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Probes of Dark Energy

Probes of Dark Energy. Cluster/Halo abundances volume, structure growth Galaxy Clustering standard rulers, structure Type Ia Supernovae standard candles Weak Lensing geometry, structure Complementarity: of systematic errors and of cosmological

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Probes of Dark Energy

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  1. Probes of Dark Energy Cluster/Halo abundances volume, structure growth Galaxy Clustering standard rulers, structure Type Ia Supernovaestandard candles Weak Lensinggeometry, structure Complementarity:of systematic errors and of cosmological parameter degeneracies Our collaboration has substantial, practical experience in all 4 key project areas

  2. Refregier

  3. DES Weak Lensing Marginalized 68% CL DES constraints • Measure shapes for ~300 million source galaxies with z = 0.7 • Shear-shear & galaxy-shear correlations probe distances & growth rate of perturbations • Mass Power spectrum determined by CMB (WMAP) Sky area, depth, photo-z’s, image quality & stability

  4. Evolution of Dark Energy • Planck CMB priors • Cosmic shear to l=3000 • Galaxy-shear to l=1000 • Lens galaxies in halos above 1012.5 Msun in bins of z=0.1 to z=1 • Source galaxies in bins of z=0.28 to z=1.1 plus 1 high-z bin

  5. Weak Lensing Systematics • Residual PSF anisotropy (telescope, atmosphere) • Optical design --> PSF map • Pixel size requirement • Systematic Photo-z errors (under study) Refregier

  6. Cluster Weak Lensing Mass Map (BTC on Blanco) Optical survey independently calibrates SZ cluster mass estimates through WL and richness

  7. Type Ia SNe as calibrated `Standard’ Candles Peak brightness correlates with decline rate (Phillips) After correction, dispersion in peak brightness ~ 0.12-0.15 mag Luminosity Time

  8. Type Ia Supernovae Advantages: • small dispersion in peak brightness (std. candles) • single objects (simpler than galaxies) • can be observed over wide redshift range(bright) • Challenges/Systematic concerns: • dust extinction in host galaxy • chemical composition variations/evolution • evolution of progenitor population • photometric calibration • Malmquist bias • environmental differences • K correction uncertainties

  9. DES Supernovae • Repeat observations of 40 deg2 , 10% of survey time • ~1900 well-measured riz SN Ia lightcurves, 0.25 < z < 0.75 • Larger sample, improved z-band response compared to ESSENCE, CFHTLS • Combination of spectroscopic (~25%) and photometric redshifts • Develop color typing and SN photo-z’s (critical for LSST) DES constraints (assuming  = 0.2 mag)

  10. The Dark Energy Survey in Context • Connecting Quarks with the Cosmos, Beyond Einstein, Quantum Universe, Physics of the Universe, HEPAP, DOE OS Facility Plan, … • All identified Dark Energy as one of the most profound questions in fundamental physics, ripe for experimental progress • Endorsed a multi-pronged approach to dark energy from ground- and space-based telescopes • To make progress in understanding Dark Energy, we must reach greater precision: determineDE, w = p/, and its evolution

  11. The Dark Energy Survey in Context: Toward A U.S. Dark Energy Program • Coherent program aimed at increasing Dark Energy precision over the next ~15 years desirable • Sequence of logical, incremental steps of increasing scale, technical complexity, and scientific reach • Increase precision in w from ~20% today* to ~ few % (robustly) over this period. Determine evolution dw/dz to ~20% (current constraints very weak). • DES as logical next step in Dark Energy measurements beyond current surveys *Note: all quoted (1) errors on w assume it does not evolve (and beware priors)

  12. Dark Energy: where we are now (w) ~ 0.15*, w < –0.76 (95%) 95% constraints assuming w = –1 assuming w constant Tegmark, etal Key priors: scale-free spectrum, no gravity waves, massless neutrinos, simple bias Additional prior: flat Universe *from CMB+LSS+SNe; no single dataset constrains w better than ~30%

  13. Riess, etal

  14. Dark Energy: 2004-2008 (w) ~ 0.1* • Supernovae: ESSENCE, CFHTLS, HST, SNF, SDSS,… many 100’s of SNe Ia over z ~ 0.1-0.8 • Weak Lensing: Deep Lens, CFHTLS, RCS II, … ~200-1000 sq. deg. deep multi-band imaging • Cluster SZ: APEX, ACT, SPT,… ~200 --> 4000 sq. deg. *SNE+WMAP combined

  15. The Dark Energy Survey in Context: 2009-2013 Logical next step in dark energy measurements: • Will measure w to ~ 0.05–0.15 statistical accuracy* using multiple complementary probes, and begin to constrain dw/dz • Scientific and technical precursor to the more ambitious Dark Energy projects to follow: LSST and SNAP • DES in unique position to synergize with SPT on this timescale • Cannot be done with any existing facility: Blanco+DECAM ~5 times faster survey instrument than CFHT+Megacam, >10x faster than any current U.S. facility, ~2x faster than PanSTARRS I • Complementarity: DUO (X-ray Clusters), KAOS *accuracy on each probe separately, with at most weak priors

  16. Dark Energy: 2012/3 and Beyond • • Ground: LSSTDedicated 8m telescope with wide FOV imager • Space: JDEM2m optical/NIR wide-field telescope in space • Goals:wto few %,dw/dzto ~20% • Designed as `ultimate’ Dark Energy experiments, they must have exquisite control of systematic errors to reach the next level of cosmological precision • Timescales and costs reflect this

  17. A National Wide-Field Imaging Facility • Blanco+DECAM will be a unique resource for the astronomy community.

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