Cosmological Constraints from Multiple Probes in the Dark Energy Survey
DES Collaboration, T. M. C. Abbott, A. Alarcon, S. Allam, P. Andersen, F. Andrade-Oliveira, J. Annis, J. Asorey, A. Avelino, S. Avila, D. Bacon, N. Banik, B. A. Bassett, E. Baxter, K. Bechtol, M. R. Becker, G. M. Bernstein, E. Bertin, J. Blazek, S. L. Bridle, D. Brooks, D. Brout, D. L. Burke, J. Calcino, H. Camacho, A. Campos, A. Carnero Rosell, D. Carollo, M. Carrasco Kind, J. Carretero, F. J. Castander, R. Cawthon, P. Challis, K. C. Chan, C. Chang, M. Childress, A. Clocchiatti, M. Crocce, C. E. Cunha, C. B. D'Andrea, L. N. da Costa, C. Davis, T. M. Davis, J. De Vicente, D. L. DePoy, J. DeRose, S. Desai, H. T. Diehl, J. P. Dietrich, S. Dodelson, P. Doel, A. Drlica-Wagner, T. F. Eifler, J. Elvin-Poole, J. Estrada, A. E. Evrard, E. Fernandez, A. V. Filippenko, B. Flaugher, R. J. Foley, P. Fosalba, J. Frieman, L. Galbany, J. García-Bellido, M. Gatti, E. Gaztanaga, D. W. Gerdes, T. Giannantonio, K. Glazebrook, D. A. Goldstein, D. Gruen, R. A. Gruendl, J. Gschwend, G. Gutierrez, W. G. Hartley, S. R. Hinton, D. L. Hollowood, K. Honscheid, J. K. Hoormann, B. Hoyle, D. Huterer, B. Jain, D. J. James, M. Jarvis, T. Jeltema, E. Kasai, S. Kent, R. Kessler, A. G. Kim, R. P. Kirshner, N. Kokron, E. Krause, R. Kron, K. Kuehn, N. Kuropatkin, O. Lahav, J. Lasker, P. Lemos, G. F. Lewis, T. S. Li, et al. (69 additional authors not shown)
DDES-2018-0401FERMILAB-PUB-18-585-AE
Cosmological Constraints from Multiple Probes in the Dark Energy Survey
T. M. C. Abbott, A. Alarcon,
2, 3
S. Allam, P. Andersen,
5, 6
F. Andrade-Oliveira,
7, 8
J. Annis, J. Asorey, S. Avila, D. Bacon, N. Banik, B. A. Bassett,
11, 12
E. Baxter, K. Bechtol,
14, 15
M. R. Becker, G. M. Bernstein, E. Bertin,
17, 18
J. Blazek,
19, 20
S. L. Bridle, D. Brooks, D. Brout, D. L. Burke,
23, 24
J. Calcino, H. Camacho,
25, 8
A. Campos,
26, 7
A. Carnero Rosell,
27, 8
D. Carollo, M. Carrasco Kind,
29, 30
J. Carretero, F. J. Castander,
2, 3
R. Cawthon, P. Challis, K. C. Chan,
2, 3
C. Chang,
33, 34
M. Childress, M. Crocce,
2, 3
C. E. Cunha, C. B. D’Andrea, L. N. da Costa,
8, 36
C. Davis, T. M. Davis, J. De Vicente, D. L. DePoy, J. DeRose,
38, 23
S. Desai, H. T. Diehl, J. P. Dietrich,
40, 41
S. Dodelson, P. Doel, A. Drlica-Wagner,
4, 34
T. F. Eifler,
42, 43
J. Elvin-Poole,
19, 44
J. Estrada, A. E. Evrard,
45, 46
E. Fernandez, B. Flaugher, R. J. Foley, P. Fosalba,
2, 3
J. Frieman,
4, 34
L. Galbany, J. Garc´ıa-Bellido, M. Gatti, E. Gaztanaga,
2, 3
D. W. Gerdes,
45, 46
T. Giannantonio,
50, 51, 52
K. Glazebrook, D. A. Goldstein, D. Gruen,
38, 23, 24
R. A. Gruendl,
29, 30
J. Gschwend,
8, 36
G. Gutierrez, W. G. Hartley,
22, 55
S. R. Hinton, D. L. Hollowood, K. Honscheid,
19, 44
J. K. Hoormann, B. Hoyle,
56, 52
D. Huterer, B. Jain, D. J. James, M. Jarvis, T. Jeltema, E. Kasai,
58, 12
S. Kent,
4, 34
R. Kessler,
33, 34
A. G. Kim, N. Kokron,
38, 23
E. Krause, R. Kron,
4, 34
K. Kuehn, N. Kuropatkin, O. Lahav, J. Lasker,
33, 34
P. Lemos,
22, 50, 51
G. F. Lewis, T. S. Li,
4, 34
C. Lidman, M. Lima,
25, 8
H. Lin, E. Macaulay, N. MacCrann,
19, 44
M. A. G. Maia,
8, 36
M. March, J. Marriner, J. L. Marshall, P. Martini,
19, 63
R. G. McMahon,
50, 51
P. Melchior, F. Menanteau,
29, 30
R. Miquel,
65, 31
J. J. Mohr,
40, 41, 56
E. Morganson, J. Muir, A. M¨oller,
66, 62
E. Neilsen, R. C. Nichol, B. Nord, R. L. C. Ogando,
8, 36
A. Palmese, Y.-C. Pan,
67, 68
H. V. Peiris, W. J. Percival,
69, 70
A. A. Plazas, A. Porredon,
2, 3
J. Prat, A. K. Romer, A. Roodman,
23, 24
R. Rosenfeld,
72, 8
A. J. Ross, E. S. Rykoff,
23, 24
S. Samuroff, C. S´anchez, E. Sanchez, V. Scarpine, R. Schindler, M. Schubnell, D. Scolnic, L. F. Secco, S. Serrano,
2, 3
I. Sevilla-Noarbe, R. Sharp, E. Sheldon, M. Smith, M. Soares-Santos, F. Sobreira,
75, 8
N. E. Sommer,
66, 62
E. Swann, M. E. C. Swanson, G. Tarle, D. Thomas, R. C. Thomas, M. A. Troxel, B. E. Tucker,
66, 62
S. A. Uddin, P. Vielzeuf, A. R. Walker, M. Wang, N. Weaverdyck, R. H. Wechsler,
38, 23, 24
J. Weller,
40, 56, 52
B. Yanny, B. Zhang,
66, 62
Y. Zhang, and J. Zuntz (DES Collaboration) Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, Casilla 603, La Serena, Chile Institut d’Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain Institute of Space Sciences (ICE, CSIC), Campus UAB,Carrer de Can Magrans, s/n, 08193 Barcelona, Spain Fermi National Accelerator Laboratory, P. O. Box 500, Batavia, IL 60510, USA School of Mathematics and Physics, University of Queensland, Brisbane, QLD 4072, Australia University of Copenhagen, Dark Cosmology Centre, Juliane Maries Vej 30, 2100 Copenhagen O Instituto de F´ısica Te´orica, Universidade Estadual Paulista, S˜ao Paulo, Brazil Laborat´orio Interinstitucional de e-Astronomia - LIneA,Rua Gal. Jos´e Cristino 77, Rio de Janeiro, RJ - 20921-400, Brazil Korea Astronomy and Space Science Institute, Yuseong-gu, Daejeon, 305-348, Korea Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth, PO1 3FX, UK African Institute for Mathematical Sciences, 6 Melrose Road, Muizenberg, 7945, South Africa South African Astronomical Observatory, P.O.Box 9, Observatory 7935, South Africa Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104, USA LSST, 933 North Cherry Avenue, Tucson, AZ 85721, USA Physics Department, 2320 Chamberlin Hall, University of Wisconsin-Madison, 1150 University Avenue Madison, WI 53706-1390 Argonne National Laboratory, 9700 South Cass Avenue, Lemont, IL 60439, USA CNRS, UMR 7095, Institut d’Astrophysique de Paris, F-75014, Paris, France Sorbonne Universit´es, UPMC Univ Paris 06, UMR 7095,Institut d’Astrophysique de Paris, F-75014, Paris, France Center for Cosmology and Astro-Particle Physics, The Ohio State University, Columbus, OH 43210, USA Institute of Physics, Laboratory of Astrophysics, ´Ecole Polytechnique F´ed´eralede Lausanne (EPFL), Observatoire de Sauverny, 1290 Versoix, Switzerland Jodrell Bank Center for Astrophysics, School of Physics and Astronomy,University of Manchester, Oxford Road, Manchester, M13 9PL, UK Department of Physics & Astronomy, University College London, Gower Street, London, WC1E 6BT, UK Kavli Institute for Particle Astrophysics & Cosmology,P. O. Box 2450, Stanford University, Stanford, CA 94305, USA SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA Departamento de F´ısica Matem´atica, Instituto de F´ısica,Universidade de S˜ao Paulo, CP 66318, S˜ao Paulo, SP, 05314-970, Brazil Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15312, USA Centro de Investigaciones Energ´eticas, Medioambientales y Tecnol´ogicas (CIEMAT), Madrid, Spain a r X i v : . [ a s t r o - ph . C O ] M a y INAF, Astrophysical Observatory of Turin, I-10025 Pino Torinese, Italy Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 W. Green Street, Urbana, IL 61801, USA National Center for Supercomputing Applications, 1205 West Clark St., Urbana, IL 61801, USA Institut de F´ısica d’Altes Energies (IFAE), The Barcelona Institute ofScience and Technology, Campus UAB, 08193 Bellaterra (Barcelona) Spain Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL 60637, USA Kavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637, USA School of Physics and Astronomy, University of Southampton, Southampton, SO17 1BJ, UK Observat´orio Nacional, Rua Gal. Jos´e Cristino 77, Rio de Janeiro, RJ - 20921-400, Brazil 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 Department of Physics, Stanford University, 382 Via Pueblo Mall, Stanford, CA 94305, USA Department of Physics, IIT Hyderabad, Kandi, Telangana 502285, India Excellence Cluster Universe, Boltzmannstr. 2, 85748 Garching, Germany Faculty of Physics, Ludwig-Maximilians-Universit¨at, Scheinerstr. 1, 81679 Munich, Germany Department of Astronomy/Steward Observatory, 933 North Cherry Avenue, Tucson, AZ 85721-0065, USA Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109, USA Department of Physics, The Ohio State University, Columbus, OH 43210, USA Department of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA Department of Physics, University of Michigan, Ann Arbor, MI 48109, USA Santa Cruz Institute for Particle Physics, Santa Cruz, CA 95064, USA PITT PACC, Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA 15260, USA Instituto de Fisica Teorica UAM/CSIC, Universidad Autonoma de Madrid, 28049 Madrid, Spain Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK Universit¨ats-Sternwarte, Fakult¨at f¨ur Physik, Ludwig-Maximilians Universit¨at M¨unchen, Scheinerstr. 1, 81679 M¨unchen, Germany Centre for Astrophysics & Supercomputing, Swinburne University of Technology, Victoria 3122, Australia California Institute of Technology, 1200 East California Blvd, MC 249-17, Pasadena, CA 91125, USA Department of Physics, ETH Zurich, Wolfgang-Pauli-Strasse 16, CH-8093 Zurich, Switzerland Max Planck Institute for Extraterrestrial Physics, Giessenbachstrasse, 85748 Garching, Germany Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA Department of Physics, University of Namibia, 340 Mandume Ndemufayo Avenue, Pionierspark, Windhoek, Namibia Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA Australian Astronomical Optics, Macquarie University, North Ryde, NSW 2113, Australia Sydney Institute for Astronomy, School of Physics, A28, The University of Sydney, NSW 2006, Australia The Research School of Astronomy and Astrophysics, Australian National University, ACT 2601, Australia Department of Astronomy, The Ohio State University, Columbus, OH 43210, USA Department of Astrophysical Sciences, Princeton University, Peyton Hall, Princeton, NJ 08544, USA Instituci´o Catalana de Recerca i Estudis Avanc¸ats, E-08010 Barcelona, Spain ARC Centre of Excellence for All-sky Astrophysics (CAASTRO) Division of Theoretical Astronomy, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan Institute of Astronomy and Astrophysics, Academia Sinica, Taipei 10617, Taiwan Department of Physics and Astronomy, University of Waterloo,200 University Ave W, Waterloo, ON N2L 3G1, Canada Perimeter Institute for Theoretical Physics, 31 Caroline St. North, Waterloo, ON N2L 2Y5, Canada Department of Physics and Astronomy, Pevensey Building, University of Sussex, Brighton, BN1 9QH, UK ICTP South American Institute for Fundamental ResearchInstituto de F´ısica Te´orica, Universidade Estadual Paulista, S˜ao Paulo, Brazil Brookhaven National Laboratory, Bldg 510, Upton, NY 11973, USA Brandeis University, Physics Department, 415 South Street, Waltham MA 02453 Instituto de F´ısica Gleb Wataghin, Universidade Estadual de Campinas, 13083-859, Campinas, SP, Brazil Department of Physics, Duke University, Durham, NC 27708, USA Observatories of the Carnegie Institution for Science, 813 Santa Barbara St., Pasadena, CA 91101, USA Institute for Astronomy, University of Edinburgh, Edinburgh EH9 3HJ, UK (Dated: May 7, 2019)The combination of multiple observational probes has long been advocated as a powerful technique toconstrain cosmological parameters, in particular dark energy. The Dark Energy Survey has measured 207spectroscopically–confirmed Type Ia supernova lightcurves; the baryon acoustic oscillation feature; weak gravi-tational lensing; and galaxy clustering. Here we present combined results from these probes, deriving constraintson the equation of state, w , of dark energy and its energy density in the Universe. Independently of other exper-iments, such as those that measure the cosmic microwave background, the probes from this single photometric survey rule out a Universe with no dark energy, finding w = − . +0 . − . . The geometry is shown to be consis-tent with a spatially flat Universe, and we obtain a constraint on the baryon density of Ω b = 0 . +0 . − . thatis independent of early Universe measurements. These results demonstrate the potential power of large multi-probe photometric surveys and pave the way for order of magnitude advances in our constraints on propertiesof dark energy and cosmology over the next decade. Keywords: dark energy; dark matter; cosmology: observations; cosmological parameters
INTRODUCTION
The discovery of the accelerating Universe [1, 2] revolu-tionized 20th century cosmology by indicating the presence ofa qualitatively new component in the Universe that dominatesthe expansion in the last several billion years. The nature ofdark energy — the component that causes the accelerated ex-pansion — is unknown, and understanding its properties andorigin is one of the principal challenges in modern physics.Current measurements are consistent with an interpretation ofdark energy as a cosmological constant in General Relativity.Any deviation from this interpretation in space or time wouldconstitute a landmark discovery in fundamental physics [3].Dark energy leaves imprints on cosmological observations,typically split into two regimes — 1) it modifies the geome-try of the Universe, increasing distances and volumes in theUniverse over time via the accelerated expansion, and 2) itsuppresses the growth of cosmic structure. However, these ef-fects can be mimicked by the variation of other cosmologicalparameters, including the dark matter density and curvature,or other physical models and systematics that are degeneratewithin a single probe. Consequently, measuring dark energyproperties requires a combination of cosmological probes thatare sensitive to both classes of effects to break these parameterand model degeneracies [4–6].Historically, the most powerful cosmic probe has been thecosmic microwave background (CMB) [7–9], relic radiationfrom the surface of last scattering only 400,000 years after theBig Bang. Low-redshift probes measure the Universe overthe last several billion years, when dark energy dominates theexpansion. Comparing or combining constraints between theCMB and lower redshift measurements requires us to extrapo-late predictions to the present-day Universe starting from ini-tial conditions over 13 billion years ago. This is a powerfultest of our models, but it requires precise, independent con-straints from low-redshift experiments. Low-redshift probesinclude Type Ia supernova (SNe Ia) measurements, whichtreat the SNe Ia as standardizable candles and employ red-shift and flux measurements to probe the redshift-luminositydistance relation [10]; baryon acoustic oscillations (BAO),which use a ‘standard ruler’ scale in the cosmic density field,imprinted by sound waves at recombination, to probe sev-eral redshift-distance combinations [11, 12]; galaxy cluster-ing, which measures the density field up to some bias be-tween galaxy density and the underlying dark matter density,and redshift-space distortions (RSD) in the clustering [13]; thecounts of galaxy clusters, representing the most extreme den-sity peaks in the Universe [14]; strong gravitational lensing [15]; and weak gravitational lensing, which probes changes inthe gravitational potential along the line of sight using coher-ent distortions in observed properties of galaxies or the CMB,e.g. to measure the dark and baryonic matter distribution [16].We report here the first results from the Dark Energy Sur-vey (DES) combining precision probes of both geometry andgrowth of structure that include BAO, SNe Ia, and weak lens-ing and galaxy clustering from a single experiment. DEShas previously shown separate cosmological constraints us-ing weak lensing and galaxy clustering [17], BAO [18], andSNe Ia [19]. We now combine these probes and begin to fullyrealize the power of this multi-probe experiment to produceindependent measurements of the properties of dark energy.The work presented here demonstrates our ability to extractand combine diverse cosmological observables from wide-field surveys of the evolved Universe. Previous dark energyconstraints have relied on combining the likelihoods of manyseparate and independent experiments to produce precise con-straints on cosmological models including dark energy. Forthis traditional approach each experiment has performed anindependent analysis to validate measurements and has sepa-rate calibration methodologies and requirements, thus ensur-ing that many potential systematics are uncorrelated betweenprobes. The DES analysis presented here, however, uses acommon set of both calibration methodologies and system-atics modeling and marginalization across probes, which en-ables a consistently validated analysis. Perhaps most impor-tantly, this common framework allows us to standardize re-quirements like blinding across these probes, which is essen-tial to minimize the impact of experimenter bias [20]. Thisapproach provides a very robust, precise cross-check of tra-ditional multi-probe analyses, which currently provide tighteroverall constraints.The fundamental interest in understanding the nature ofdark energy has spurred the development of multiple largephotometric surveys that image the sky, capable of indepen-dently combining multiple cosmic probes. The current gen-eration of surveys includes the Hyper-Suprime Cam survey(HSC) [21], the Kilo-Degree Survey (KiDS) [22], and the fo-cus of this work, DES [23]. The next generation of thesesurveys will include the Large Synoptic Survey Telescope(LSST) [24], a ground-based telescope that will observe theentire southern hemisphere with very high cadence, and spacetelescopes Euclid [25] and the Wide-Field InfraRed SurveyTelescope (WFIRST) [26]. In parallel with imaging surveys,the distribution of galaxies measured by spectroscopic surveys(i.e., BOSS [27], eBOSS [28], and the planned 4MOST [29],DESI [30], and PFS [31] surveys) provides powerful con-straints on the distance-redshift relation via BAO measure-ments and the growth of structure via redshift space distor-tions. The union of these results over the following severalyears, and into the next decades, will ensure that we are ableto take advantage of the benefits of multiple independent, self-consistent, and blinded multi-probe analyses like we presenthere for DES.
COSMIC PROBESThe Dark Energy Survey
DES cosmic probes span a wide range of redshifts up to z ≈ . , and include weak gravitational lensing and galaxyclustering due to large-scale structure [17], SNe Ia [19], andBAO [18]. Each probe constrains dark energy independentlyand their combination is more powerful. These probes uti-lize a subset of data from DES taken during its first threeobserving seasons (Aug. 2013 to Feb. 2016). Spectroscopi-cally confirmed SNe Ia are identified from images in all threeseasons (DES Y3) in 27 deg of repeated deep-field obser-vations, while weak lensing and large-scale structure infor-mation is derived from images taken only in the first season(DES Y1), ending Feb. 2014 and covering 1321 deg of thesouthern sky in grizY filters. DES uses the 570-megapixelDark Energy Camera (DECam [32]) at the Cerro Tololo Inter-American Observatory (CTIO) 4m Blanco telescope in Chile.By the end of DES observations in January 2019, we antici-pate an order of magnitude increase in the number of useableSNe, while the area of sky used for the other probes will in-crease by a factor of three to 5000 deg . Analysis of the lateryears of survey data is ongoing.Data is processed through the DES Data Management sys-tem [33–36]. This system detrends and calibrates the raw im-ages, creates coadded images from individual exposures, anddetects and catalogs astrophysical objects. This catalog is fur-ther cleaned and calibrated to create a high-quality (‘Gold’)object catalog [37] from which weak lensing and large-scalestructure measurements are made. The deep fields are alsoprocessed through a separate difference imaging pipeline toidentify transients [38, 39]. The photometric and astromet-ric calibrations [37] are common to all cosmology probes dis-cussed below. Weak Gravitational Lensing and Large-Scale Structure
For weak gravitational lensing measurements, we use themeasured shapes and positions of 26 million galaxies in theredshift range . < z < . , split into four redshift bins.The galaxy shapes are measured via the M ETACALIBRATION method [40, 41] using riz -band exposures [42]. Photomet-ric redshifts for the objects are determined from a modifiedversion of the BPZ method [43], described and calibrated inRef. [44]. For measurements of the angular galaxy clustering, we uti-lize the positions of a sample of luminous red galaxies thathave precise photometric redshifts selected with the
RED -M A G I C algorithm [45]. This results in a sample of 650,000galaxies over the redshift range . < z < . , split intofive narrow redshift bins. Residual correlations of numberdensity with survey conditions in the RED M A G I C sample arecalibrated in Ref. [46]. The precise redshifts of
RED M A G I Cgalaxies allow us to infer information about the more poorlyconstrained photo- z bias uncertainty in the weak lensing cat-alog. The photo- z calibration methodology is consistent be-tween the weak lensing and RED M A G I C samples [44, 47–49].We use measurements from each of these galaxy samples toconstruct a set of three two-point correlation function observ-ables we label ‘3 × × OSMO
SIS [55]. This combination of probesproduces a tight constraint on the amplitude of matter cluster-ing in the Universe and on the properties of dark energy overthe last six billion years.
Type Ia Supernovae
The DES-SN sample is comprised of 207 spectroscopicallyconfirmed SNe Ia in the redshift range . < z < . .The sample-building and analysis pipelines are discussed ina series of papers that detail the SN Ia search and discov-ery [36, 38, 39]; spectroscopic follow-up [56]; photome-try [57]; calibration [58, 59]; simulations [60]; and tech-nique of accounting for selection bias [61, 62]. The analy-sis methodology and systematic uncertainties are presented inRef. [63]. These results are used to constrain cosmology [19]and the Hubble constant [64]. In Refs. [19, 63, 64] the DES-SN sample is combined with a ‘Low- z ’ ( z < . ) sample,which includes SNe from the Harvard-Smithsonian Center forAstrophysics surveys [65, 66] and the Carnegie SupernovaProject [67]. Selection effects and calibration of these low-redshift samples is discussed in [10]. Here we fit for DES-SN alone, and only include the Low- z sample for comparisonto Ref. [19]. We compute the SNe likelihood using the SNemodule [10] implemented in C OSMO
SIS, which is able to re-produce the results in [19].
Baryon Acoustic Oscillations
A sample of 1.3 million galaxies from the DES Y1 ‘Gold’catalog in the redshift range . < z < . was used tomeasure the BAO scale in the distribution of galaxies. De-tails of the galaxy sample selection are in Ref. [68]. Calibra-tions of the galaxy selection function are consistently derivedfor the BAO and ‘3 × D A ( z = 0 . , and the sound horizon at the drag epoch, r d .This analysis used 1800 simulations [69] and three methods tocompute the galaxy clustering [70–72]. The BAO likelihoodis implemented in C OSMO
SIS. The galaxy samples used inthe ‘3 × . < z < . ,which will produce some non-zero correlation between thetwo measurements. However, the intersection of the galaxypopulations is only about 14% of the total BAO galaxy sam-ple and we detect no significant BAO constraint when usingthe ‘3x2pt’ galaxy clustering measurements. We thus ignorethis negligible correlation when combining the two probes. External Data for Comparison
We use external constraints that combine state-of-the-artCMB, SNe Ia, and spectroscopic BAO measurements to com-pare our results against. For the CMB data, we utilize full-skytemperature ( T ) and polarization ( E - and B -mode) measure-ments from the Planck survey, combining T T ( (cid:96) ∈ [2 , ),and EE , BB and T E ( (cid:96) ∈ [2 , ) (commonly referred to as‘TT+LowP’) [73] with weak lensing measurements derivedfrom the temperature data [74]. We use the Planck likelihoodfrom Ref. [75].For external SNe Ia measurements, we use the Pantheoncompilation [10]. Pantheon combines SNe Ia samples fromPan-STARRS1, SDSS, SNLS, various low- z data sets, andHST. The Pantheon data set is based on the Pan-STARRS1Supercal algorithm [76] that establishes a global calibrationfor the 13 different SNe Ia samples, with a total of 1048 SNein . < z < . .Finally, external spectroscopic BAO measurements aretaken from BOSS DR12 [13], the 6dF Galaxy Survey [77],and the SDSS Main Galaxy Sample [78]. These measure-ments of the BAO scale span a redshift range of . < z < . . CONSTRAINTS ON DARK ENERGY
We present here a dark energy analysis that combines forthe first time the DES probes described above. DES is ableto strongly constrain dark energy models without the CMBby probing over a wide redshift range ( z (cid:46) ) the growth ofstructure and distance-redshift relation, which are both sensi-tive to the presence of dark energy. The dark energy equationof state w relates the pressure ( P ) to the energy density ( ρ ) ofthe dark energy fluid: w = P/ρ , where w = − is equivalentto a cosmological constant Λ in the field equations. We probe TABLE I. Cosmological parameter constraints in the o CDM and w CDM models using only DES data. We report the 1D peak ofthe posterior and asymmetric 68% confidence limits. The marginal-ized parameters with informative priors (and prior ranges) are: theprimordial perturbation amplitude A s ∈ [0 . , . , the Hubbleconstant H ∈ [55 , km s − Mpc − , the spectral index n s ∈ [0 . , . , and the neutrino mass density Ω ν h ∈ [0 . , . .Parameter o CDM w CDM w CDM (Ext) Flat Prior Ω m . +0 . − . . +0 . − . . +0 . − . [0.1, 0.9] Ω b . +0 . − . . +0 . − . . +0 . − . [0.03, 0.12] Ω k . +0 . − . Ω Λ . +0 . − . . +0 . − . . +0 . − . Derived w − − . +0 . − . − . +0 . − . [-2, -0.33] S . +0 . − . . +0 . − . . +0 . − . Derived the nature of dark energy in two ways: 1) we constrain thedark energy density relative to the critical density today, Ω Λ ,assuming that dark energy takes the form of a cosmologicalconstant and allowing non-zero curvature (the o CDM model),and 2) we measure w as a free parameter (the w CDM model)with fixed curvature ( Ω k = 0 ). The total energy density of theUniverse today is composed of the sum of fractional compo-nents k + Ω m + Ω Λ , where the components are: curva-ture ( Ω k ), the total matter ( Ω m ), and dark energy ( Ω Λ ). Theradiation density is assumed to be negligible over the redshiftranges probed by DES.In both o CDM and w CDM models, we explore the abilityof DES to constrain these properties of dark energy and com-pare this to the state-of-the-art constraints combining mea-surements from many external surveys. We follow the analy-sis methods and model definitions from Ref. [17], which in-cludes varying the neutrino mass density in all models. Exter-nal data are re-analyzed to make direct comparisons meaning-ful, including matching parameter choices and priors to theDES analysis. The cosmological parameters and their pri-ors are slightly changed from Ref. [17] and listed in TableI. Non-cosmological parameters and their priors are identi-cal to Table 1 of Ref. [17], with the absolute magnitude − . < M < − . for SNe. Cosmological parametersand the intrinsic alignment model (for ‘3 × Ω Λ in the o CDM model,where w = − . We combine our ‘3 × z sample), and photometric BAO measurementsto constrain Ω Λ and Ω m . This is compared to the constraintfrom the external data sets. The DES best-fit χ is 576 with498 degrees of freedom (dof) [79]. Using DES data we areable to independently confirm the existence of a dark energy Ω m Ω Λ A cc e l e r a t i n g t o d a y D e c e l e r a t i n g t o d a y F l a t U n i v e r s e DES (3x2pt+SNe+Phot. BAO)DES SNeEXT (CMB+SNe+Spec. BAO)
FIG. 1. Constraints on the present-day dark energy density Ω Λ andmatter density Ω m , relative to the critical density, in an o CDM modelwith marginalized curvature and neutrino mass density. We comparethe constraint from DES data alone (black contours), including infor-mation from weak gravitational lensing, large-scale structure, SNeIa, and photometric BAO, to the best available external data (greencontours), combining information from the CMB, SNe Ia, and spec-troscopic BAO. We identify the flat model ( Ω k = 0 ) with a dottedline and distinguish accelerating and decelerating universes with adashed line. Contours represent the 68% and 95% confidence limits(CL). component in the Universe ( Ω Λ > ) at ∼ σ significance.This is the first time a photometric survey has independentlymade a significant constraint on the energy density of bothdark energy and dark matter without assuming a flat modelbased on early Universe constraints. It represents an impor-tant milestone for future analyses from DES and surveys likeEuclid, LSST, and WFIRST.In Fig. 2, we show the constraint on w and Ω m , assumingthe w CDM model. We show the same comparison with exter-nal data as in Fig. 1, but also include a case where we supple-ment DES-discovered SNe Ia with the Low- z SNe sample toanchor the SNe redshift-distance relation at low redshift fol-lowing Ref. [19]. This low-redshift SNe anchor contributessignificantly to both the DES+Low- z and external constraintson w . In all cases, the existing data are consistent with a cos-mological constant ( w = − ). The DES best-fit χ is 577with 498 dof. This subset of the final DES data constrains w to within a factor of three of the combined external constraint.This result illustrates the prospects for multiple independent,precise low-redshift constraints on dark energy from upcom-ing large-scale photometric experiments.The constraints on all cosmological model parameters are Ω m w DES (3x2pt+SNe+Phot. BAO)DES SNeDES + Low- z SNeEXT (CMB+SNe+Spec. BAO)
FIG. 2. Constraints on the dark energy equation of state w and Ω m in a w CDM model with fixed curvature ( Ω k = 0 ) and marginal-ized neutrino mass density. We compare constraints from the DESdata alone (black contours) to the best available external data (greencontours), as in Fig. 1, but also show the impact of including a low-redshift SNe Ia data set (Low- z ) to anchor the DES SNe Ia as donein Ref. [19] (blue contours). Each component of the DES analysiswas fully blinded. summarized in Table I. Nuisance parameter constraints are notqualitatively changed from individual probe fits. The DES-only ‘3 × w and Ω Λ . In the o CDM model, DES constrains the total matter density to 7%(68% CL), the baryon density to 15%, and the correlationamplitude to 3%, described by S ≡ σ (cid:112) Ω m / . , where σ measures the current-day clustering amplitude. The con-straints are comparable in w CDM. Fixing Ω k = 0 , we find the S constraint is improved by a factor of 1.2, but there is oth-erwise no significant improvement in other parameters. Theparameter constraints beyond dark energy are driven by the‘3 × Ω b from the CMB, by contrast, is also sensitive to the impact ofbaryons on the acoustic oscillations. Thus future low-redshiftsurvey data will provide another avenue to test the predictionsof our models from early Universe observations like the CMBwith measurements of Ω b from surveys like DES. OUTLOOK
The most precise constraints on dark energy properties re-quire combining cosmological probes that include informa-tion from both geometry and growth across cosmic history.Thus far such diverse information was collected from differentexperiments, which were subject to different calibration andsystematic errors. We have combined for the first time in DESthe purely cosmographic SN and BAO measurements with thegrowth-sensitive weak lensing and galaxy clustering measure-ments to independently place strong constraints on the natureof dark energy. These results share a common set of cali-bration frameworks and blinding policy across probes. DEShas independently constrained Ω m , Ω b , Ω Λ , σ , and w , whilemarginalizing over a free neutrino mass. We expect futureDES results to provide a further factor of 2-4 improvementin these constraints due to increased area, depth, and numberof SNe in the final analyses, which will then be followed bysubsequent order of magnitude advances from more sensitivephotometric surveys of the 2020s. ACKNOWLEDGEMENTS
Funding for the DES Projects has been provided by theDOE and NSF (USA), MEC/MICINN/MINECO (Spain),STFC (UK), HEFCE (UK), NCSA (UIUC), KICP (U.Chicago), CCAPP (Ohio State), MIFPA (Texas A&M),CNPQ, FAPERJ, FINEP (Brazil), DFG (Germany) and theCollaborating Institutions in the Dark Energy Survey.The Collaborating Institutions are Argonne Lab, UC SantaCruz, University of Cambridge, CIEMAT-Madrid, Universityof Chicago, University College London, DES-Brazil Con-sortium, University of Edinburgh, ETH Z¨urich, Fermilab,University of Illinois, ICE (IEEC-CSIC), IFAE Barcelona,Lawrence Berkeley Lab, LMU M¨unchen and the associatedExcellence Cluster Universe, University of Michigan, NOAO,University of Nottingham, Ohio State University, Universityof Pennsylvania, University of Portsmouth, SLAC NationalLab, Stanford University, University of Sussex, Texas A&MUniversity, and the OzDES Membership Consortium.Based in part on observations at Cerro Tololo Inter-American Observatory, National Optical Astronomy Observa-tory, which is operated by the Association of Universities forResearch in Astronomy (AURA) under a cooperative agree-ment with the National Science Foundation.The DES Data Management System is supported bythe NSF under Grant Numbers AST-1138766 and AST-1536171. The DES participants from Spanish institutionsare partially supported by MINECO under grants AYA2015-71825, ESP2015-66861, FPA2015-68048, SEV-2016-0588,SEV-2016-0597, and MDM-2015-0509, some of which in-clude ERDF funds from the European Union. IFAE ispartially funded by the CERCA program of the Generali-tat de Catalunya. Research leading to these results has re-ceived funding from the European Research Council under the European Union’s Seventh Framework Program (FP7/2007-2013) including ERC grant agreements 240672, 291329, and306478. We acknowledge support from the Australian Re-search Council Centre of Excellence for All-sky Astrophysics(CAASTRO), through project number CE110001020, and theBrazilian Instituto Nacional de Ciˆencia e Tecnologia (INCT)e-Universe (CNPq grant 465376/2014-2).This manuscript has been authored by Fermi Research Al-liance, LLC under Contract No. DE-AC02-07CH11359 withthe U.S. Department of Energy, Office of Science, Office ofHigh Energy Physics. The United States Government retainsand the publisher, by accepting the article for publication, ac-knowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publishor reproduce the published form of this manuscript, or allowothers to do so, for United States Government purposes.This research used resources of the National Energy Re-search Scientific Computing Center, a DOE Office of Sci-ence User Facility supported by the Office of Science of theU.S. Department of Energy under Contract No. DE-AC02-05CH11231. This work also used resources on the CCAPPcondo of the Ruby Cluster at the Ohio Supercomputing Cen-ter [81]. Plots in this manuscript were produced partly withM
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