# Presentation: 499865

## The Dark Energy Survey 

***(DES)***

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

## The Dark Energy Survey (DES)

**Study Dark Energy using 4 complementary techniques:**
***Galaxy clusters***
***Weak lensing***
***Baryon acoustic oscillations***
***Type Ia supernovae***
**2 Multiband Surveys: **
**5000 deg****2**** *****griz***** survey of the Southern Galactic Cap**
**40 deg****2 ****repeated for supernovae**
**525 nights (2009-2015) on the CTIO 4m Blanco telescope**
**Build:**
**Large 3 deg****2**** mosaic CCD camera and optical corrector for the Blanco**
**Data management system**
**Response to NOAO AO**

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

## 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, R. Kessler, E. Sheldon, R. Wechsler
- Lawrence Berkeley National Lab: N. Roe, C. Bebek, M. Levi, S. Perlmutter
- University of Michigan: R. Bernstein, B. Bigelow, M. Campbell, D. Gerdes, A. Evrard, W. Lorenzon, T. McKay, M. Schubnell, G. Tarle, M. Tecchio
- NOAO/CTIO: T. Abbott, C. Miller, C. Smith, N. Suntzeff, A. Walker
- CSIC/Institut d'Estudis Espacials de Catalunya (Barcelona): F. Castander, P. Fosalba, E. Gaztañaga, J. Miralda-Escude
- Institut de Fisica d'Altes Energies (Barcelona): E. Fernández, M. Martínez
- CIEMAT (Madrid): C. Mana, M. Molla, E. Sanchez, J. Garcia-Bellido
- University 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. Percival
- University of Sussex: A. Liddle, K. Romer

- plus students

## 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 Dark Energy Camera (DECam)

**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**

- 3556 mm

- 1575 mm

- Hexapod

- Optical
- Lenses

- F8 Mirror

- CCD
- Read out

- Filters
- Shutter

## 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 CCD QE

- Current Mosaic II QE

## DES Data Management

**U. Illinois and NCSA lead the DM project**
**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**

## DES Simulations

**Yearly cycles of simulations provide data for development of data reduction pipelines and science analysis codes**
**Completed Level 1 Simulations**
**500 deg****2**** galaxy catalog**
**500 GB of science images;  shapelets-based**
**Ongoing Level 2 Simulations**
**5000 deg****2**** galaxy catalog**
**~5 TB of science images**
**Use collaboration computing resources, including FermiGrid and Barcelona Marenostrum supercomputer**
**Recovery of input cosmology from catalogs**
**Future Level 3 Simulations**
**Suite of full-DES catalogs**
**1 year of DES imaging data**
**Synergy with DOE SciDAC proposal to produce large cosmological simulations for dark energy studies**
**Recovery of input cosmologies from catalogs and images**

*gri* color composite of example Level 1 simulation image

- Parent N-body box for Level 2 catalog simulation

## 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 effect (SZE) data provides robust cluster masses**
**Tens of thousands of clusters in 4000 deg****2**** area of DES-SPT overlap**
**Multiple cluster mass estimators (optical richness, SZ, lensing) and cross-checks of sample selection effects**

- from J. Mohr

## Cluster Mass-Observable Calibration

**Simulations indicate robust cluster mass vs. SZE flux decrement relationship**

- Nagai, Motl, et al.

- SZE flux

****** ****Adiabatic**
**∆**** ****Cooling+Star**
**   ****Formation**

- small (~10%)
- scatter

- Johnston, Sheldon, et al., in preparation

- SDSS Data
- Preliminary
- z<0.3

**Lensing will be used to calibrate  cluster mass vs. optical richness relationship;  cf. SDSS**

## 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**

**from D. Huterer**

- cosmic shear angular power spectrum in 4 redshift bins

## DES: Weak Lensing

- Red: expected signal

- Results from 75 sq. deg. WL Survey with Mosaic II and BTC on the Blanco 4-m (Bernstein et al.)
- DES: comparable depth: source galaxies well
- resolved & bright: _low-risk_

- (improved systematic)

- (signal)

- (old systematic)

-  Cerro Tololo Image Quality Sept-Feb
-  site median PSF 0.65” FWHM
-  Prime Focus (PF) delivered median PSF 0.9” FWHM (used in all DES constraint forecasts)
-  DES/CTIO upgrades will stabilize the PSF and should improve the median FWHM:
-  DES
-  focus and alignment sensors on focal plane: generate focus and lateral alignment information with each image
-  active control of camera position: hexapods will provide focus and lateral adjustments of corrector + camera system
-  improved thermal environment: heat dissipation will be actively controlled
-  CTIO is upgrading the primary mirror radial supports to reduce mirror motions

## DES: Baryon Acoustic Oscillations

**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**

- SDSS galaxy
- correlation function

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

- Eisenstein et al.

## DES: ISW

- 8=1.0

- 8=0.9

- w/ photo-z

- w/o photo-z

- from Gaztanaga, Cabre et al.

##  DES: Type Ia Supernovae

- 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
- Use a combination of photometric redshifts and spectroscopic redshifts (~25%)
- Develop supernova photo-z and color typing techniques;  better host galaxy photo-z’s via stacking of repeat images

- SDSS

## DES Photometric Redshifts

**Galaxies:**** ****68% photo-z scatter < 0.1 using optimal neural network or nearest-neighbor polynomial methods**

**Clusters:**** ****robust photo-z’s to redshifts ~1.3, with 68% scatter of 0.02 or less**

## DES Photometric Redshifts

**Normalized photo-z error distribution and best-fit gaussian**

**Accurate photo-z errors computed using nearest-neighbor error estimator**
**Large completed and ongoing redshift surveys (SDSS, 2dFGRS, VVDS, DEEP2, ...) will provide ****~250,000 spectroscopic redshifts to DES depths ****for accurate photo-z calibrations**
**Pursuing adding VISTA near-IR data to reduce photo-z errors at z > 1 by factor of 2 to enhance science reach**
**Actively working to **
**Optimize photo-z’s**
**Understand photo-z errors **
**Improve mock galaxy and cluster catalogs**
**Optimize filter bandpasses**
**Derive photo-z requirements set by**** ****cosmological parameter analyses**

## Example DES Photo-z Requirements

**Weak lensing tomography:  want *****uncertainty***** in photo-z bias and scatter at the 10****-3**** level**

**Supernovae: robust to DES photo-z error, given existing lower-z SDSS spectro-z supernova sample**

- from D. Huterer

- from Z. Ma

## DES Forecasts: Power of Multiple Techniques

*                                     *

-   Ma, Weller,
-   Huterer, et al.

- Assumptions:
- Clusters:
- 8=0.75, zmax=1.5,
- WL mass calibration
- (no clustering)
- BAO: lmax=300
- WL: lmax=1000
- (no bispectrum; gal-mass
- included in combined)
- Statistical+photo-z
- systematic errors 0.002 only
- Spatial curvature, galaxy bias
- marginalized
- Planck CMB prior

*w*(*z*)* =w**0**+w**a*(1*–a*)           68% CL

- geometric

- geometric+
- growth

- Clusters
- if 8=0.9

## Summary

**DES will measure dark energy using 4 complementary probes (****clusters, weak lensing, BAO, supernovae****), using a ****5000 deg****2**** *****griz***** survey (to 24th mag) with well-calibrated photometry and photo-z’s**
**New ****3 deg****2**** DECam**** mosaic camera provides order of magnitude improvement in survey power over current CTIO Mosaic II camera**
**The DES plans to start observing in late 2009, assuming DOE project approval**
**The DES will serve as a valuable legacy data set for cosmology and astrophysics studies for the community**
**DES is in unique international position to synergize with SPT and VISTA on DETF Stage III time scale;  precursor to more ambitious Stage IV projects like LSST and JDEM**