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The Dark Energy Survey

John Peoples

Adapted from the P5 presentations byJosh Frieman andBrenna Flaugher

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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

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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

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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

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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)?

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• 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

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• 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)

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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)

• 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

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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

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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

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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

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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

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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

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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

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•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

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III. Baryon Acoustic Oscillations (BAO) in the CMB

• Characteristic angular scale set by sound horizon at recombination: standard ruler (geometric probe).

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Baryon Acoustic Oscillations: CMB & Galaxies

CMBAngularPowerSpectrum

SDSS galaxycorrelation function

Acoustic series in P(k) becomes a single peak in (r)

Bennett, etal

Eisenstein etal

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BAO in DES: Galaxy Angular Power Spectrum

Probe substantially larger volume and redshift range than SDSS

Wiggles due to BAO

Blake & BridleFosalba & Gaztanaga

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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

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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

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• 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

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From Scientific Goals to Science Quality Data

The Camera, the telescope and data management

Brenna Flaugher

DECam Project Manager

Fermilab

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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

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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

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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

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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

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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!

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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

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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

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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

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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

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• 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

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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

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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

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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

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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.

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arcsec

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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.

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• 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

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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

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This grid-based, modular and flexible data management system was deployed and tested in Data Challenge 1 (Oct ‘05-Jan ‘06)

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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

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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)

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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

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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

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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)

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DECam at CTIO

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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

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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%

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Side view

•

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Front view

•

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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

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Supernovae and photo-z errors

Huterer

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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

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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

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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