The Dark Energy Survey

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The Dark Energy Survey (DES)
Huan Lin Experimental Astrophysics
Group Fermilab On behalf of the Dark Energy
Survey Collaboration
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The Dark Energy Survey (DES)

• Study Dark Energy using 4 complementary
  techniques
• Galaxy clusters
• Weak lensing
• Baryon acoustic oscillations
• Type Ia supernovae
• 2 Multiband Surveys
• 5000 deg2 griz survey of the Southern Galactic
  Cap
• 40 deg2 repeated for supernovae
• 525 nights (2009-2015) on the CTIO 4m Blanco
  telescope
• Build
• Large 3 deg2 mosaic CCD camera and optical
  corrector for the Blanco
• Data management system
• Response to NOAO AO

Blanco 4m Telescope at the Cerro-Tololo Inter-Ame
rican Observatory (CTIO)
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The DES Collaboration
Fermilab J. Annis, H. T. Diehl, S. Dodelson, J.
Estrada, B. Flaugher, J. Frieman, S. Kent, H.
Lin, P. Limon, K. W. Merritt, J. Peoples, V.
Scarpine, A. Stebbins, C. Stoughton, D. Tucker,
W. Wester University of Illinois at
Urbana-Champaign C. Beldica, R. Brunner, I.
Karliner, J. Mohr, R. Plante, P. Ricker, M.
Selen, J. Thaler University of Chicago J.
Carlstrom, S. Dodelson, J. Frieman, M. Gladders,
W. Hu, S. Kent, R. Kessler, E. Sheldon, R.
Wechsler Lawrence Berkeley National Lab N. Roe,
C. Bebek, M. Levi, S. Perlmutter University of
Michigan R. Bernstein, B. Bigelow, M. Campbell,
D. Gerdes, A. Evrard, W. Lorenzon, T. McKay, M.
Schubnell, G. Tarle, M. Tecchio NOAO/CTIO T.
Abbott, C. Miller, C. Smith, N. Suntzeff, A.
Walker CSIC/Institut d'Estudis Espacials de
Catalunya (Barcelona) F. Castander, P. Fosalba,
E. Gaztañaga, J. Miralda-Escude Institut de
Fisica d'Altes Energies (Barcelona) E.
Fernández, M. Martínez CIEMAT (Madrid) C. Mana,
M. Molla, E. Sanchez, J. Garcia-Bellido University
College London O. Lahav, D. Brooks, P. Doel, M.
Barlow, S. Bridle, S. Viti, J. Weller University
of Cambridge G. Efstathiou, R. McMahon, W.
Sutherland University of Edinburgh J. Peacock
University of Portsmouth R. Crittenden, R.
Nichol, W. Percival University of Sussex A.
Liddle, K. Romer
plus students
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Basic Survey Parameters

• 5000 deg2 Survey Area
• 4000 deg2 of overlap with South Pole Telescope
  (SPT) survey area
• Also includes SDSS Southern Equatorial Stripe
  deep galaxy redshift survey fields
• Limiting Magnitudes
• Galaxies 10s griz 24.6, 24.1, 24.3, 23.9
• Point sources 5s griz 26.1, 25.6, 25.8, 25.4
• Observation Strategy
• Multiple tilings/overlaps (in units of 100 sec
  exposures) to optimize photometric calibrations
• 2 survey tilings/filter/year
• 1 photometry goal

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The Dark Energy Camera (DECam)

• 5-element optical corrector
• 4 filters g,r,i,z
• 2k x 4k LBNL CCDs
• 0.27/pixel
• 62 CCD, 520 Megapixel mosaic camera
• 3 deg2 field of view

F8 Mirror
Filters Shutter
3556 mm
CCD Read out
Hexapod
Optical Lenses
1575 mm
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DES CCDs
DES CCD QE

• LBNL CCDs
• High quantum efficiency in the red QE gt 50 at
  1000 nm
• 250 ?m thick, 15 ?m pixels
• 17 sec readout time
• Optimal for z-band observations needed by DES for
  galaxies and clusters at redshifts 1 and above
• DES CCD wafers
• First lots have been delivered by Dalsa and
  finished by LBNL
• First devices are now being packaged, tested, and
  characterized at Fermilab

Current Mosaic II QE
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DES Data Management

• U. Illinois and NCSA lead the DM project
• DM System Requirements
• Reliably transfer 300GB/night for 525 nights
  from CTIO to U. Illinois/National Center for
  Supercomputing Applications (NCSA)
• Automatically process data with built-in quality
  assurance
• Archive the data products and serve the processed
  data to collaboration
• Provide community access to the archive 1 year
  after images were collected
• DM Team
• U. Illinois/NCSA, Fermilab and NOAO
• Additional DES collaborators
• Deliverables to DES and astronomical community
• DM System (High Performance Computing platforms
  and workstations)
• Pipeline middleware
• Astronomy modules
• Catalog database
• Image Archive
• Archived science ready DES data

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DES Simulations

• Yearly cycles of simulations provide data for
  development of data reduction pipelines and
  science analysis codes
• Completed Level 1 Simulations
• 500 deg2 galaxy catalog
• 500 GB of science images shapelets-based
• Ongoing Level 2 Simulations
• 5000 deg2 galaxy catalog
• 5 TB of science images
• Use collaboration computing resources, including
  FermiGrid and Barcelona Marenostrum supercomputer
• Recovery of input cosmology from catalogs
• Future Level 3 Simulations
• Suite of full-DES catalogs
• 1 year of DES imaging data
• Synergy with DOE SciDAC proposal to produce large
  cosmological simulations for dark energy studies
• Recovery of input cosmologies from catalogs and
  images

gri color composite of example Level 1 simulation
image
Parent N-body box for Level 2 catalog simulation
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DES Galaxy Clusters

• Galaxy cluster abundance, mass function, and
  correlations sensitive to cosmology via effects
  on volume and on growth rate of perturbations
• Complementary cluster samples
• DES optical data provide accurate cluster
  photometric redshifts
• South Pole Telescope (SPT) Sunyaev-Zeldovich
  effect (SZE) data provides robust cluster masses
• Tens of thousands of clusters in 4000 deg2 area
  of DES-SPT overlap
• Multiple cluster mass estimators (optical
  richness, SZ, lensing) and cross-checks of sample
  selection effects

from J. Mohr
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Cluster Mass-Observable Calibration

• Simulations indicate robust cluster mass vs. SZE
  flux decrement relationship

• Lensing will be used to calibrate cluster mass
  vs. optical richness relationship cf. SDSS

? Adiabatic ? CoolingStar Formation
SZE flux
SDSS Data Preliminary zlt0.3
small (10) scatter
Nagai, Motl, et al.
Johnston, Sheldon, et al., in preparation
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DES Weak Lensing
cosmic shear angular power spectrum in 4 redshift
bins

• Measure shapes for 300 million source galaxies
• Average galaxy redshift 0.7
• Effective galaxy surface density of 10 per
  arcmin2
• Shear-shear and galaxy-shear correlations probe
  distances and growth rate of perturbations
• Also provides independent calibration of cluster
  masses

from D. Huterer
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DES Weak Lensing

• Cerro Tololo Image Quality Sept-Feb
• site median PSF 0.65 FWHM
• Prime Focus (PF) delivered median PSF 0.9 FWHM
  (used in all DES constraint forecasts)
• DES/CTIO upgrades will stabilize the PSF and
  should improve the median FWHM
• DES
• focus and alignment sensors on focal plane
  generate focus and lateral alignment information
  with each image
• active control of camera position hexapods will
  provide focus and lateral adjustments of
  corrector camera system
• improved thermal environment heat dissipation
  will be actively controlled
• CTIO is upgrading the primary mirror radial
  supports to reduce mirror motions

(signal)
(old systematic)
(improved systematic)
Red expected signal
Results from 75 sq. deg. WL Survey with Mosaic II
and BTC on the Blanco 4-m (Bernstein et al.) DES
comparable depth source galaxies well resolved
bright low-risk
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DES Baryon Acoustic Oscillations

• Angular power spectrum of 300 million galaxies
  over 5000 deg2
• Measured in photo-z bins out to redshifts of 1
  and above
• Features in the angular power spectrum (e.g.
  horizon scale at matter-radiation equality,
  baryon oscillations) provide physically
  calibrated standard rods
• Allows measurement of angular diameter distances
  as a function of redshift to constrain cosmology

Acoustic series in P(k) becomes a single peak in
?(r)
SDSS galaxy correlation function
Eisenstein et al.
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DES ISW
s80.9
w/ photo-z
w/o photo-z
s81.0
from Gaztanaga, Cabre et al.
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DES Type Ia Supernovae

• Repeat observations of 40 deg2 , using 10 of
  survey time
• 1900 well-measured SN Ia
• lightcurves, 0.25 lt z lt 0.75
• Larger sample, improved z-band response compared
  to ESSENCE, SNLS address issues they raise
• Use a combination of photometric redshifts and
  spectroscopic redshifts (25)
• Develop supernova photo-z and color typing
  techniques better host galaxy photo-zs via
  stacking of repeat images

SDSS
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DES Photometric Redshifts

• Galaxies 68 photo-z scatter lt 0.1 using optimal
  neural network or nearest-neighbor polynomial
  methods

• Clusters robust photo-zs to redshifts 1.3,
  with 68 scatter of 0.02 or less

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DES Photometric Redshifts

• Accurate photo-z errors computed using
  nearest-neighbor error estimator
• Large completed and ongoing redshift surveys
  (SDSS, 2dFGRS, VVDS, DEEP2, ) will provide
  250,000 spectroscopic redshifts to DES depths
  for accurate photo-z calibrations
• Pursuing adding VISTA near-IR data to reduce
  photo-z errors at z gt 1 by factor of 2 to enhance
  science reach
• Actively working to
• Optimize photo-zs
• Understand photo-z errors
• Improve mock galaxy and cluster catalogs
• Optimize filter bandpasses
• Derive photo-z requirements set by cosmological
  parameter analyses

Normalized photo-z error distribution and
best-fit gaussian
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Example DES Photo-z Requirements

• Supernovae robust to DES photo-z error, given
  existing lower-z SDSS spectro-z supernova sample

• Weak lensing tomography want uncertainty in
  photo-z bias and scatter at the 10-3 level

from Z. Ma
from D. Huterer
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DES Forecasts Power of Multiple Techniques
Assumptions Clusters ?80.75, zmax1.5, WL
mass calibration (no clustering) BAO
lmax300 WL lmax1000 (no bispectrum
gal-mass included in combined) Statisticalphoto-
z systematic errors 0.002 only Spatial
curvature, galaxy bias marginalized Planck CMB
prior
w(z) w0wa(1a) 68 CL

• geometric
• growth

Clusters if ?80.9
geometric
Ma, Weller, Huterer, et al.
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Summary

• DES will measure dark energy using 4
  complementary probes (clusters, weak lensing,
  BAO, supernovae), using a 5000 deg2 griz survey
  (to 24th mag) with well-calibrated photometry and
  photo-zs
• New 3 deg2 DECam mosaic camera provides order of
  magnitude improvement in survey power over
  current CTIO Mosaic II camera
• The DES plans to start observing in late 2009,
  assuming DOE project approval
• The DES will serve as a valuable legacy data set
  for cosmology and astrophysics studies for the
  community
• DES is in unique international position to
  synergize with SPT and VISTA on DETF Stage III
  time scale precursor to more ambitious Stage IV
  projects like LSST and JDEM