# Presentation: 594532

## The Dark Energy Survey 

***(DES)***

**Huan Lin**
**Experimental Astrophysics Group**
**Fermilab**
***On behalf of the Dark Energy Survey Collaboration***

## The Dark Energy Survey (DES)

**Proposal:**
**Perform a 5000 deg****2**** *****griz***** survey of the Southern Galactic Cap**
**Study dark energy using 4  complementary techniques: *****galaxy clusters, weak lensing, galaxy angular power spectrum, and Type Ia supernovae***
**New Instrument:**
**Large 3 deg****2**** mosaic CCD camera and optical corrector for the CTIO 4m Blanco telescope   **
**Construction 2005-2009**
**Survey: **
**30% of the telescope time from 2009-2013**
**Data released to public within a year of observations**

**Blanco 4m Telescope **
**at the Cerro-Tololo**
**Inter-American **
**Observatory (CTIO)**

## Basic Survey Parameters

**5000 deg****2**** Survey Area**
**4000 deg****2**** of overlap with South Pole Telescope (SPT) survey area**
**Also includes SDSS Southern Equatorial Stripe + deep galaxy redshift survey fields**
**Limiting Magnitudes**
**Galaxies: 10****σ *****griz***** = 24.6, 24.1, 24.3, 23.9**
**Point sources: ****5****σ *****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**

## The DES Instrument

**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 deg****2**** field of view**

## DES CCDs

**LBNL CCDs**
**High quantum efficiency in the red:  QE > 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**

## 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-Zel’dovich (SZ) data provides robust cluster masses**
**~30000 clusters in 4000 deg****2**** area of DES-SPT overlap**
**Multiple cluster mass estimators (SZ, optical luminosity, lensing) and cross-checks of sample selection effects**

- Majumdar & Mohr 2003
- Spergel et al 2003

## DES: Weak Lensing

**Measure shapes for ~300 million source galaxies**
**Average galaxy redshift ~0.7**
**Effective galaxy surface density of ~10 per arcmin****2 **
**Shear-shear and galaxy-shear correlations probe distances and growth rate of perturbations**
**Also provides independent calibration of cluster masses**

## DES: Angular Power Spectrum

**Angular power spectrum of 300 million galaxies over 5000 deg****2**
**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**

**Wayne Hu 2004**

## DES: Type Ia Supernovae

**Repeat observations of 40 deg****2****, 10% of survey time**
**~2000 well-measured SN Ia light curves, 0.25 < z < 0.75**
**Larger sample, improved z-band response compared to ESSENCE and CFHTLS**
**Combination of spectroscopic (~25%) and photometric redshifts**
**Develop color typing and SN photo-z’s (critical for LSST)**

## DES Photometric Redshifts

**Clusters:**** ****robust photo-z’s to redshifts ~1.3, with 68% scatter of 0.02 or less**
**Field galaxies:**** ****68% photo-z scatter of 0.07 using optimal “comparison” method**
**Large completed and ongoing redshift surveys (SDSS, 2dFGRS, VVDS, DEEP2) will provide ~250,000 redshifts for calibrating photo-z’s and characterizing error distributions in detail**
**Actively working to improve mock galaxy and cluster catalogs, understand photo-z errors, and derive photo-z requirements set by**** ****cosmological parameter analyses**

**DES cluster photo-z simulation**

##  DES Dark Energy Constraints

| Method/Prior | Uniform | WMAP | Planck |
| --- | --- | --- | --- |
| Galaxy Clusters:
  abundance
  w/ WL mass calibration | 0.13
0.09 | 0.10
0.08 | 0.04
0.02 |
| Weak Lensing:
  shear-shear (SS)
  galaxy-shear (GS) + galaxy-galaxy (GG)
  SS+GS+GG
  SS+bispectrum | 0.15
0.08
0.03
0.07 | 0.05
0.05
0.03
0.03 | 0.04
0.03
0.02
0.03 |
| Galaxy angular clustering | 0.36 | 0.20 | 0.11 |
| Supernovae Ia | 0.34 | 0.15 | 0.04 |

**Forecast statistical constraints on **
**constant equation of state parameter w models**
**(DES DETF white paper, astro-ph/0510346)**

**4  Dark Energy Techniques**
**Galaxy clusters**
**Weak lensing**
**Angular power spectrum**
**Type Ia supernovae**
**Statistical errors on constant w models typically ****σ****(w) = 0.05-0.1**
**Complementary methods**
**Constrain different combinations of cosmological parameters**
**Subject to different systematic errors**

## DES Project Status

**1****st**** Collaboration Meeting Dec. 2003**
**July 2004: Fermilab Director gives DES Stage 1 approval **
**Fermilab resources can be used for R&D**
**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**
**write Dark Energy Task Force white paper (astro-ph/0510346)**
**FY05 and 06 are R&D years **
**CCDs: establish yield, learn to test CCDs, demonstrate packaging**
**25 wafers in FY2005 and FY2006 **
**Optics: finalize design, develop firm cost estimate**
**order glass in FY2006, figure and polish in FY2007**
**FY07 and FY 08 are construction years**
**Jan 2009: ship instrument to Chile **
**Sept 2009: start survey**

## 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, E. Sheldon, R. Wechsler.   * Carnegie Observatories until summer 2006
**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, R. Bingham, S. Bridle, S. Viti, 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, A. Evrard, D. Gerdes, T. McKay

- 61 scientists at 12 institutions