The Dark Energy Survey: Data Release 1
T. M. C. Abbott
1
, F. B. Abdalla
2,3
, S. Allam
4
, A. Amara
5
, J. Annis
4
, J. Asorey
6,7,8
, S. Avila
9,10
, O. Ballester
11
, M. Banerji
12,13
,
W. Barkhouse
14
, L. Baruah
15
, M. Baumer
16,17,18
, K. Bechtol
19
, M. R. Becker
16,17
, A. Benoit-Lévy
2,20,21
, G. M. Bernstein
22
,
E. Bertin
20,21
, J. Blazek
23,24
, S. Bocquet
25
, D. Brooks
2
, D. Brout
22
, E. Buckley-Geer
4
, D. L. Burke
17,18
, V. Busti
26,27
,
R. Campisano
26
, L. Cardiel-Sas
11
, A. Carnero Rosell
26,28
, M. Carrasco Kind
29,30
, J. Carretero
11
, F. J. Castander
31,32
,
R. Cawthon
33
, C. Chang
33
, X. Chen
34
, C. Conselice
35
, G. Costa
26
, M. Crocce
31,32
, C. E. Cunha
17
,C.B.D’Andrea
22
,
L. N. da Costa
26,28
, R. Das
34
, G. Daues
29
, T. M. Davis
7,8
, C. Davis
17
, J. De Vicente
36
, D. L. DePoy
37
, J. DeRose
16,17
, S. Desai
38
,
H. T. Diehl
4
, J. P. Dietrich
39,40
, S. Dodelson
41
, P. Doel
2
, A. Drlica-Wagner
4
,T.F.Eifler
42,43
, A. E. Elliott
44
, A. E. Evrard
34,45
,
A. Farahi
34
, A. Fausti Neto
26
, E. Fernandez
11
, D. A. Finley
4
, B. Flaugher
4
, R. J. Foley
46
, P. Fosalba
31,32
, D. N. Friedel
29
,
J. Frieman
4,33
, J. García-Bellido
10
, E. Gaztanaga
31,32
, D. W. Gerdes
34,45
, T. Giannantonio
12,13,47
, M. S. S. Gill
16,17,18
,
K. Glazebrook
6
, D. A. Goldstein
48,49
, M. Gower
29
, D. Gruen
17,18
, R. A. Gruendl
29,30
, J. Gschwend
26,28
, R. R. Gupta
25,48
,
G. Gutierrez
4
, S. Hamilton
34
, W. G. Hartley
2,5
, S. R. Hinton
7
, J. M. Hislop
15
, D. Hollowood
50
, K. Honscheid
23,44
,
B. Hoyle
47,51
, D. Huterer
34
, B. Jain
22
, D. J. James
52
, T. Jeltema
50
, M. W. G. Johnson
29
, M. D. Johnson
29
, T. Kacprzak
5
, S. Kent
4,33
,
G. Khullar
33
, M. Klein
40,51
, A. Kovacs
11
, A. M. G. Koziol
29
, E. Krause
42,43
, A. Kremin
34
, R. Kron
4,53
, K. Kuehn
54
,
S. Kuhlmann
25
, N. Kuropatkin
4
, O. Lahav
2
, J. Lasker
33,53
,T.S.Li
4
,R.T.Li
29
, A. R. Liddle
55
, M. Lima
26,27
, H. Lin
4
,
P. López-Reyes
36
, N. MacCrann
23,44
, M. A. G. Maia
26,28
, J. D. Maloney
29
, M. Manera
11,74
, M. March
22
, J. Marriner
4
,
J. L. Marshall
37
, P. Martini
23,56
, T. McClintock
57
, T. McKay
34
, R. G. McMahon
12,13
, P. Melchior
58
, F. Menanteau
29,30
,
C. J. Miller
34,45
, R. Miquel
11,59
, J. J. Mohr
39,40,51
, E. Morganson
29
, J. Mould
6
, E. Neilsen
4
, R. C. Nichol
9
, F. Nogueira
26
,
B. Nord
4
, P. Nugent
48
, L. Nunes
26
, R. L. C. Ogando
26,28
, L. Old
35,60
, A. B. Pace
37
, A. Palmese
2
, F. Paz-Chinchón
29
,
H. V. Peiris
2
, W. J. Percival
9
, D. Petravick
29
, A. A. Plazas
43
, J. Poh
33
, C. Pond
29
, A. Porredon
31,32
, A. Pujol
31,32
, A. Refregier
5
,
K. Reil
18
, P. M. Ricker
29,30
, R. P. Rollins
61
, A. K. Romer
15
, A. Roodman
17,18
, P. Rooney
15
, A. J. Ross
23
, E. S. Rykoff
17,18
,
M. Sako
22
, M. L. Sanchez
26
, E. Sanchez
36
, B. Santiago
26,62
, A. Saro
40,63
, V. Scarpine
4
, D. Scolnic
33
, S. Serrano
31,32
,
I. Sevilla-Noarbe
36
, E. Sheldon
64
, N. Shipp
33
, M. L. Silveira
26
, M. Smith
65
, R. C. Smith
1
, J. A. Smith
66
,
M. Soares-Santos
4,67
, F. Sobreira
26,68
, J. Song
69
, A. Stebbins
4
, E. Suchyta
70
, M. Sullivan
65
, M. E. C. Swanson
29
,
G. Tarle
34
, J. Thaler
71
, D. Thomas
9
, R. C. Thomas
48
, M. A. Troxel
23,44
, D. L. Tucker
4
, V. Vikram
25
, A. K. Vivas
1
,
A. R. Walker
1
, R. H. Wechsler
16,17,18
, J. Weller
39,47,51
, W. Wester
4
, R. C. Wolf
22
,H.Wu
44
, B. Yanny
4
, A. Zenteno
1
,
Y. Zhang
4
, J. Zuntz
55
(DES Collaboration),
and
S. Juneau
72
, M. Fitzpatrick
72
, R. Nikutta
72
, D. Nidever
72,73
, K. Olsen
72
, and A. Scott
72
(NOAO Data Lab)
1
Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, Casilla 603, La Serena, Chile
2
Department of Physics & Astronomy, University College London, Gower Street, London, WC1E 6BT, UK
3
Department of Physics and Electronics, Rhodes University, P.O. Box 94, Grahamstown, 6140, South Africa
4
Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, IL 60510, USA
5
Department of Physics, ETH Zurich, Wolfgang-Pauli-Strasse 16, CH-8093 Zurich, Switzerland
6
Centre for Astrophysics & Supercomputing, Swinburne University of Technology, Victoria 3122, Australia
7
School of Mathematics and Physics, University of Queensland, Brisbane, QLD 4072, Australia
8
ARC Centre of Excellence for All-sky Astrophysics (CAASTRO)
9
Institute of Cosmology & Gravitation, University of Portsmouth, Portsmouth, PO1 3FX, UK
10
Instituto de Fisica Teorica UAM/CSIC, Universidad Autonoma de Madrid, E-28049 Madrid, Spain
11
Institut de Física d’Altes Energies (IFAE), The Barcelona Institute of Science and Technology, Campus UAB, E-08193 Bellaterra (Barcelona) Spain
12
Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
13
Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
14
University of North Dakota, Department of Physics and Astrophysics, Witmer Hall, Grand Forks, ND 58202, USA
15
Department of Physics and Astronomy, Pevensey Building, University of Sussex, Brighton, BN1 9QH, UK
16
Department of Physics, Stanford University, 382 Via Pueblo Mall, Stanford, CA 94305, USA
17
Kavli Institute for Particle Astrophysics & Cosmology, P.O. Box 2450, Stanford University, Stanford, CA 94305, USA
18
SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
19
LSST, 933 North Cherry Avenue, Tucson, AZ 85721, USA; kbechtol@lsst.org
20
Sorbonne Universités, UPMC Univ Paris 06, UMR 7095, Institut d’Astrophysique de Paris, F-75014, Paris, France
21
CNRS, UMR 7095, Institut d’Astrophysique de Paris, F-75014, Paris, France
22
Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104, USA
23
Center for Cosmology and Astro-Particle Physics, The Ohio State University, Columbus, OH 43210, USA
24
Institute of Physics, Laboratory of Astrophysics, École Polytechnique Fédérale de Lausanne (EPFL), Observatoire de Sauverny, 1290 Versoix, Switzerland
25
Argonne National Laboratory, 9700 South Cass Avenue, Lemont, IL 60439, USA
26
Laboratório Interinstitucional de e-Astronomia—LIneA, Rua Gal. José Cristino 77, Rio de Janeiro, RJ—20921-400, Brazil
27
Departamento de Física Matemática, Instituto de Física, Universidade de São Paulo, CP 66318, São Paulo, SP, 05314-970, Brazil
28
Observatório Nacional, Rua Gal. José Cristino 77, Rio de Janeiro, RJ—20921-400, Brazil
29
National Center for Supercomputing Applications, 1205 West Clark St., Urbana, IL 61801, USA; mcarras2@illinois.edu
30
Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 W. Green Street, Urbana, IL 61801, USA
The Astrophysical Journal Supplement Series, 239:18 (25pp), 2018 December https://doi.org/10.3847/1538-4365/aae9f0
© 2018. The American Astronomical Society. All rights reserved.
1
31
Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Can Magrans, s/n, E-08193 Barcelona, Spain
32
Institut d’Estudis Espacials de Catalunya (IEEC), E-08193 Barcelona, Spain
33
Kavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637, USA
34
Department of Physics, University of Michigan, Ann Arbor, MI 48109, USA
35
University of Nottingham, School of Physics and Astronomy, Nottingham NG7 2RD, UK
36
Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), Madrid, Spain; nsevilla@gmail.com
37
George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, and Department of Physics and Astronomy, Texas A&M University,
College Station, TX 77843, USA
38
Department of Physics, IIT Hyderabad, Kandi, Telangana 502285, India
39
Excellence Cluster Universe, Boltzmannstr. 2, D-85748 Garching, Germany
40
Faculty of Physics, Ludwig-Maximilians-Universität, Scheinerstr. 1, D-81679 Munich, Germany
41
Observatories of the Carnegie Institution of Washington, 813 Santa Barbara St., Pasadena, CA 91101, USA
42
Department of Astronomy/Steward Observatory, 933 North Cherry Avenue, Tucson, AZ 85721-0065, USA
43
Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109, USA
44
Department of Physics, The Ohio State University, Columbus, OH 43210, USA
45
Department of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA
46
Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA
47
Universitäts-Sternwarte, Fakultät für Physik, Ludwig-Maximilians Universität München, Scheinerstr. 1, D-81679 München, Germany
48
Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA
49
Department of Astronomy, University of California, Berkeley, 501 Campbell Hall, Berkeley, CA 94720, USA
50
Santa Cruz Institute for Particle Physics, Santa Cruz, CA 95064, USA
51
Max Planck Institute for Extraterrestrial Physics, Giessenbachstrasse, D-85748 Garching, Germany
52
Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
53
Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL 60637, USA
54
Australian Astronomical Observatory, North Ryde, NSW 2113, Australia
55
Institute for Astronomy, University of Edinburgh, Edinburgh EH9 3HJ, UK
56
Department of Astronomy, The Ohio State University, Columbus, OH 43210, USA
57
Department of Physics, University of Arizona, Tucson, AZ 85721, USA
58
Department of Astrophysical Sciences, Princeton University, Peyton Hall, Princeton, NJ 08544, USA
59
Institució Catalana de Recerca i Estudis Avançats, E-08010 Barcelona, Spain
60
Department of Astronomy & Astrophysics, University of Toronto, Toronto, ON M5S 2H4, Canada
61
Jodrell Bank Center for Astrophysics, School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, M13 9PL, UK
62
Instituto de Física, UFRGS, Caixa Postal 15051, Porto Alegre, RS—91501-970, Brazil
63
INAF-Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, I-34131, Trieste, Italy
64
Brookhaven National Laboratory, Bldg. 510, Upton, NY 11973, USA
65
School of Physics and Astronomy, University of Southampton, Southampton, SO17 1BJ, UK
66
Austin Peay State University, Dept. Physics-Astronomy, P.O. Box 4608 Clarksville, TN 37044, USA
67
Department of Physics, Brandeis University, Waltham, MA 02453, USA
68
Instituto de Física Gleb Wataghin, Universidade Estadual de Campinas, 13083-859, Campinas, SP, Brazil
69
Korea Astronomy and Space Science Institute, Yuseong-gu, Daejeon, 305-348, Republic of Korea
70
Computer Science and Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
71
Department of Physics, University of Illinois at Urbana-Champaign, 1110 W. Green St., Urbana, IL 61801, USA
72
National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 8571, USA
73
Department of Physics, Montana State University, P.O. Box 173840, Bozeman, MT 59717-3840, USA
Received 2018 January 17; revised 2018 September 20; accepted 2018 October 19; published 2018 November 26
Abstract
We describe the first public data release of the Dark Energy Survey, DES DR1, consisting of reduced single-epoch
images, co-added images, co-added source catalogs, and associated products and services assembled over the first 3 yr
of DES science operations. DES DR1 is based on optical/near-infrared imaging from 345 distinct nights (2013 August
to 2016 February) by the Dark Energy Camera mounted on the 4 m Blanco telescope at the Cerro Tololo Inter-
American Observatory in Chile. We release data from the DES wide-area survey covering ∼5000 deg
2
of the southern
Galactic cap in five broad photometric bands, grizY. DES DR1 has a median delivered point-spread function of
=g 1.1
2
, r=0.96, i=0.88, z=0.84, and Y=0 90 FWHM, a photometric precision of <1% in all bands, and an
astrometric precision of 151
mas
. The median co-added catalog depth for a 1 95 diameter aperture at signal-to-noise
ratio (S/N)=10 is g=24. 33, r=24.08, i=23.44, z=22.69, and Y=21.44
mag
.DESDR1includesnearly400
million distinct astronomical objects detected in ∼10,000 co-add tiles of size 0.534 deg
2
produced from ∼39,000
individual exposures. Benchmark galaxy and stellar samples contain ∼310 million and ∼80 million objects,
respectively, following a basic object quality selection. These data are accessible through a range of interfaces, including
query web clients, image cutout servers, jupyter notebooks, and an interactive co-add image visualization tool. DES
DR1 constitutes the largest photometric data set to date at the achieved depth and photometric precision.
Key words: astronomical databases: miscellaneous – catalogs – cosmology: observations – surveys – techniques:
image processing – techniques: photometric
1. Introduction
Advances in telescope construction, sensor technology, and
data processing have allowed us to map the sky with increasing
speed and precision, enabling discovery through statistical
74
Visitor at Kavli Institute for Cosmology, University of Cambridge,
Madingley Road, Cambridge CB3 0HA.
2
The Astrophysical Journal Supplement Series, 239:18 (25pp), 2018 December Abbott et al.
analysis of astronomical source populations, as well as the
detection of rare and/or unexpected objects (Tyson 2010). The
Dark Energy Survey (DES) is one of several ground-based
wide-area optical and near-IR imaging surveys, including the
Sloan Digital Sky Survey (SDSS; York et al. 2000), the
Panoramic Survey Telescope and Rapid Response System 1
(Pan-STARRS1 or PS1; Kaiser et al. 2010), the Kilo Degree
Survey (KiDS; de Jong et al. 2013), the Hyper Suprime-Cam
Subaru Strategic Program (HSC-SSP; Aihara et al. 2018a), and
the future Large Synoptic Survey Telescope (LSST; Ivezic
et al. 2008).
The instrumental and observational strategies of DES are
designed to improve our understanding of cosmic acceleration
and the nature of dark energy using four complementary
methods: weak gravitational lensing, galaxy cluster counts, the
large-scale clustering of galaxies (including baryon acoustic
oscillations), and the distances to Type Ia supernovae (SNe;
DES Collaboration 2005). To achieve these goals, DES conducts
two distinct multiband imaging surveys: a ∼5000 deg
2
wide-
area survey in the grizY bands and a ∼27 deg
2
deep SN survey
observed in the griz bands with a ∼7-day cadence (Diehl et al.
2014; Kessler et al. 2015).
DES uses the Dark Energy Camera (DECam; Honscheid
et al. 2008; Flaugher et al. 2015), a 570 MP camera with a
3 deg
2
field of view installed at the prime focus of the Blanco 4
m telescope at the Cerro Tololo Inter-American Observatory
(CTIO) in northern Chile. Survey observations comprise ∼105
equivalent full nights per year (August through mid-February),
including full and half nights. Each exposure is delivered from
CTIO to the National Center for Supercomputing Applications
(NCSA) at the University of Illinois at Urbana-Champaign for
processing generally within minutes of being observed. At
NCSA, the DES Data Management system (DESDM; Sevilla
et al. 2011; Desai et al. 2012; Mohr et al. 2012; Morganson
et al. 2018) generates a variety of scientific products, including
single-epoch and co-added images with associated source
catalogs of suitable quality to perform precise cosmological
measurements (e.g., DES Collaboration 2017).
Raw DES exposures become publicly available 1 yr after
acquisition from the National Optical Astronomy Observatory
(NOAO) Science Archive,
75
and DES is scheduled to provide
two major public releases of processed data. The first DES Data
Release (DR1), described here, encompasses data products
derived from wide-area survey observations taken in the first 3
yr of science operations (Y1 –Y3, from 2013 August to 2016
February). A second major data release (DR2) is scheduled for
after DES is completed. In addition to DR1 and DR2, the DES
Collaboration prepares incremental internal releases with
value-added products and detailed characterizations of survey
performance that are designed to support cosmological
analyses (e.g., Y1 Gold; Drlica-Wagner et al. 2018). A subset
of these products associated with data collected during the DES
Science Verification (SV) period (2012 November 1 through
2013 February 22) was released in 2016 January.
76
In 2018
September, the value-added products from a number of selected
DES publications corresponding to Y1 data were released
as well.
77
Additional releases of value-added data products are
expected to support future scientific publications.
In this work, we present the content, validation, and data
access services for DES DR1. DR1 is composed of co-added
images and catalogs, as well as calibrated single-epoch images,
from the processing of the first 3 yr of DES wide-area survey
observations. Access to DES DR1 data is provided via web
interfaces and auxiliary tools, which is made possible through
the partnership between NCSA,
78
LIneA,
79
and NOAO,
80
at
the following URL:https://des.ncsa.illinois.edu/releases/dr1.
In Section 2, we briefly describe the DECam instrument and the
DES observation strategy for the wide-field survey (the data set
included in this release). Section 3 includes an overview of how
the raw data were processed by DESDM at NCSA and served
as the catalogs and images made available in this release. A
basic quality evaluation of these products is presented in
Section 4, followed by a description of products as they appear
in the DR1 release (Section 5). Section 6 describes the various
data access frameworks and tools made available for DR1. A
summary of the release and information on expected future
releases are given in Section 7. We direct the reader to
Appendix A for definitions of terms and acronyms used
throughout the text.
Except where noted, all magnitudes quoted in the text are in
the AB system (Oke 1974).
2. Data Acquisition
DR1 is composed of data taken on 345 distinct nights spread
over the first 3 yr of DES operations from 2013 August 15 to
2016 February 12.
81
In this section, we briefly describe the
characteristics of the DECam instrument and the DES
observation strategy to provide context for DR1. We point
the reader to other DES publications for further details on the
technical aspects summarized here (i.e., Diehl et al. 2016;
Drlica-Wagner et al. 2018; Morganson et al. 2018).
Figure 1. DR1 standard bandpasses for the DECam grizY filters. The
bandpasses represent the total system throughput, including atmospheric
transmission (air mass=1.2) and the average instrumental response across the
science CCDs (Section 5.4).
75
http://archive.noao.edu/
76
https://des.ncsa.illinois.edu/releases/sva1
77
https://des.ncsa.illinois.edu/releases/y1a1
78
National Center for Supercomputing Applications.
79
Laboratório Interinstitucional de e-Astronomia.
80
National Optical Astronomy Observatory.
81
DES was scheduled for 319 equivalent full nights, including half nights,
during this period (Diehl et al. 2016).
3
The Astrophysical Journal Supplement Series, 239:18 (25pp), 2018 December Abbott et al.
2.1. DECam
DECam is a wide-field-of-view (3 deg
2
) mosaic camera
containing 62 science CCDs (Flaugher et al. 2015).
82
The
corrector system and pixel size provide an average plate scale
of 0
263 per pixel. The DES wide-area survey observes five
broadband filters, grizY (Figure 1 ), and the standard bandpasses
for these filters are included as part of DR1 (Section 5.4) . The
DES filters are very similar to their analogously named
counterparts from other surveys.
Uniquely, the DES z band has greater sensitivity at longer
wavelengths than the SDSS z band and overlaps with the DES
Y band. Additional details, including construction, installation,
and a description of DECam subsystems and interfaces, are
provided in Flaugher et al. (2015).
2.2. Survey Operations
The target footprint of the DES wide-area and SN surveys
are shown in Figure 2. All R.A., decl. coordinates in this paper
refer to the J2000 epoch. The wide-area footprint shape was
selected to obtain a large overlap with the South Pole Telescope
survey (Carlstrom et al. 2011) and Stripe 82 from SDSS
(Abazajian et al. 2009) and includes a connection region to
enhance overall calibration. Given the cosmological goals of
the survey, DES avoids the Galactic plane to minimize stellar
foregrounds and extinction from interstellar dust.
The wide-field survey uses exposure times of 90
s
for griz and
45
s
for Y band, yielding a typical single-epoch point-sprea d func-
tion (PSF) depth at signal-to-noise ratio (S/N)=10 of g=23.57,
r=23.34, i=22.78, z=22.10, and Y=20.69 (Morganson
et al. 2018). The completed survey is expected to be roughly 1 mag
deeper, through the co-addition of 10 images in each of the bands
for a cumulative exposure time of 900
s
in griz and 450
s
in Y.
83
Nightly observations are divided between the wide-field and
SN surveys based on current environmental conditions and the
data quality assessments of previous observations. Real-time
optimization of survey strategy is accomplished through the
ObsTac software on the mountain (Neilsen & Annis 2014).
ObsTac selects grizY exposures accounting for moon position,
sky brightness, current seeing, air mass, hour angle, and other
observational characteristics. DES exposures are offset by
roughly half the focal plane radius on average in successive
visits to the same field, or “hex,” such that objects are observed
by different CCDs in each “tiling.” This observing strategy
minimizes inhomogeneities from the DECam geometry and
enhances the relative photometric calibration. Blanco is an
equatorial mount telescope, and there is no rotation between
dithered and/or repeated exposures.
A single raw DECam exposure is ∼0.5
GB
in size
(compressed), and DES collects ∼300 science exposures per
night, depending on the season, survey strategy, and SN field
schedule. These data are transferred to NOAO for archiving
(Fitzpatrick 2010; Honscheid et al. 2012) and to NCSA for
further evaluation and processing by the DESDM system; a
summary is provided in Section 3. These raw single-epoch
images are made available by NOAO and are accessible as
described in Section 6.
2.3. Survey Progress through DR1
Between Y1 and Y3, 38,850 wide-field exposures passed
baseline survey-quality thresholds based on effective exposure
time and PSF FWHM (Morganson et al. 2018, Section 4.7) and
are included in co-add processing by DESDM (Morganson
et al. 2018). The median air mass of DR1 survey-quality
exposures was 1.22, with >99% of exposures taken at air
mass <1.4. Meanwhile, the median delivered seeing (FWHM)
was g=1.12, r=0.96, i=0.88, z =0.84, and
=
Y
0. 90
(Figure 3). Note that ObsTac prioritizes observations in the riz
bands during periods of good seeing to advance the main
science goals of DES (e.g., cosmological constraints from weak
gravitational lensing). Figure 4 shows the distribution of sky
Figure 2. Plot of the DES survey area in celestial coordinates. The ∼5000 deg
2
wide-area survey footprint is shown in red. The eight shallow SN fi elds are shown as
blue circles, and the two deep SN fields are shown as red circles. The Milky Way plane is shown as a solid line, with dashed lines at b= ±10 deg. The Galactic center
(cross) and south Galactic pole (plus sign) are also marked. The Large and Small Magellanic Clouds are indicated in gray. The inset panel shows an overlay of co-add
processing units, co-add tiles, on top of the SDSS Stripe 82 area. This and the other sky map plots included in this work use the equal-area McBryde–Thomas flat-
polar quartic projection.
82
Two and a half DECam CCDs have failed over the course of DES operation
and are only included in DR1 when operating properly (Diehl et al. 2014;
Flaugher et al. 2015; Morganson et al. 2018).
83
Beginning in Y4, Y-band exposure times were increased to 90
s
to reduce
overhead while maintaining the same cumulative exposure target.
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The Astrophysical Journal Supplement Series, 239:18 (25pp), 2018 December Abbott et al.
brightness levels for single-epoch images; the median sky
brightness is g=22.01, r=21.15, i =19.89, z=18.72, and
=
-
Y
17.96 mag arcsec
2
. The resulting median single-epoch
effective image noise level (square root of the calibrated image
variance), including additional contributions from read noise
and shot noise of the dome flat, is
=g 25.25
, r=24.94,
i=24.31, z=23.58, and
=
-
Y
22.28 mag arcsec
2
.
Each position in the DES DR1 footprint is typically covered
by three to five overlapping DECam exposures in each of the
grizY bands (Figure 5). As an example, a map for the number of
overlapping i-band exposures across the footprint is shown in
Figure 6.
The total sky coverage of DR1 was estimated using maps
of the individual image coverage generated by mangle
(Hamilton & Tegmark 2004; Swanson et al. 2008) and
converted to HEALPix (Górski et al. 2005) maps with spatial
resolution comparable to the size of gaps between individual
CCDs (
n
sid
e
=4096, ∼0 86; Drlica-Wagner et al. 2018).
When requiring at least one exposure in a given band, the areal
coverage of each individual band is
=g 522
4
, r=5231,
i=5230, z= 5234, and Y =5227 deg
2
. When requiring
at least one exposure in all of the grizY bands, the DR1
footprint area is 5186 deg
2
. These areal coverage numbers do
not account for regions that are masked around bright stars or
masked owing to other imaging artifacts, which decrease the
areal coverage by ∼200 deg
2
. Note also that we are not
releasing mangle products for DR1. Instead, we are providing
HEALPix indices for all the objects at different resolutions, as
well as a tabulated HEALPix map with
n
sid
e
=32 for the
footprint. See Section 6 for more details about these products.
3. Data Release Processing
We briefly describe the DESDM processing pipeline applied
to the DES data to generate the DR1 data products.
84
DR1 is
based on the DESDM Y3A2 internal release to the DES
Collaboration, referring to the second annual release of data
products obtained from the first three seasons of DES science
operations and the Science Verification period. Where possible,
Figure 3. Normalized histograms showing the distribution of PSF FHWM for
single-epoch images that form the DR1 co-add.
Figure 4. Normalized histograms showing the distribution of sky brightness for
single-epoch images that form the DR1 co-add. All magnitudes are given in the
AB system.
Figure 5. Histograms showing the distribution of overlapping images in each
of the grizY bands normalized over the DR1 footprint. Most regions of the
footprint are covered with three to five images.
Figure 6. Map of the DES footprint showing the number of overlapping i-band
exposures. Regions of above-average coverage are a consequence of the DES
hexagonal layout scheme and can be found at intervals of ΔR.A.=30°. Color
range units are number of exposures.
84
Note that the DESDM pipeline differs from the DECam community
pipeline.
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The Astrophysical Journal Supplement Series, 239:18 (25pp), 2018 December Abbott et al.
