, 3-1-1 Nakagaito, Daito, Osaka 574-8530, Japan
26
Institut de Ci
`
encies del Cosmos (ICCUB), Universitat de Barcelona (IEEC-UB), Mart
´
ı i
Franqu
`
es, 1, 08028 Barcelona, Spain
27
ICREA, Pg. Llu
´
ıs Companys 23, 08010 Barcelona, Spain

Publications of the Astronomical Society of Japan, (2014), Vol. 00, No. 0 3
28
National Institutes of Natural Sciences, 4-3-13 Toranomon, Minato-ku, Tokyo, JAPAN
29
Department of Liberal Arts, Tokyo University of Technology, Ota-ku, Tokyo 144-8650, Japan
30
Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY
11794-3800
31
McWilliams Center for Cosmology, Department of Physics, Carnegie Mellon University,
Pittsburgh, PA 15213, USA
32
Research Center for Space and Cosmic Evolution, Ehime University, 2-5 Bunkyo-cho,
Matsuyama, Ehime 790-8577, Japan
33
Hiroshima Astrophysical Science Center, Hiroshima University, 1-3-1 Kagamiyama,
Higashi-Hiroshima, Hiroshima, 739-8526, Japan
34
Center for Planetary Science, Integrated Research Center of Kobe University, 7-1-48,
Minamimachi, Minatojima, Chuo-ku, Kobe 650-0047, Japan
35
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
36
Institute of Astronomy, University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015,Japan
37
Department of Physics and Center for Japanese Studies, University of California, Berkeley,
CA 94720, USA
38
Theoretical Physics Group, Lawrence Berkeley National Laboratory, MS 50A-5104,
Berkeley, CA 94720
39
Graduate School of Science and Engineering, Ehime University, 2-5 Bunkyo-cho,
Matsuyama, Ehime 790-8577, Japan
40
Institute for Advanced Research, Nagoya University Furocho, Chikusa-ku, Nagoya,
464-8602 Japan
41
Research Center for the Early Universe, University of Tokyo, Tokyo 113-0033, Japan
42
Department of Physical Science, Hiroshima University, 1-3-1 Kagamiyama,
Higashi-Hiroshima, Hiroshima 739-8526, Japan
43
Shanghai Astronomical Observatory, 80 Nandan Rd., Shanghai 200030, China
44
RIKEN High Energy Astrophysics Laboratory, 2-1 Hirosawa, Wako, Saitama 351-0198,
Japan
45
RIKEN BNL Research Center, Bldg. 510A, 20 Pennsylvania Street, Brookhaven National
Laboratory, Upton, NY 11973
46
Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street,
Philadelphia, PA 19104 USA
47
Saint Mary’s University, Department of Astronomy and Physics, 923 Robie Street, Halifax,
NS B3H 3C3, Canada
48
University of California, Riverside, 900 University Avenue, Riverside, CA 92521, USA
49
Harvard University, 60 Garden St., Cambridge, MA 02138, USA
50
Center for Computational Astrophysics, Flatiron Institute, 162 5th Ave. New York, NY 10010
51
Department of Physics and Astrophysics, Nagoya University, Nagoya 464-8602, Japan
52
Max-Planck-Institut f
¨
ur Astrophysik, Karl-Schwarzschild-Str. 1, 85748 Garching, Germany
53
Physik-Department, Technische Universit
¨
at M
¨
unchen, James-Franck-Straße 1, 85748
Garching, Germany
54
Institute of Particle and Nuclear Studies, High Energy Accelerator Research Organization,
203-1 Shirakata, Tokai-mura, Naka-gun, Ibaraki, Japan, 319-1106
55
Department of Physics, Faculty of Science, and Engineering, Konan University, 8-9-1
Okamoto, Kobe, Hyogo 658-8501, Japan
56
Institute of Astronomy, National Central University, Chung-Li 32054, Taiwan
57
Department of Astrophysics and Atmospheric Science, Faculty of Science, Kyoto Sangyo
University, Motoyama, Kamigamo, Kita-ku, Kyoto, 603-8555, JAPAN
58
Department of Physics, Faculty of Science, Mahidol University, Bangkok 10400, Thailand

4 Publications of the Astronomical Society of Japan, (2014), Vol. 00, No. 0
*
Corresponding Authors
∗
E-mail: masahiro.takada@ipmu.jp, strauss@astro.princeton.edu
Received ; Accepted
Abstract
Hyper Suprime-Cam (HSC) is a wide-field imaging camera on the prime focus of the 8.2m
Subaru telescope on the summit of Maunakea 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 deg
2
in five broad bands (grizy), with a 5σ point-source depth of r ≈ 26. The Deep layer
covers a total of 26 deg
2
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 deg
2
). 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.
Key words: TBD
1 Introduction
We live in a golden age for extragalactic astronomy and cosmol-
ogy. We now have a quantitative and highly predictive model for
the overall composition and expansion history of the Universe
that is in accord with a large array of independent and comple-
mentary observations. Observations of galaxies over most of
the 13.8 billion year history of the Universe have led to a broad-
brush understanding of the basics of galaxy evolution. Studies
of the structure of our Milky Way galaxy are in rough agreement
with the current galaxy evolution paradigm. However, there are
fundamental and inter-related questions that remain:
• What is the physical nature of dark matter and dark energy?
Is dark energy truly necessary, or could the accelerated ex-
pansion of the Universe be explained by modifications of the
law of gravity?
• How did galaxies assemble and how did their properties
change over cosmic time? Can a coherent galaxy evolution
model be found that fits both observations of the distant uni-
verse, as well as detailed studies of nearby galaxies including
the Milky Way?
• What is the topology and timing of reionization of the inter-
galactic medium at high redshift? What were the sources of
ultraviolet light responsible for that reionization?
This paper describes a comprehensive deep and wide-angle
imaging survey of the sky designed to address these and other
key questions in astronomy, using the Hyper Suprime-Cam
(HSC), a wide-field imaging camera on the 8.2-meter Subaru
telescope, operated by the National Astronomical Observatory
of Japan (NAOJ) on the summit of Maunakea in Hawaii. The
combination of the large aperture of the Subaru telescope, the
large field of view (1.5 deg diameter) of HSC, and the ex-
cellent image quality of the site and the telescope make this
a powerful instrument for addressing these fundamental ques-
tions in modern cosmology and astronomy. Under the Subaru
Strategic Program (SSP), we began a survey using both broad-
and narrow-band filters in March 2014. The HSC-SSP will use
300 nights of Subaru time over about six years. The survey
consists of three layers of different solid angles, going to differ-
ent depths. With both the broad- and narrow-band photometric
data, we will explore galaxy evolution over the full range of
cosmic history from the present to redshift 7. The measurement
of galaxy shapes in the broad-band images will map the large-
scale distribution and evolution of dark matter through weak
gravitational lensing (WL), and allow us to relate it to galaxy
properties and distribution. Cross-correlations of HSC WL ob-
servables with the spectroscopic galaxy distribution in the Sloan
Digital Sky Survey (SDSS; York et al. 2000)/Baryon Oscillation
Spectroscopic Survey (BOSS; Dawson et al. 2013) and the ob-
served temperature and polarization fluctuations in the Cosmic
Microwave Background (CMB) will constrain the parameters of
the standard model of cosmology, and test for exotic variations
such as deviations from the predictions of General Relativity
on cosmological scales (see Weinberg et al. 2013 for a review).
Studies of the highest-redshift galaxies and quasars discovered
in this survey will lead to a deeper understanding of reioniza-
tion, a key event in the thermal history of the Universe.
The HSC survey follows a long tradition of major imaging
surveys in astronomy. In the modern era, the Sloan Digital Sky
Survey (SDSS; York et al. 2000) imaged one third of the celes-

Publications of the Astronomical Society of Japan, (2014), Vol. 00, No. 0 5
tial sphere with CCDs in five broad bands (ugriz), going to a
depth of r ≈ 22.5. The next generation of imaging surveys has
surpassed SDSS in various combinations of depth, solid angle
coverage, and image quality. For example, the Pan-STARRS1
survey (Chambers et al. 2016) used a 1.8-meter telescope to
cover three-quarters of the sky in grizy almost a magnitude
fainter than SDSS. DECaLS (Blum et al. 2016) is covering
14,000 deg
2
in grz, going somewhat deeper than Pan-STARRS,
and is designed to support the Dark Energy Spectroscopic
Instrument (DESI, DESI Collaboration et al. 2016). The Dark
Energy Survey (Dark Energy Survey Collaboration et al. 2016)
is imaging 5,000 deg
2
of the southern sky in five bands with
the Blanco 4-meter telescope, going to r ≈ 24.3 (10 σ). Weak
lensing cosmology is a key driver of DES, and similarly is a
driver of many of the more recent surveys. For example, the
CFHT Lens Survey (Heymans et al. 2012) covers 154 deg
2
in
five bands, to i
0
= 25.5. The Kilo-Degree Survey (KiDS; de
Jong et al. 2017) is covering 1,500 deg
2
in 4 bands to r = 24.9.
The HSC survey described in this paper goes deeper than all
these surveys, while still covering well over 1,000 deg
2
, and
including a narrow-band imaging component as well.
This is the first paper in a series describing the HSC sur-
vey and its science in a special issue of the Publications of
the Astronomical Society of Japan. Other key papers in this
issue include a technical description of the HSC instrument it-
self (Miyazaki et al. 2017) and the software pipelines that an-
alyze the data (Bosch et al. 2017; Huang et al. 2017, Murata
et al. 2017). The first year of the data covering over 100 deg
2
in five broad bands have been released to the public, including
fully reduced and calibrated images as well as catalogs of de-
tected objects. The data release is described in Aihara et al.
(2017) (hereafter the HSC DR1 paper). A separate analysis and
catalog of galaxy shapes, crucial for weak lensing analysis, is
included in Mandelbaum et al. (2017). This special issue also
includes more than two dozen science papers based on the early
data from the HSC survey, on topics ranging from asteroids to
dwarf companions of the Milky Way, to weak lensing measure-
ments of clusters, to some of the highest redshift quasars known.
We summarize the characteristics of the HSC instrument it-
self in § 2. The survey design is described in § 3, and the ob-
serving strategy follows in § 3.2 and § 3.3. § 4 gives a brief
overview of the data processing. We summarize, with a view to
the future, in § 5.
2 Hyper Suprime-Cam
While there are other 8-meter class telescopes around the world,
Subaru is the one with by far the largest field of view. Suprime-
Cam (Miyazaki et al. 2002), with its ∼ 0.25 deg
2
field of view
and superb delivered image quality (routinely 0.6
00
FWHM),
has been a world leader in wide-field studies of the distant
0
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114
115
Science CCDs
Focusing CCDs
Auto guider CCDs
Fig. 1. The layout of 116 CCD chips, each of which has 2048×4096 pixels
(5.73
0
× 11.47
0
), on the focal plane. The CCD chips are arranged with two
different gaps of approximately 12
00
and 53
00
between the neighboring
chips. The focal plane is approximately 1.5
◦
in diameter. There are 104
science chips (indicated in blue), 4 chips used for auto-guiding (in yellow)
and 8 chips for monitoring the focus (in light red). Each chip is identified
with a number from 0 to 115.
Fig. 2. The HSC bandpasses, including the reflectivity of all mirrors,
transmission of all optics and filters as well as the atmosphere, and
response of the CCDs, assuming an airmass of 1.2. Both the broad-band
and narrow-band filters used in the survey are shown. The lower panel
shows the spectrum of sky emission lines, demonstrating that the red
narrow-band filters lie in relatively dark regions of the sky spectrum.

Frequently asked questions

Q1. What contributions have the authors mentioned in the paper "The hyper suprime-cam ssp survey: overview and survey design" ?

Here the authors 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. 

Q2. What future works have the authors mentioned in the paper "The hyper suprime-cam ssp survey: overview and survey design" ?

With it, the authors plan to carry out wide-field spectroscopic surveys of stars, galaxies, and quasars selected from the superb imaging data from the HSC-SSP survey. 

Q3. What is the next generation of imaging surveys?

The next generation of imaging surveys has surpassed SDSS in various combinations of depth, solid angle coverage, and image quality. 

Q4. How many visits are there in the UltraDeep layer?

In the UltraDeep layer, the exposure time for each visit is 300 seconds for all bands, and the authors carry out 3-10 visits on a given night. 

Q5. What are the primary goals of the HSC-Deep and UltraDeep layers?

The primary science goals of the HSC-Deep and UltraDeep layers are the study of galaxy and AGN evolution over cosmic time, and a survey for high-redshift supernovae as a cosmological probe. 

Q6. How many filters can be used in a run?

On any given run, the filter exchanger typically holds four or all five of the broad-band filters, and one or two of the narrow-band filters. 

Q7. What is the dither pattern used to offset the telescope between exposures?

The authors offset the telescope between successive exposures with a dither pattern parameterized by (∆rdith, θdith), where ∆rdith is the angular separation between the centers of the fiducial pointing and the dithered pointings, and θdith is the position angle from the west-east direction on the sky. 

Q8. How long does it take to change the filters?

for safety reasons the primary mirror cover needs to be closed and instrument rotated to a fiducial angle before the filters can be changed, meaning that it takes about 30 minutes in practice between the end of one sky exposure and the start of the following exposure in a different filter. 

Q9. Why is the filter exchanger installed on the day after the instrument is installed?

because the filter exchanger is installed the day after the instrument is installed, and removed the day before the instrument is removed, only one filter is available for observations on the first and last day of any given run. 

Q10. How long have the authors been observing in the wide layer?

In the first years of the HSC SSP survey, the authors have aimed to reach full depth in any given region of the Wide layer in all five filters fairly quickly (i.e., within a few lunations), and only then build up area with time. 

Q11. Why do the authors use the Wide layer?

Because the Deep and UltraDeep fields are quite small (relatively speaking), the authors cannot take as large a dither as the authors do in the Wide layer. 

Q12. What is the filter set used for the HSC survey?

The HSC survey uses five broad-band filters (grizy) modeled on the SDSS filter set (Figure 2 and Table 3), as well as four narrow-band filters sensitive to emission lines such as theLyman-α line over a wide range of redshifts. 

Q13. What is the average time spent in the Wide layer?

Their survey design includes about 2/3 of the observing time in the Wide layer, with 1/3 for the Deep and UltraDeep observations combined. 

Q14. What is the purpose of the survey?

As the survey matures, the authors are working to bridge already-observed fields in order to maximize the contiguous area in the survey footprint. 

Q15. What is the dither pattern for the j-th visit exposure?

The authors take θdith =θ0 +(2π/Ndith)×j for the position angle for the j-th visit exposure; j = 0,1,2 or j = 0,1, · · · ,4 for the gr or izy filters, respectively. 

Q16. How many i-bands are used in the WL analysis?

At a depth of i≈ 26, the authors predict a weighted mean number density of galaxies for which shapes can be measured of n̄eff ' 20 arcmin−2, with a mean redshift of 〈z〉 ' 1. Combining the i-band data with the grzy photometry will allow us to estimate photometric redshifts (photo-z) for every galaxy used in the WL analysis; the relative depths of the different bands are selected to optimize the photoz accuracy (Tanaka et al. 2017). 

Q17. What is the pointing strategy for the UltraDeep broad-band survey?

The gray circles are the “fiducial” pointings which define the survey geometry, each with a radius of 0.75◦, approximately denoting the HSC field-of-view. 

Q18. What is the difference between Deep and UltraDeep?

The Deep and UltraDeep data will have significantly higher signal-to-noise ratio for galaxies at the limits of the Wide layer imaging, making them ideal for testing systematics in shape and photometric measurements (see Table 4). 

Q19. What is the cadence for the UltraDeep broad-band observations?

Starting in late 2016, the authors adopted a specific cadence for the UltraDeep broad-band observations to maximize the sensitivity to and measurement of the lightcurves of z >∼ 1 supernovae. 

Q20. How do the authors adjust the focus when the instrument is out of focus?

When they show the instrument to be out of focus, the authors take a special set of short exposures over a range of focus positions, and adjust the focus accordingly.