Dark Energy Survey

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Dark Energy Survey

• The DES CollaborationJosh Frieman, Ofer Lahav, JW

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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, A. Kravtsov, E. Sheldon, R.
Wechsler Lawrence Berkeley National Lab G.
Aldering, N. Roe, C. Bebek, M. Levi, S.
Perlmutter NOAO/CTIO T. Abbott, C. Miller, C.
Smith, N. Suntzeff, A. Walker Institut d'Estudis
Espacials de Catalunya F. Castander, P. Fosalba,
E. Gaztañaga, J. Miralda-Escude Institut de
Fisica d'Altes Energies E. Fernández, M.
Martínez University College London O. Lahav, P.
Doel, M. Barlow, S. Bridle, S. Viti, S. Warwick,
J. Weller University of Cambridge G.
Efstathiou, R. McMahon, W. Sutherland University
of Edinburgh J. Peacock University of
Portsmouth R. Nichol University of Michigan R.
Bernstein, B. Bigelow, M. Campbell, A. Evrard,
D. Gerdes, T. McKay, M. Schubnell, G. Tarle, M.
Tecchio
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Dark Energy Stress Energy vs. Modified Gravity

• Stress-Energy G?? 8?G T??(matter)
  T??(dark energy)
• Gravity G?? f(g??) 8?G
  T??(matter)
• Key Experimental Questions
• Is DE observationally distinguishable from a
  cosmological
• constant, for which T?? (vacuum)
  ?g??/8?G?
• To decide, measure w what precision is
  needed?
• Can we distinguish between gravity and
  stress-energy?
• If w ? ?1, it likely evolves how well can/must
  we measure
• dw/da to make progress in fundamental
  physics?

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Probing Dark Energy with the Expansion History of
the Universe
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The Dark Energy Survey

• Study Dark Energy using
• 4 complementary techniques
• Cluster counts clustering
• Weak lensing
• Galaxy angular clustering
• SNe Ia distances
• Two multiband surveys
• 5000 deg2 g, r, i, z
• 40 deg2 repeat (SNe)
• Build new 3 deg2 camera
• Construction 2005-2009
• Survey 2009-2014 (525 nights)

Blanco 4-meter at CTIO
in systematics in cosmological parameter
degeneracies geometricgrowth test Dark Energy
vs. Gravity
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The DES Telescope

• NOAO/CTIO 4m Blanco telescope
• 1970 era, equatorial mount
• An existing, working telescope
• On-going studies finite element
• analysis, laser metrology, PSF pattern
  modeling
• Solid primary mirror
• 50cm thick Cervit, 15 tons
• Mechanical mirror support system
• radial purely mechanical
• axial 3 load cell hard points controllable
  support cells
• Primary cage
• DES will replace entire cage
• will have radial (alignment) movement
• Cerro Tololo
• site delivers median 0.65 Sept-Feb
• current Mosaic IItelescope delivers median 0.9
  Sept-Feb

3 Hard Points
Abbott, Walker, Peoples, Bernstein...
24 Radial Supports
33 Pressure Pads
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Dark Energy Survey Instrument
3.5 meters
Camera
1.5 meters
Scroll Shutter
Filters
Optical Lenses
New Prime Focus Cage, Camera, and Corrector for
the Blanco 4m Telescope 500 Megapixels,
0.27/pixel Project cost 20M
(incl. labor)
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Photometric Redshifts
Measure relative flux in four filters
griz track the 4000 A break Estimate
individual galaxy redshifts with accuracy
?(z) 0.1 (0.02 for clusters) This is
sufficient for Dark Energy probes (biases
?) Note good detector response in z
band filter needed to reach z1.3

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Seeing Issues
Seeing affects the number of galaxy images
usable for lensing

• Seeing is due to intrinsic PSF, telescope
  flexure, atmospheric turbulence the dome,
• Recent records for medians
• _at_ CTIO site 0.67 arcsec during Sep-Feb
• _at_ Blanco Mosaic II 0.9 arcsec
• Efforts to reduce it!

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Improved Optical Image Quality of DECAM vs.
Mosaic II

• Focus and wavefront sensor chips actively
  correct focus and collimation
• New optical corrector designed to deliver good
  image quality
• over FOV and wont be cracked
• Reduce power dissipation in vicinity of camera
• Precision focal plane alignment
• Model and track PSF vs. focal plane position,
  zenith angle (refraction),
• defocus, decollimation
• Typical object will be imaged 24 times in riz
  and enough
• survey time to use best conditions for WL
• 
  Gladders, Kent

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DES Area and Depth Synergy with South Pole
Telescope

• South Pole Telescope
• 4000 sq. deg. survey
• Detect 20,000 clusters
• through Sunyaev-Zeldovich
• effect
• Dark Energy Survey
• measure photometric
• redshifts for these clusters
• to z 1-1.3 griz 24

Galactic Dust Map
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10m South Pole Telescope (SPT)and 1000 Element
Bolometer Array

• Low noise, precision telescope
• 1.0 arcminute
• 3 levels of shielding
• 1 m radius on primary
• inner moving shields
• outer fixed shields

SZE and CMB Anisotropy - 4000 sq deg SZE
survey - deep CMB anisotropy fields - deep
CMB Polarization fields
People Carlstrom (UC) Holzapfel (UCB) Lee
(UCB,LBNL) Leitch (UC) Meyer (UC) Mohr (U
Illinois)Padin (UC) Pryke (UC) Ruhl
(CWRU) Spieler (LBNL) Stark (CfA)
1000 Element Bolometer Array - 3 to 4
interchangeable bands (90) 150, 250 270
GHz
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Cluster Redshift Distribution and Dark Energy
Constraints

• Raising w at fixed WDE
• ? decreases volume surveyed

? decreases growth rate of density
perturbations
Mohr
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Cosmology with Clusters

• Requirements
• Quantitative understanding of the formation of
  dark matter halos in an expanding universe
• Clean way of selecting a large number of massive
  dark matter halos (galaxy clusters) over a range
  of redshifts
• Redshift estimates for each cluster (photo-zs
  adequate)
• Observables that can be used as mass estimates at
  all redshifts

Jenkins, et al
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SZE vs. Cluster Mass Simulations
Integrated SZE flux decrement insensitive to gas
dynamics in the cluster core
Motl, et al
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Flux decrement vs. mass and redshift
Nagai - astro-ph/0512208 11 clusters ART
(Kravtsov)
shifted for clarity
blue star formation, metal enrichment and
thermal feedback due to the supernovae type II
and type Ia, self-consistent advection of metals,
metallicity dependent radiative cooling and UV
heating due to cosmological ionizing background
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DES Cluster Photometric Redshift Simulations
?(z)0.02 to z1.3
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Self-calibration with Clustering
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wa
-1
Hu
Lima and Hu
See also Battye and Weller, Majumdar Mohr
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Mapping the Mass in a Cluster of Galaxies via
Weak Gravitational Lensing (no arcs) Abell
3667 CTIO 4-m image Joffre, etal
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Calibration of the Mass - Temperature Relation
with Weak Lensing
(Dodelson Weller, in preparation)
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Background sources
Overdensities
Observer

• Statistical measure of shear pattern, 1
  distortion.
• Radial distances, r(z), depends on geometry of
  Universe.
• Dark Matter pattern growth depends on
  cosmological parameters.

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Lensing Tomography
zl1
zl2
z1
lensing mass
z2

• Shear at z1 and z2 given by integral of growth
  function distances over lensing mass
  distribution.

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DES Weak Lensing Tomography

• Measure shapes for 300 million
• source galaxies with ?z? 0.7
• Shear-shear galaxy-shear
• correlations probe distances
• growth rate of perturbations
• Requirements Sky area, depth,
• photo-zs, image quality stability

Huterer
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Galaxy Photo-z Simulations
DES griz filters
10? Limiting Magnitudes g 24.6 r 24.1
i 24.0 z 23.9 2 photometric
calibration error added in quadrature ?(z)0.1
to z1.3
Cunha, Lima, Oyaizu, Lin, Frieman, Collister,
Lahav
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Galaxy Photo-z Simulations
DES VISTA grizYJHKs filters
10? Limiting Magnitudes Y 22.45 J 22.15
H 21.65 Ks 21.15 (15 min exposures) ?(z)
0.07
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Impact of Uncertainty in Photo-z Error
Distribution on w
Spectroscopic Training Set needed to measure
photo-z error distribution to required
accuracy N 50,000 - 100,000
Ma, Hu, Huterer (2005)
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DES Supernovae
?z0.1 bins assumed

• Repeat observations of 40 deg2 , 10 of survey
  time
• 1900 well-measured riz SN Ia
• lightcurves, 0.25 lt z lt 0.75

SN constraints orthogonal to the other methods
Huterer
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Forecast DES Constraints on w

• Key Priors
• Constant w, spatially flat,
• power-law, adiabatic, Gaussian
• initial fluctuations,w/ CDM,
• massless neutrinos
• Marginalize over 3-parameter
• SZ(M) with no scatter
• 5 halo model bias parameters
• per photo-z bin
• WL llt1000
• SN sys. error floor, ?(m)0.25,
• 300 low-z SNe to anchor
• Hubble diagram

Flaugher, Walker, Abbott...
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Dark Energy 2009-2014

• DESSPT next step in dark energy
  measurements
• Will measure constant w to 0.020.1 statistical
  accuracy using multiple complementary probes,
  and begin to constrain dw/dz
• Survey strategy delivers substantial DE science
  after 2 years
• Scientific and technical precursor to the more
  ambitious and costly Dark Energy projects to
  follow LST and JDEM
• DES in unique position to synergize with SPT on
  this timescale
• accuracy on each probe separately,
  with Planck priors