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1
The Dark Energy Survey
John Peoples
Adapted from the P5 presentations byJosh Frieman andBrenna Flaugher
2
The DES CollaborationFermilab: 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. WesterUniversity of Illinois at Urbana-Champaign: C. Beldica, R. Brunner, I. Karliner, J. Mohr, R. Plante, P. Ricker, M. Selen, J. ThalerUniversity of Chicago: J. Carlstrom, S. Dodelson, J. Frieman, M. Gladders, W. Hu, S. Kent, R. Kessler, E. Sheldon, R. WechslerLawrence Berkeley National Lab: N. Roe, C. Bebek, M. Levi, S. PerlmutterUniversity of Michigan: R. Bernstein, B. Bigelow, M. Campbell, D. Gerdes, A. Evrard, W. Lorenzon, T. McKay, M. Schubnell, G. Tarle, M. TecchioNOAO/CTIO: T. Abbott, C. Miller, C. Smith, N. Suntzeff, A. WalkerCSIC/Institut d'Estudis Espacials de Catalunya (Barcelona): F. Castander, P. Fosalba, E. Gaztañaga, J. Miralda-EscudeInstitut de Fisica d'Altes Energies (Barcelona): E. Fernández, M. MartínezCIEMAT (Madrid): C. Mana, M. Molla, E. Sanchez, J. Garcia-BellidoUniversity 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. PercivalUniversity of Sussex: A. Liddle, K. Romer
plus students
3
The Dark Energy Survey• Study Dark Energy using 4 complementary* techniques: I. Cluster Counts II. Weak Lensing III. Baryon Acoustic Oscillations IV. Supernovae
• Two multiband surveys: 5000 deg2 g, r, i, z 40 deg2 repeat (SNe)
• Build new 3 deg2 camera and Data management sytem Survey 2009-2015 (525 nights) Response to NOAO AO
Blanco 4-meter at CTIO
*in systematics & in cosmological parameter degeneracies*geometric+structure growth: test Dark Energy vs. Gravity
4
Dark Energy and the Accelerating Universe
Brightness of distant Type Ia supernovae, along with CMB and galaxy clustering data, indicates the expansion of the Universe is accelerating, not decelerating.
This requires either a new form of stress-energy with negative effective pressure or a breakdown of General Relativity at large distances:
DARK ENERGY
Characterize by its effective equation of state: w = p/<1/3and its relative contribution to the present density of the Universe: DE
Special case: cosmological constant: w = 1
5
What is the Nature of the Dark Energy?
Stress-Energy: G = 8G [T(matter) + T(dark energy)]
Gravity: G + f(g) = 8G T(matter)
Key Experimental Questions:
• Is DE observationally distinguishable from a cosmological constant, for which T (vacuum) = g/3, i.e., w =—1? • Can we distinguish between gravity and stress-energy? Combine geometric with structure-growth probes • Does dark energy evolve: w=w(z)?
6
• Probe dark energy through the history of the expansion rate:
H2(z) = H20 [M (1+z) 3 + DE (1+z) 3 (1+w) ] (flat Universe)
matter dark energy
• Comoving distance: Weak Lensing r(z) = dz/H(z)• Standard Candles: Supernovae dL(z) = (1+z) r(z)• Standard Rulers: Baryon Oscillations dA(z) = (1+z)1 r(z)• Standard Population: Clusters dV/dzd = r2(z)/H(z)• The rate of growth of structure also det’d by H(z)
Probing Dark Energy
7
• Probe dark energy through the history of the expansion rate:
and the growth of large-scale structure:
• Parametrize DE Evolution:
• Geometric tests:• Comoving distance Weak Lensing • Standard Candles Supernovae • Standard Rulers Baryon Oscillations • Standard Population Clusters
Probing Dark Energy
H 2(z)
H02 m (1 z)3 DE exp 3 (1 w(z))d ln(1 z) 1 m DE 1 z 2
a
w(z)w0 wa (1 a) ...
r(z)Fdz
H z
dL z 1 z r(z)
dA z 1 z 1r(z)
dV
dzdr2(z)
H(z)
8
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)
• Precision is sufficient for Dark Energy probes, provided error distributions well measured.
• Note: good detector response in z band filter needed to reach z>1
Elliptical galaxy spectrum
DESgriz filters10 Limiting Magnitudes g 24.6 r 24.1 i 24.0 z 23.9
+2% photometric calibrationerror added in quadrature
Key: Photo-z systematic errors under control using existing spectroscopic training sets to DES photometric depth
Galaxy Photo-z Simulations
+VHS JK
Improved Photo-z & Error Estimates and robust methods of outlier rejection
DES
Cunha, etal
DES + VHS on
ESO VISTA 4-m
enhances science reach
10
I. Clusters and Dark Energy
MohrVolume Growth(geometry)
Number of clusters above observable mass threshold
Dark Energy equation of state
dN(z)
dzd
dV
dz dn z
•Requirements1.Understand formation of dark matter halos 2.Cleanly select massive dark matter halos (galaxy clusters) over a range of redshifts 3.Redshift estimates for each cluster 4.Observable proxy that can be used as cluster mass estimate: O =g(M)
Primary systematic: Uncertainty in bias & scatter of mass-observable relation
11
Cluster Cosmology with DES
• 3 Techniques for Cluster Selection and Mass Estimation:• Optical galaxy concentration• Weak Lensing • Sunyaev-Zel’dovich effect (SZE)
• Cross-compare these techniques to reduce systematic errors
• Additional cross-checks:
shape of mass function; cluster
correlations
12
10-m South Pole Telescope (SPT)
SPT will carry out 4000 sq. deg. SZE Survey
PI: J. Carlstrom (U. Chicago)
NSF-OPP funded & scheduled for Nov 2006 deploymentDOE (LBNL) funding of readout development
Sunyaev-Zel’dovich effect- Compton upscattering of CMB photons by hot gas in clusters- nearly independent of redshift: - can probe to high redshift - need ancillary redshift measurement
Dec 2005
13
SZE vs. Cluster Mass: Progress in Realistic Simulations
Motl, etalIntegrated SZE flux decrement depends only on cluster mass: insensitive to details of gas dynamics/galaxy formation in the cluster core robust scaling relations
Nagai
SZE
flu
x
Adiabatic∆ Cooling+Star Formation
SPT
Obs
erva
ble
Kravtsov
Future:SCIDACproposal
small (~10%) scatter
14Argonne 25 Oct 2006
Gravitational Lensing by Clusters
Weak Lensing of Faint Galaxies: distortion of shapes
BackgroundSourceshape
ForegroundCluster
Weak Lensing of Faint Galaxies: distortion of shapes
BackgroundSourceshape
Note: the effect has been greatly exaggerated here
ForegroundCluster
Lensing of real (elliptically shaped) galaxies
Co-add signal around a number of Clusters
BackgroundSourceshape
18
Statistical Weak Lensing CalibratesCluster Mass vs. Observable Relation
Cluster Massvs. Number of galaxies they contain
For DES, will use this to independently calibrate SZE vs. Mass
Johnston, Sheldon, etal, in preparation
Statistical Lensing eliminates projection effectsof individual cluster massestimates
Johnston, etalastro-ph/0507467
SDSS DataPreliminaryz<0.3
19
Observer
Dark matter halos
Background sources
Statistical measure of shear pattern, ~1% distortion Radial distances depend on geometry of Universe Foreground mass distribution depends on growth of structure
II. Weak Lensing: Cosmic Shear
20
•Cosmic Shear Angular Power Spectrum in 4 Photo-z Slices
•Shapes of ~300 million galaxies median redshift z = 0.7
•Primary Systematics: photo-z’s, PSF anisotropy, shear calibration
Weak Lensing Tomography
DES WL forecasts conservatively assume 0.9” PSF = median delivered to existing Blanco camera: DES should do better & be more stable (see Brenna’s talk)
Huterer
Statistical errorsshown
21
III. Baryon Acoustic Oscillations (BAO) in the CMB
• Characteristic angular scale set by sound horizon at recombination: standard ruler (geometric probe).
22
Baryon Acoustic Oscillations: CMB & Galaxies
CMBAngularPowerSpectrum
SDSS galaxycorrelation function
Acoustic series in P(k) becomes a single peak in (r)
Bennett, etal
Eisenstein etal
23
BAO in DES: Galaxy Angular Power Spectrum
Probe substantially larger volume and redshift range than SDSS
Wiggles due to BAO
Blake & BridleFosalba & Gaztanaga
24
IV. Supernovae
• Geometric Probe of Dark Energy
• Repeat observations of 40 deg2 , using 10% of survey time
• ~1900 well-measured SN Ia lightcurves, 0.25 < z < 0.75
• Larger sample, improved z-band response compared to ESSENCE, SNLS; address issues they raise
• Improved photometric precision via in-situ photometric response measurements
SDSS
25
DES Forecasts: Power of Multiple Techniques
Ma, Weller, Huterer, etal
Assumptions:Clusters: 8=0.75, zmax=1.5,WL mass calibration(no clustering)
BAO: lmax=300WL: lmax=1000(no bispectrum)
Statistical+photo-z systematic errors only
Spatial curvature, galaxy biasmarginalized
Planck CMB prior
w(z) =w0+wa(1–a) 68% CL
geometric
geometric+growth
Clustersif 8=0.9
26
• Will measure Dark Energy using multiple complementary probes, developing these techniques and exploring their systematic error floors
• Survey strategy delivers substantial DE science after 2 years
• Relatively modest, low-risk, near-term project with high discovery potential
• Scientific and technical precursor to the more ambitious Stage IV Dark Energy projects to follow: LSST and JDEM
• DES in unique international position to synergize with SPT and VISTA on the DETF Stage III timescale (PanSTARRS is in the Northern hemisphere; cannot be done with existing facilities in the South)
DES and a Dark Energy Program
27
From Scientific Goals to Science Quality Data
The Camera, the telescope and data management
Brenna Flaugher
DECam Project Manager
Fermilab
28
DES Science and Technical Requirements
• 5000 deg2 of the So. Galactic Cap in 525 nights (5 yrs)
• photometric-redshifts to z=1.3 with dz < 0.02.
• A small and stable point spread function (PSF) < 0.9'' FWHM median
• A large camera, on the Blanco 4m– 3 deg2 camera with ≥ 2.2 deg FOV
• Data Management system– 300GB/night, automated processing– Publicly available data archive after 1 yr
• Filters, CCDs, Read noise– SDSS g,r,i,z filters; 400 - 1100nm– QE > 50% in the z band (825-1100nm)– Read noise <10 e-
• Optical Corrector with excellent images– Pixel size <0.3” /pixel– < 0.4” FWHM in the i and z bands
Science Requirements Technical Requirements
29
The DES Instrument: DECam
3556 mm
1575 mm
Hexapod
Optical Lenses
F8 Mirror
CCDRead out
DECam will replace the prime focus cage on the Blanco
Filters Shutter
Prime Focus Instrument-in optical path-space and thermal constraints
30
DES CCDsLBNL Design: fully depleted 2kx4k CCDs
– QE> 50% at 1000 nm, 250 microns thick– 15 m pixels, 0.27”/pixel– readout 250 kpix/sec, readout time ~17sec
DECam / Mosaic II QE comparison
0
10
20
30
40
50
60
70
80
90
100
300 400 500 600 700 800 900 1000 1100
Wavelength (nm)
QE, LBNL (%)QE, SITe (%)
LBNL CCDs in use on WIYN telescope. From S. Holland et al, LBNL-49992 IEEE Trans. Elec. Dev. Vol.50, No 1, 225-338, Jan. 2003
LBNL CCDs are much more efficient than the SITE CCDs in Mosaic II at high wavelengths
To reach redshifts of ~1.3 DES will spend 46% of survey time in z –band
DES CCD design has already been used on telescopes in small numbers (3)
DES is the 1st
production quantity
application for LBNL
CCDs
z band
31
CCD Fabrication and Packaging Business model developed by LBNL:• Foundry delivers partially processed wafers to LBNL
(~650 microns thick)
• LBNL finishes wafers (250 microns thick), tests, dices (production rate 5 wafers/month
• FNAL builds up the CCD packages and tests CCD – will match CCD delivery rate
Preconceptual R&D: • 44 Eng. grade 2kx4k CCDs in hand, plus 20 in Dec• used to develop focal plane packages, characterize
CCD performance, test CCD readout electronics
FY07: establish CCD processing and packaging yield
– preliminary est. 25% yield (SNAP devices)– implies 18 months and $1.6M for 70 good devices– CCD yield is a cost and schedule driver
DES Wafers – June 2005!
32
Front End Electronics: CCD Readout
• FNAL, Barcelona, Madrid, UIUC• Spanish consortium is participating in
the FEE development and has been funded to provide production FEE.
• Status:– UIUC has purchased prototype
readout systems for testing– have already achieved 6.5e noise
at ~200 kpix/sec, – have a design that fits in 3 temp.
controlled crates in PF cage– Test of readout of multiple CCDs is
in progress
Part of Fermilab Team in the testing lab
LN2 DewarsReadout racks
Filter and shutter controls
3 operational CCDtesting setups
33
Camera Vessel Prototype
10 slot thermally controlled crate for CCD readout electronics
Cryo and Vacuum controls
Focal plane
Feed-through board for CCD signals
Full size prototype was built by U. Chicago and it being used to test multi-CCD readout
34
Survey Image System Process Integration (SISPI)
CTIO will upgrade the Telescope Control System (TCS)
Data Management (DM): U. Illinois-Astro/NCSA
U Illinois-HEP (J. Thaler) is leading the SISPI development- similar to HEP-DAQ systems
35
Optical Corrector Design• Preliminary Design complete (UMich, FNAL, UCL)
– Image quality fwhm: ~ 0.33” (<0.4” required)
• March 2006, PPARC Council announced that it “will seek participation in DES”
– The UK Consortium funded by PPARC to lead the procurement of the optics subject to US approval
– 1.47 M pound proposal to cover cost of polishing, mounting, and alignment of the lenses in the barrel
– P. Doel at U. College London Optical Science Lab will manage the procurement and fabrication
• Additional UK funding ($0.4M ) available through Portsmouth (SRIF3): ~60% of the blanks
• US Universities will fund the remainder.• Procurement of the optics is ~2 years • CRITICAL PATH
filter
Dewarwindow
C1 has 940 mmdiameter
C2C3
C4
5 elements, fused silica
36
• U. Michigan will– handle procurement and testing of
the filters– match SDSS – g,r,i,z and
introduce a well defined cut-off at high wavelength
– design and fabricate or procure a combined filter changer and shutter
DES FiltersDark Energy Camera Filters
0.0000
10.0000
20.0000
30.0000
40.0000
50.0000
60.0000
70.0000
80.0000
90.0000
100.0000
300 400 500 600 700 800 900 1000 1100 1200
Wavelength
%Tra
nsm
itta
nce
925nm 775nm 635nm 475nm
Filter changer will be a cartridge system similar to PanStarrs design
37
The Blanco Telescope• Commissioned in 1974 primary mirror quality
(D80 = 0.25 arcsec) defined state-of-the-art.
• The critical observations for the discovery of Dark Energy were made with this telescope.
• Extensive set of improvements in the 90’s
– Primary mirror active support system (active optics), to replace the passive support system.
– Environmental improvements, e.g. windows in the dome to promote air flow, removal of heat sources.
THE SITE: - October to January - weather improving, nights get shorter (av. 6.8 hr/night useable)- Mean site seeing at 5m above ground = 0.65 arcsec
38
DECam & CTIO
• High-quality primary, D80 at manufacture: 0.25”
• Active Optics
– 33-pad system, LUT driven, updated every few months
– DECam will provide in-line updates (via “donut”) possibly allowing us to close the loop during observations
39
DECam & CTIO
• Primary mirror repositioned 2.3mm in z-direction
• Primary mirror is now centered in cell– Coma was dominant and variable, is now the third
most significant aberration and stable.
0
20
40
60
80
100
120
140
160
180
0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4
arcsec
Fre
qu
ency
Image Quality obtained by the SuperMacho program, 2005B, airmass corrected, VR filter. Dates: 2005-09-05 to 2005-12-31, Blue: pre-shutdown, red: post-shutdown, approx equal number (~580) exposures each.
40
• 2004 Level 0 Image Simulations → DM Challenge 0: Done!– Reformatted SDSS data used to simulate DES images
• 2005-06 Level 1 Catalog &Image Sim. → DM Chal. 1: Done!– 500 sq. deg. catalog; 500 GB of images; FNAL and UChicago computing used
• 2006-07 Level 2 Catalog and Image Sim. In progress– 5000 sq. deg. catalog; 5 TB of images– FermiGrid & MareNostrum SuperComputer (Barcelona)– Higher resolution N-body simulation, more realistic galaxy properties, and more
sophisticated atmosphere and instrument models (noise, ghosts)– Recover input cosmology from catalogs using 4 DES key project methods
• 2007-8 Level 3 Catalog and Image Simulations– Suite of full-DES catalogs (i.e., different input cosmologies)– Synergy with DOE SciDAC proposal (with many DES collaborators) to produce
large cosmological simulations for dark energy studies– 1 year of DES imaging data– Recovery of input cosmologies from catalogs and images– Stress test of full data processing system
DES Simulations Feed DM Challenges
41
DES Data Management Project• U. Illinois and NCSA lead the DM project
– Joe Mohr (U. Illinois) is the project leader– Cristina Beldica (NCSA) is the project manager
• 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
U Illinois/NCSA DES DM Team
42
This grid-based, modular and flexible data management system was deployed and tested in Data Challenge 1 (Oct ‘05-Jan ‘06)
43
DM Schedule and Status
• Pursuing iterative development strategy ‘04-’09
– Yearly data challenges Oct-Jan ‘05-’08– Development targets full delivery in 2009
DC1: base level system in place DC2: data quality, stress test DC3: deploy and test outside NCSA DC4: final validation and stress test
• Data Challenge 1 Results (Oct 1 ‘05-Jan 31 ‘06)
– DM system deployed and tested– Automated reduction (500GB raw reduced
into 5TB)– Catalogued and calibrated 50 million objects– Confirmed photometry and astrometry
Reduced, pseudo-colorDC1 Image
44
DECam critical paths: CCDs & Optics
CCDs:• LBNL can deliver CCDs at a rate of 20/month after 3 month startup• We need 70 CCDs for the FP including spares• Preliminary yield estimate of 25% implies ~18 months • Construction start of Jan 08 implies last CCD is finished July ’10• Install last CCD and test full camera ~ 2 months• Ready to ship to Chile ~ Fall ’10
Optics:• Order glass blanks and seek tenders for finishing lenses (Feb 07) • Assembly and alignment into corrector ~ 6 months• Ready to ship to Chile ~ 3 yrs after procurement begins (Feb ’10)
45
DES Project Approval Status Collaboration formed Dec. 2003 June 2004 Fermilab Directors Review #1 July 2004: Fermilab Director gives DES Stage 1 approval
Collaboration can submit a proposal to NOAO with Fermilab support Aug 2004: NOAO Director accepts DES proposal for partnership
525 nights of CTIO 4m time in return for new instrument and archive May 2005: Science working groups form
submit white paper (astro-ph/0510346) to Dark Energy Task Force May 2006: DETF recommends a Stage III experiment like DES July 2006: P5 recommends that DES start construction in FY2008
and HEPAP endorses the P5 report and sends it to DOE and NSF July 2006: Fermilab Director’s Review #2 October 2006: NSF and DOE request a plan describing the entire
experiment “end-to-end” that they will review jointly
46
DECam Project Status and Forecast
FY05 and 06 were generic R&D years CCDs: set up production with LBNL, develop CCD test
systems, & demonstrate packaging 25 wafers in FY2005 and FY2006 Optics: finalized design, firm cost estimate developed DECam and DESDM conceptual design completed
FY07 project R&D `CCD yield determination and system tests Front end electronic board development and systems tests Data Challenge 3
FY08, FY 09 & FY10 are construction years Winter 2010: ship instrument to Chile Fall 2010: start survey
47
Conclusions
DES provides the next logical step in both
technology and science– Builds on existing technology and infrastructure, and capitalizes on
collaboration’s experience with large DAQ systems, silicon vertex detectors, and data handling
– 3 deg2 camera: x7 larger area and x7 faster readout than existing Mosaic camera on the Blanco
– 1PB total processed images available to the public; data released 1 year after images taken
– Development and implementation of data analysis techniques for photo-z’s, cluster masses, weak lensing, baryon oscillations, and supernovae are the next steps toward the science of the Stage IV projects of the future (LSST, SNAP)
48
DECam at CTIO
49
50
extras
51Argonne 25 Oct 2006
Evolution of Structure
Robustness of the paradigm recommends its use as a Dark Energy probe
Price: additional cosmological and structure formation parameters
Bonus: additional structure formationParameters
Methods: WL, Clusters
52
CCD Requirements
LBNL CCD performance DECam requirements/
Reference Design Pixel array 2048 4096 pixels 2048 4096 pixels Pixel size 15 m 15 m 15 m 15 m (nominal)
<QE (400-700 nm)> ~70% >60% <QE (700-900 nm)> ~90% >80%
<QE (900-1000 nm)> ~60% >50% at 1000 nm Full well capacity 170,000 e- >130,000 e-
Dark current 2 e-/hr/pixel at –150oC <~25 e-/hr/pixel Persistence Erase mechanism Erase mechanism Read noise 7 e- @ 250 kpixel/s < 10 e-
Charge Transfer Inefficiency < 10-6 <10-5 Charge diffusion 8 m < 10 m
Linearity Better than 1% 1%
53
Side view
•
54
Front view
•
55
Isometric view camera end
•
Photo-z Error Distributions & Error Estimates
Robustly Reducing Catastrophic Errors
Remove 10% of objects via color cuts 30% improvement
Original 10% Cut
58
Supernovae and photo-z errors
Huterer
59
Improving Corrections for Anisotropic PSF
• Whisker plots for three BTC camera exposures; ~10% ellipticity
• Left and right are most extreme variations, middle is more typical.
• Correlated variation in the different exposures: PCA analysis -->
can use stars in all the images: much better PSF interpolation
Focus too low Focus (roughly) correct Focus too high
Jarvis and Jain
60
PCA Analysis
• Remaining ellipticities are essentially uncorrelated.• Measurement error is the cause of the residual shapes.• 1st improvement: higher order polynomial means PSF accurate to smaller scales• 2nd: Much lower correlated residuals on all scales
Focus too low Focus (roughly) correct Focus too high
61
Reducing WL Shear Systematics
See Brenna’s talk for DECam+Blancohardwareimprovements that will reduce raw lensing systematics
Red: expected signal
Results from 75 sq. deg. WLSurvey with Mosaic II and BTCon the Blanco 4-mBernstein, etal
DES: comparable depth: source galaxies well resolved & bright:low-risk
(improved systematic)
(signal)
Shear systematics under control at level needed for DES
(old systematic)
Cosmic Shear