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Surveys of Dark Energy: Challenges and Prospects

Surveys of Dark Energy: Challenges and Prospects. Ofer Lahav University College London. Cosmology post WMAP/2dF/SDSS/… The Dark Energy Survey Photometric redshifts, and cross-talk with cosmic probes The future of the local universe. “Evidence” for Dark Energy. SN Ia CMB

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Surveys of Dark Energy: Challenges and Prospects

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  1. Surveys of Dark Energy:Challenges and Prospects Ofer Lahav University College London • Cosmology post WMAP/2dF/SDSS/… • The Dark Energy Survey • Photometric redshifts, and cross-talk with cosmic probes • The future of the local universe

  2. “Evidence” for Dark Energy • SN Ia • CMB • LSS – Baryonic Oscillations • Cluster counts • Weak Lensing • Integrated Sachs Wolfe Physical effects: * Geometry * Growth of Structure

  3. The Chequered History of theCosmological Constant  The old CC problem: Theory exceeds observational limits on  by 10120 ! The new CC problem: Why are the amounts of Dark Matter and Dark Energy so similar?

  4. Globalisation and the New Cosmology • How is the New Cosmology affected by Globalisation? • Recall the Cold War era: Hot Dark Matter/top-down (East) vs. Cold Dark Matter/bottom-up (West) • Is the agreement on the `concordance model’ a product of Globalisation? OL, astro-ph/0610713

  5. Matter and Dark Energy tell space how to curve: k = 1 -m -  Curvature Matter Dark Energy(Vacuum)

  6. Matter and Dark Energy tell space how to curve: k = 1 -m -  Curvature Matter Dark Energy(Vacuum) OR modified curvature k +  = 1 -m

  7. The Universe is accelerating at present if q0 = m/2 -  < 0 e.g. For m = 0.3 and  = 0.7 : k = 0 (the Universe is flat) and the Universeis accelerating (but only ‘recently’, z<0.7)

  8. Spherical Collapse d2r/dt2 = -GM/r2 + (/3) r cf. Newton-Hooke force cf. Inflation For the mass of the Local Group (MW+M31) the forces are equal at r= 1.3 Mpc Dark Energy also affects the virialization radius the collapsed object (OL et al. 91; Maor & OL 05)

  9. Probing Dark Matter & Dark Energy • Through the history of the expansion rate: H2(z) = H20 [M (1+z) 3 + DE (1+z) 3 (1+w) ] (flat Universe) matter dark energy (constant w) P = w  • Comoving distance r(z) =  dz/H(z) • Standard Candles dL(z) = (1+z) r(z) • Standard Rulers dA(z) = (1+z)1 r(z) • The rate of growth of structure also determined by H(z) and by any modifications of gravity on large scales

  10. Baryon Wiggles as Standard Rulers

  11. DUNE: Dark UNiverse Explorer • Mission baseline: • 1.2m telescope • FOV 0.5 deg2 • PSF FWHM 0.23’’ • Pixels 0.11’’ • GEO (or HEO) orbit • Surveys (3-year initial programme): • WL survey: 20,000 deg2 in 1 red broad band, 35 galaxies/amin2 with median z ~ 1, ground based complement for photo-z’s • Near-IR survey (J,H). Deeper than possible from ground. Secures z > 1 photo-z’s • SNe survey: 2£60 deg2, observed for 9 months each every 4 days in 6 bands, 10000 SNe out to z ~ 1.5, ground based spectroscopy

  12. Survey Filters Depth Dates Status Sq. Degrees CTIO 75 1 shallow published VIRMOS 9 1 moderate published COSMOS 2 (space) 1 moderate complete 36 4 deep complete DLS (NOAO) Subaru 30? 1? deep observing 2005? 170 5 moderate observing CFH Legacy 2004-2008 830 3 shallow approved RCS2 (CFH) 2005-2007 VST/KIDS/ VISTA/VIKING 1700 4+5 moderate 2007-2010? 50%approved 5000 4 moderate proposed DES (NOAO) 2008-2012? Pan-STARRS ~10,000? 5? moderate ~funded 2006-2012? LSST 15,000? 5? deep proposed 2014-2024? 1000+ (space) 9 deep proposed JDEM/SNAP 2013-2018? Imaging Surveys proposed moderate 5000? 4+5 2010-2015? VST/VISTA proposed moderate 2+1? DUNE 20000? (space) 2012-2018? Y. Mellier

  13. US Dark Energy Task Force Recommendations • An immediate start of a near-term program (which we call Stage III) designed to advance our knowledge of dark energy and prepare for the ultimate “Stage IV” program,which consists of a combination of large survey telescopes and/or a space mission. • cf. PPARC and ESO/ESA reports Advocate ‘a Figure of Merit’

  14. DETF FoM / 1/[ellipse area]

  15. The Dark Energy Survey Blanco 4-meter at CTIO • Study Dark Energy using 4 complementary techniques: I. Cluster Counts II. Weak Lensing III. Baryon Acoustic Oscillations IV. Supernovae • Two multi-band surveys 5000 deg2g, r, i, z 40 deg2 repeat (SNe) • Build new 3 deg2 camera and data management system Survey 2010-2015 (525 nights) Response to NOAO AO 300,000,000 photometric redshifts

  16. 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, R. Maartnes, W. Percival University of Sussex: A. Liddle, K. Romer plus postdocs and students

  17. The Dark Energy Survey UK Consortium (I) PPARC funding: O. Lahav (PI), P. Doel, M. Barlow, S. Bridle, S. Viti, J. Weller (UCL), R. Nichol (Portsmouth), G. Efstathiou, R. McMahon, W. Sutherland (Cambridge) J. Peacock (Edinburgh) Submitted a proposal to PPARC requesting £ 1.7M for the DES optical design. In March 2006, PPARC Council announced that it “will seek participation in DES”. PPARC already approved £220K for current R&D. (II) SRIF3 funding: R. Nichol, R. Crittenden, R. Maartens, W. Percival (ICG Portsmouth) K. Romer, A. Liddle (Sussex) Funding the optical glass blanks for the UCL DES optical work These scientists will work together through the UK DES Consortium. Other DES proposals are under consideration by US and Spanish funding agencies.

  18. The Dark Energy Survey Camera: DECam DECam will replace the prime focus cage 4m Blanco telescope

  19. Supernovae Ia • 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

  20. Background sources Dark matter halos Observer • Statistical measure of shear pattern, ~1% distortion • Radial distances depend on geometry of Universe • Foreground mass distribution depends on growth of structure A. Taylor

  21. Assumptions: Clusters: SPT-selected, 8=0.75, zmax=1.5, WL mass calibration (no clustering self-calibration) Mass-observable power-law w/ Lognormal spread BAO:lmax=300 WL:lmax=1000 (no bispectrum or galaxy-shear) Statistical+photo-z systematic errors only Spatial curvature, galaxy bias marginalized Planck CMB prior w(z) =w0+wa(1–a) 68% CL DES Forecasts: Power of Multiple Techniques Ma, Weller, Huterer, etal

  22. DES – Figure of Merit

  23. Photo-z – WL – BAO - SNIa cross talk • Approximately, for a photo-z slice: (w/ w) = a (z/ z) = a (z/z) Ns-1/2 => the target accuracy in w and photo-z scatter z dictate the number of required spectroscopic redshifts Ns =105-106

  24. Photometric redshifts z=0.1 z=3.7 Probe strong spectral features (e.g. 4000 break)

  25. ANNz - Artificial Neural Network z = f(m,w) Output: redshift Input: magnitudes Collister & Lahav 2004 http://www.star.ucl.ac.uk/~lahav/annz.html

  26. *Training on ~13,000 2SLAQ*Generating with ANNz Photo-z for ~1,000,000 LRGsMegaZ-LRG z = 0.046 Collister, Lahav, Blake et al., astro-ph/0607630

  27. Excess Power on Gpc Scale? Blake et al. 06 Padmanabhan et al. 06

  28. DES and VDES DES (griz) DES+VISTA(JK) VISTA J (<21) and K (<19) would improve photo-z by a factor of 2 for z>1 F. Abdalla, M. Banerji, OL, H. Lin, et al.

  29. DES and a Dark Energy Programme • * 4-5 complementary probes • * Survey strategy delivers substantial DE science after 2 years • * Relatively modest (~ $20-30M), low-risk, near-term project with high discovery potential • *Synergy with SPT and VISTA on the DETF Stage III timescale • * Scientific and technical precursor to the more ambitious Stage IV Dark Energy projects to follow: LSST and JDEM

  30. The Future of the Local Universem =0.3 LCDM a = 1 (t= 13.5 Gyr) LCDM a = 6 (t= 42.4 Gyr) OCDM a = 1 (t= 11.3 Gyr) OCDM a = 6 (t= 89.2 Gyr) Hoffman, Dover, Yepes, OL

  31. Some Outstanding Questions: * Vacuum energy (cosmological constant, w= -1.000 after all?) * Dynamical scalar field? * Modified gravity? * Why /m = 3 ? * Non-zero Neutrino mass < 1eV ? * The exact value of the spectral index: n < 1 ? * Excess power on large scales? * Is the curvature zero exactly ?

  32. Extra Slides

  33. Expected performance of DECAM, Blanco, and CTIO site

  34. DeCamOptical Lay Out C1 C2 C3 C4 C5 978mm Filter 1870mm

  35. Sources of uncertainties • Cosmological (parameters and priors) • Astrophysical (e.g. cluster M-T, biasing) • Instrumental (e.g. “seeing”)

  36. MegaZ-LRG Angular power spectra Blake, Collister, Bridle & Lahav, astro-ph/0605303

  37. Blanco Telescope • 4m diameter equatorial mount telescope. • Located at altitude of 2200m at Cerro Tololo Inter-American Observatory (CTIO) , Chile (Lat. 30o 10’ S, Long. 70 o 49’ W).

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