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Observing Dark Energy

Observing Dark Energy. SDSS, DES, WFMOS teams. Understanding Dark Energy. 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?

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Observing Dark Energy

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  1. Observing Dark Energy SDSS, DES, WFMOS teams

  2. Understanding Dark Energy • 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 (ISW) No compelling theory, must be observational driven

  3. Massive Surveys Need large surveys of the Universe to measure DE accurately SDSS & AS2 ISW SDSS SN Survey (Smith’s talk) Baryon Acoustic Oscillations (BAO) Dark Energy Survey (DES) The power of photo-z’s (Lahav’s talk) WFMOS by Gemini/Subaru The power of spectroscopy

  4. SDSSwww.sdss.org.uk/dr5 SDSSwww.sdss.org DR5: Million spectra, 8000 sq degs Extension (2005-2008): Legacy, SNe, Galaxy

  5. Integrated Sachs-Wolfe Effect Dark Energy effects the rate of growth of structure in Universe • Poisson equation with dark energy: • In a flat, matter-dominated universe (CMB tells us this), then density fluctuations grow as: • Therefore, curvature or DE gives a change in the gravitational potential

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

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

  8. 6300 sq degrees Achromatic 5 detection ISW Detected Update of the Scranton et al. (2003) paper

  9. Giannantonio et al. (2006) Cross-correlation of WMAP3 and SDSS quasars WMAP3 best fit 0.075<m<0.45 -1.15<w<-0.76 Detection of DE at z>1

  10. Evolution of DE Consistent with w=-1 Rules out models D(z=1.5) > 0.5

  11. LCDM DGP Modified Gravity Song et al. (2006)

  12. N S SDSS SN Survey 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) • WHT/NTT leading spectroscopic follow-up (Smith talk)

  13. DES SN Survey SN surveys are now systematics limited Focus on elliptical hosts as less dust and no SNII DES will survey 9deg2 to z=1 detecting ~300 ellipticals Ia’s in 5 years Target clusters (boost of a few) Sullivan et al. (2003)

  14. Baryon Acoustic Oscillations m=0.24 best fit WMAP model 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 WMAP3 Percival et al. 2006 SDSS DR5 520k galaxies

  15. Cosmological Constraints Standard ruler (flat,h=0.73,b=0.17) Percival et al. (2006) h=0.72±0.08 HST m=0.256+0.049-0.029 99.74% detection Best fit m=0.26 Sullivan et al. (2003) m0.275h WMAP3 m=0.256+0.029-0.024 mh2 WMAP3 m=0.256+0.019-0.023

  16. 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 ~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

  17. Parkinson et al. (2007) Emission-line galaxies 5600 deg2 at z=1.1 (dz=0.3) 150 deg2 at z=3.15 (dz=0.2) FoM an order of magnitude larger than SDSS (dw=4%) Optimum is broadly peaked and insensitive to other surveys Now investigating curvature and other w(z) models (Clarkson et al. 2007) WFMOS Surveys Optimize instrument parameters

  18. Measure distance to 1% at z=0.35 and z=0.6 10000 deg2 with 1.5m LRGs to z=0.8 (median z= 0.5) 100k quasars as well Starting 2009 7 times more volume After SDSSII Baryon Oscillation Spectroscopic Survey (BOSS) 2SLAQ

  19. ISW has measured density of DE at z>1; looks like a cosmological constant SDSS SN Survey will deliver >500 Ia’s this year. SN surveys are now systematics dominated (DES will exploit Ia’s in elliptical galaxies) SDSS BAO measures are robust and deliver 10% measurements on cosmological parameters WFMOS and AS2 will move BAO to 1% level Strong degeneracy with curvature; need many distance scale measures as function of redshift Conclusions

  20. 2057 (April 1st 2007)

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