Huan Lin 1FNAL ECcmbC Workshop 26 May 2006 The Dark Energy Survey (DES) Huan Lin Experimental Astrophysics Group Fermilab On behalf of the Dark Energy Survey Collaboration

Huan Lin 2FNAL ECcmbC Workshop 26 May 2006 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 ( ) 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) Image credit: Roger Smith/NOAO/AURA/NSF

3 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

Huan Lin 4FNAL ECcmbC Workshop 26 May 2006 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: 10σ griz = 24.6, 24.1, 24.3, 23.9 – Point sources: 5σ 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 SPT overlap area SDSS Southern Equatorial Stripe Tie region

Huan Lin 5FNAL ECcmbC Workshop 26 May 2006 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

Huan Lin 6FNAL ECcmbC Workshop 26 May 2006 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

Huan Lin 7FNAL ECcmbC Workshop 26 May 2006 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

Huan Lin 8FNAL ECcmbC Workshop 26 May 2006 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

Huan Lin 9FNAL ECcmbC Workshop 26 May 2006 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

Huan Lin 10FNAL ECcmbC Workshop 26 May 2006 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

Huan Lin 11FNAL ECcmbC Workshop 26 May 2006 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

Huan Lin 12FNAL ECcmbC Workshop 26 May 2006 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

Huan Lin 13FNAL ECcmbC Workshop 26 May 2006 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.

Huan Lin 14FNAL ECcmbC Workshop 26 May 2006 DES: ISW  8 =1.0  8 =0.9 w/ photo-z w/o photo-z from Gaztanaga, Cabre et al.

15 DES: Type Ia Supernovae Repeat observations of 40 deg 2, 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

Huan Lin 16FNAL ECcmbC Workshop 26 May 2006 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

Huan Lin 17FNAL ECcmbC Workshop 26 May 2006 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 o Optimize photo-z’s o Understand photo-z errors o Improve mock galaxy and cluster catalogs o Optimize filter bandpasses o Derive photo-z requirements set by cosmological parameter analyses

Huan Lin 18FNAL ECcmbC Workshop 26 May 2006 Example DES Photo-z Requirements ● Weak lensing tomography: want uncertainty in photo-z bias and scatter at the 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, z max =1.5, WL mass calibration (no clustering) BAO: l max =300 WL: l max =1000 (no bispectrum; gal-mass included in combined) Statistical+photo-z systematic errors 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

Huan Lin 20FNAL ECcmbC Workshop 26 May 2006 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