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“Observing Dark Energy”

“Observing Dark Energy”. Bob Nichol ICG, Portsmouth. SDSS, DES & WFMOS teams. Special thanks to Masao Sako, David Weinberg, Andy Connolly, Albert Stebbins, Rob Crittenden, Daniel Eisenstein, Josh Frieman, Tom Giannantonio, Ryan Scranton, Will Percival. Outline. Dark Energy Primer

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“Observing Dark Energy”

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  1. “Observing Dark Energy” Bob Nichol ICG, Portsmouth SDSS, DES & WFMOS teams Special thanks to Masao Sako, David Weinberg, Andy Connolly, Albert Stebbins, Rob Crittenden, Daniel Eisenstein, Josh Frieman, Tom Giannantonio, Ryan Scranton, Will Percival

  2. Outline • Dark Energy Primer • Growth of Structure: ISW • Geometry: SN & BAO Durham "Cosmic Frontiers"

  3. SNe and CMB force us into a Universe ~75% DE and ~25% DM. We are trace elements! Can this be true? SN CMB (DARK) ENERGY (DARK) MATTER

  4. Understanding Dark Energy No compelling theory, so must be observational driven We can make progress on questions: • Is DE just a cosmological constant (w(z)=-1)? (Make better observations and push to higher z) • Is DE a new form of matter (with negative effective pressure) or a breakdown of GR? (Study DE using different probes) But there are only two broad avenues: • Geometrical tests (SN, BAO) • Growth of structure (CL, WL) Durham "Cosmic Frontiers"

  5. “Massive Surveys” SDSS: first “massive” survey ISW SDSSII SNe Baryon Acoustic Oscillations (BAO) DES: next “massive” imaging survey The power of photo-z’s WFMOS: next “massive” redshift survey The power of spectroscopy Durham "Cosmic Frontiers"

  6. SDSSwww.sdss.org DR5: Million spectra, 8000 sq degs Extension (2005-2008): Legacy, SNe, Galaxy

  7. Late-time Integrated Sachs Wolfe (ISW) Effect • DE also effects the growth of structure i.e. Poisson equation with dark energy: • In a flat, matter-dominated universe (CMB tells us this), then density fluctuations grow as: • Therefore, for a flat geometry, changes in the gravitational potential are a direct physical measurement of Dark Energy as they should be non-evolving if DE=0

  8. Experimental Set-up Nolta et al, Boughn & Crittenden, Myers et al, Ashfordi et al, Fosalba et al., Gaztanaga et al., Rassat et al.

  9. WMAP-SDSS cross-correlation WMAP W band Luminous Red Galaxies (LRGs) No signal in a flat, matter dominated Universe

  10. 5300 sq degrees Achromatic (no contamination) Upto 5 detection ISW Detected Update of Scranton et al. 2003

  11. Theoretical Predictions W-band z=0.49 LRGs m=0.2 m=0.3 Degeneracy between b, n(z) and cosmology Durham "Cosmic Frontiers"

  12. Giannantonio et al. 2006 (astro-ph/0607572) WMAP3 best fit WMAP3-photoQSO 0.075<m<0.45 -1.15<w<-0.76 Detection of DE at z>1 Durham "Cosmic Frontiers"

  13. Evolution of DE w=-1 survives another (weak) test But rules out models with D(z=1.5) > 0.5 Important for tests of modified gravity theories Durham "Cosmic Frontiers"

  14. SDSSII SNe SurveyExploring DE & SNe at an epoch when DE dominates • bridge low-z (z<0.05; LOSS, SNF) and high-z (0.3<z<1.0; ESSENCE, SNLS) sources • understand and minimize systematics of SN Ia as distance indicators (look at correlations with host galaxy properties) Riess et al. (2004) compilation 9% measurement of w by 2008 comparable with SNLS 6% measurement of w when combined with SNLS Durham "Cosmic Frontiers" Astier et al. (2005) Espana-Bonet, Nichol, Ruiz-Lapuente

  15. Survey Area N S Use the SDSS 2.5m telescope • September 1 - November 30 of 2005-2007 • Scan 300 square degrees of the sky every 2 days • “Stripe82” (UKIDSS data) Durham "Cosmic Frontiers"

  16. Durham "Cosmic Frontiers"

  17. Photometric Typing • Color-type SNe candidates using nightly g r i data • fit light-curve for redshift, extinction, stretch for Ia • Able to type with >90% efficiency after ~2 - 4 epochs SN2005hy Ia II Ia II Durham "Cosmic Frontiers"

  18. International Follow-up • 332 spectroscopically confirmed SN Ia • 254 unconfirmed Ia’s with good LC’s (galaxy redshifts exist for 60) • Many Ia’s now have multi-epoch spectra • Follow-up on NTT, WHT, Subaru, ARC3.5m, HET, MDM • One more season, expecting over 500 SNe Durham "Cosmic Frontiers"

  19. 2005 spectroscopically confirmed + probable SN Ia Durham "Cosmic Frontiers"

  20. dispersion ~ 0.18 mag internal consistency Preliminary Durham "Cosmic Frontiers"

  21. Galaxy-SNe Correlations Durham "Cosmic Frontiers"

  22. Baryon Oscillation • Gravity squeezes the gas, pressure pushes back! They oscillate • When the Universe cools below 3000K these sound waves are frozen in Courtesy of Wayne Hu

  23. Cosmic Microwave Background • Effect of this sound wave already discovered in relic light of the early universe i.e. the CMB! • That was the Universe at 400,000 years. Can we see these sound waves today?

  24. BAO 2006(Percival et al. 2006) m=0.24 best fit WMAP model WMAP3 Miller et al. 2001, Percival et al. 2001, Tegmark et al. 2001, Cole et al. 2005, Eisenstein et al. 2005, Hutsei 2006, Blake et al. 2006, Padmanabhan et al. 2006 SDSS DR5 520k galaxies Durham "Cosmic Frontiers"

  25. Smooth + sinc function (Blake & Glazebrook 2003) Durham "Cosmic Frontiers"

  26. One parameter Standard ruler (flat,h=0.73,b=0.17) Best fit m=0.26 99.74% detection (3) Percival et al. 2006 Durham "Cosmic Frontiers"

  27. m - h Degeneracy h=0.72±0.08 HST m=0.256+0.049-0.029 mh2 WMAP3 m=0.256+0.019-0.023 m0.275h WMAP3 m=0.256+0.029-0.024 Durham "Cosmic Frontiers"

  28. Summary • ISW detected at several redshifts to z~1 and consistent with cosmological constant. Good news for people looking for DE at high z • 229 SDSS SNIa’s so far, 400 by 2007 Systematics limited and will deliver w to 6% • BAO have been detected at 3m=0.256 to 10% from acoustic scale Good news for future BAO experiments Durham "Cosmic Frontiers"

  29. Future Experiments(Stage III) Durham "Cosmic Frontiers"

  30. Dark Energy Survey (DES) • 5000 sq deg multiband (g,r,i,z) survey of SGP using CTIO Blanco with a new wide-field camera • 40 sq deg time domain search for SNe • Cluster counts from optical+SPT • Weak lensing maps • SNe Ia distance measurement study from 2000 Sne • Unable to gain spectroscopic follow-up for all these Sne. Must use photometric classifications and redshifts • Use SDSSII as a “training sample” to prepare for DES • Galaxy angular power spectrum for 300 million galaxies • Baryon Acoustic Oscillations from photo-z’s Each will independently constrain the dark energy eqn of state <10% DES on-sky by 2009 Durham "Cosmic Frontiers"

  31. 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 in February 2005 requesting £ 1.5 M for the DES optical design. In March 2006, PPARC Council announced that it“will seek participation in DES”. (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 theUK DES Consortium and are collaborating with the Spanish DES Consortium

  32. u-band from VST could remove the low-z errors (ugrizJK) DES Photo-z’s Simulated DES DES science relies on good photometric estimates of the 300 million expected galaxies griz grizJK Simulated DES+VISTA ANNz: Collister & Lahav 2005, Abdalla et al. Durham "Cosmic Frontiers"

  33. DES + VISTA + VST • Give photo-z’s to z~2 with  < 0.1 • BAO improves by 50% with VISTA; 15% error on w just the BAO scale • Targets for Gemini, VLT • Overlap with CLOVER, SPT DES + Planck ISW will be better than LSST for non-constant w models (Pogosian et al. 2005) Durham "Cosmic Frontiers"

  34. Proposed MOS on Subaru via an international collaboration of Gemini and Japanese astronomers 1.5deg FOV with 4500 fibres feeding 10 low-res spectrographs and 1 high-res spectrograph First-light in 2013 ~20000 spectra a night (2dfGRS at z~1 in 10 nights) DE science, Galactic archeology, galaxy formation studies and lots of ancillary science from database WFMOS Durham "Cosmic Frontiers"

  35. Distance Scale KAOS purple book (Seo, Eisenstein, Blake, Glazebrook) z~1 survey with 2 million galaxies with twice LRG volume 1% accuracy WFMOS will measure w to <4% and dw/dz to <15% Durham "Cosmic Frontiers"

  36. Testing Modified Gravity DGP LCDM 7 difference Yamamoto et al. 2006 Durham "Cosmic Frontiers"

  37. Summary II • Experiments by 2010 will measure w (constant) to a few %, but that doesn’t mean we understand it! • Next generation surveys will probe w(z) and start testing “growth of structure” measurements of DE

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