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

August 1st 2006Durham "Cosmic Frontiers" Outline Dark Energy Primer Dark Energy Primer Growth of Structure: ISW Growth of Structure: ISW Geometry: SN & BAO Geometry: SN & BAO

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

August 1st 2006Durham "Cosmic Frontiers" 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 (CL, WL) No compelling theory, so must be observational driven

August 1st 2006Durham "Cosmic Frontiers" DETF Report (Kolb et al) 138 pages condensed to this column SN & BAO - safe, but only 100% improvement CL & WL - risky, but big gains Clear recommendation to do multiple measurement with one being the growth of structure to test GR

August 1st 2006Durham "Cosmic Frontiers" The effect of DE is only seen on large scales, therefore we need to study large volumes to beat “cosmic variance” DE is a small effect (even on large scales) so need large samples to control statistical and systematic errors We need to understand the redshift evolution of DE (w(z)) DE require “big surveys” Challenge to experimentalists to build massive surveys (in size and number) with high precision

August 1st 2006Durham "Cosmic Frontiers" “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

SDSS DR5: Million spectra, 8000 sq degs Extension ( ): Legacy, SNe, Galaxy

August 1st 2006Durham "Cosmic Frontiers" Stage I & II: Growth of Structure

Late-time Integrated Sachs Wolfe (ISW) Effect DE also effects the growth of structure i.e. Poisson equation with dark energy: 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: 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 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

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

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

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

August 1st 2006Durham "Cosmic Frontiers" Theoretical Predictions W-band z=0.49 LRGs  m =0.3  m =0.2 Degeneracy between b, n(z) and cosmology

August 1st 2006Durham "Cosmic Frontiers" Giannantonio et al (astro-ph/ ) WMAP3-photoQSO WMAP3 best fit Detection of DE at z> <  m < <w<-0.76

August 1st 2006Durham "Cosmic Frontiers" 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

August 1st 2006Durham "Cosmic Frontiers" Stage I & II: Geometrical Tests

August 1st 2006Durham "Cosmic Frontiers" bridge low-z (z<0.05; LOSS, SNF) and high-z (0.3<z<1.0; ESSENCE, SNLS) sources 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) understand and minimize systematics of SN Ia as distance indicators (look at correlations with host galaxy properties) SDSSII SNe Survey SDSSII SNe Survey Exploring DE & SNe at an epoch when DE dominates Riess et al. (2004) compilation Astier et al. (2005) 9% measurement of w by 2008 comparable with SNLS 6% measurement of w when combined with SNLS Espana-Bonet, Nichol, Ruiz-Lapuente

August 1st 2006Durham "Cosmic Frontiers" Use the SDSS 2.5m telescope September 1 - November 30 of September 1 - November 30 of Scan 300 square degrees of the sky every 2 days Scan 300 square degrees of the sky every 2 days “Stripe82” (UKIDSS data) “Stripe82” (UKIDSS data) Survey Area NS

August 1st 2006Durham "Cosmic Frontiers"

August 1st 2006Durham "Cosmic Frontiers" 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 Photometric Typing Ia II SN2005hy II

August 1st 2006Durham "Cosmic Frontiers" 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 International Follow-up

August 1st 2006Durham "Cosmic Frontiers" 2005 spectroscopically confirmed + probable SN Ia

August 1st 2006Durham "Cosmic Frontiers" dispersion ~ 0.18 mag internal consistency

August 1st 2006Durham "Cosmic Frontiers" Galaxy-SNe Correlations

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

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?

August 1st 2006Durham "Cosmic Frontiers" BAO 2006 (Percival et al. 2006) WMAP3 SDSS DR5 520k galaxies  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

August 1st 2006Durham "Cosmic Frontiers" Smooth + sinc function (Blake & Glazebrook 2003)

August 1st 2006Durham "Cosmic Frontiers" One parameter Standard ruler (flat,h=0.73,  b =0.17) Percival et al Best fit  m = % detection (3  )

August 1st 2006Durham "Cosmic Frontiers"  m - h Degeneracy h=0.72±0.08 HST  m =  m h WMAP3  m =  m h 2 WMAP3  m =

August 1st 2006Durham "Cosmic Frontiers" 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

August 1st 2006Durham "Cosmic Frontiers" Future Experiments (Stage III)

August 1st 2006Durham "Cosmic Frontiers" 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 1. 1.Cluster counts from optical+SPT 2. 2.Weak lensing maps 3. 3.SNe Ia distance measurement study from 2000 Sne I. I.Unable to gain spectroscopic follow-up for all these Sne. Must use photometric classifications and redshifts II. II.Use SDSSII as a “training sample” to prepare for DES 4. 4.Galaxy angular power spectrum for 300 million galaxies I. I.Baryon Acoustic Oscillations from photo-z’s Each will independently constrain the dark energy eqn of state <10% DES on-sky by 2009

The Dark Energy Survey UK Consortium 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 the UK DES Consortium and are collaborating with the Spanish DES Consortium

August 1st 2006Durham "Cosmic Frontiers" ANNz: Collister & Lahav 2005, Abdalla et al. DES Photo-z’s DES science relies on good photometric estimates of the 300 million expected galaxies Simulated DES Simulated DES+VISTA griz grizJK u-band from VST could remove the low-z errors (ugrizJK)

August 1st 2006Durham "Cosmic Frontiers" 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 + VISTA + VST DES + Planck ISW will be better than LSST for non- constant w models (Pogosian et al. 2005)

August 1st 2006Durham "Cosmic Frontiers" WFMOS 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

August 1st 2006Durham "Cosmic Frontiers" z~1 survey with 2 million galaxies with twice LRG volume 1% accuracy KAOS purple book (Seo, Eisenstein, Blake, Glazebrook) WFMOS will measure w to <4% and dw/dz to <15% Distance Scale

August 1st 2006Durham "Cosmic Frontiers" Testing Modified Gravity DGP LCDM 7  difference Yamamoto et al. 2006

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