1P5 – April 20, 2006

The Dark Energy Survey

Josh Frieman

White Papers submitted to Dark Energy Task Force:

astro-ph/0510346

Theoretical & Computational Challenges:astro-ph/0510194,5

2P5 – April 20, 2006

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

3P5 - April 20, 2006

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

4P5 – April 20, 2006

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

P5 – April 20, 2006

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

+VDES JK

Improved Photo-z & Error Estimates and robust methods of outlier rejection

DES

Cunha, etal

DES + VDES on

ESO VISTA 4-m

enhances science reach

6P5 – April 20, 2006

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

7P5 – April 20, 2006

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

8P5 – April 20, 2006

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

9P5 – April 20, 2006

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

10P5 – April 20, 2006

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

11P5 – April 20, 2006

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

12P5 – April 20, 2006

•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

13P5 - April 20, 2006

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

14P5 - April 20, 2006

III. Baryon Acoustic Oscillations (BAO) in the CMB

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

15P5 - April 20, 2006

Baryon Acoustic Oscillations: CMB & Galaxies

CMBAngularPowerSpectrum

SDSS galaxycorrelation function

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

Bennett, etal

Eisenstein etal

16P5 – April 20, 2006

BAO in DES: Galaxy Angular Power Spectrum

Probe substantially larger volume and redshift range than SDSS

Wiggles due to BAO

Blake & BridleFosalba & Gaztanaga

17P5 – April 20, 2006

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

18P5 – April 20, 2006

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

19P5 – April 20, 2006

• 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

20P5 – April 20, 2006

Extra Slides

P5 – April 20, 2006

Spectroscopic Redshift Training Sets for DES

Redshift SurveyNumber of Redshifts

Overlapping DES

Sloan Digital Sky Survey 70,000, r < 20

2dF Galaxy Redshift Survey

90,000, bJ<19.45

VIMOS VLT Deep Survey ~60,000, IAB<24

DEEP2 Redshift Survey ~30,000, RAB<24.1

Training Sets to the DES photometric depth in place (advantage of a `relatively’ shallow survey)

P5 – April 20, 2006

DES Cluster Photometric Redshift Simulations

DES:for clusters,(z) < 0.02 for z <1.3

DES+VDESgriz+JK on VISTA:extend photo-z’s toz~2(enhances, but not critical to, science goals)

P5 – April 20, 2006

Variance and Bias of Photo-z Estimates

Cunha etal

Variance Bias

P5 – April 20, 2006

Photo-z Error Distributions & Error Estimates

P5 – April 20, 2006

Robustly Reducing Catastrophic Errors

Remove 10% of objects via color cuts 30% improvement

Original 10% Cut

P5 – April 20, 2006

Clusters and Photo-z Systematics

27P5 – April 20, 2006

Weak Lensing & Photo-z Systematics

Ma

(w0)/(w0|pz fixed) (wa)/(wa|pz fixed)

28P5 – April 20, 2006

BAO & Photo-z Systematics

Ma

(w0)/(w0|pz fixed)

(wa)/(wa|pz fixed)

29P5 – April 20, 2006

Supernovae and photo-z errors

Huterer

30P5 - April 20, 2006

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 lowFocus (roughly) correctFocus too high

Jarvis and Jain

31P5 - April 20, 2006

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 lowFocus (roughly) correctFocus too high

32P5 – April 20, 2006

Image

Lensing ClusterSource

Tangential shear

33P5 – April 20, 2006

Statistical Weak Lensing by Galaxy Clusters

Mean

Tangential

Shear

Profile

in Optical

Richness

(Ngal) Bins

to 30 h-1Mpc

Sheldon,

Johnston, etal

SDSS preliminary

34P5 – April 20, 2006

Johnston, Sheldon, etalSDSS preliminary

Invert Mean Shear Profile to obtain Mean Mass Profile

Virial Mass

Vir

ial r

adiu

s

35P5 – April 20, 2006

Precision Cosmology with Clusters

• 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

Sensitivity to Mass Threshold

dN(z)

dzd c

H z dA2 1 z 2 dM

dn M,z dM

f M 0

Massthreshold

36P5 – April 20, 2006

Forecasts for Constant w Models(DE) (w)

37P5 – April 20, 2006

Forecasts with WMAP Priors(w0) (wa)