“Observing Dark Energy”

““Observing Dark Energy”Observing Dark Energy”

Bob NicholBob Nichol

ICG, PortsmouthICG, 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 2006August 1st 2006 Durham "Cosmic Frontiers"Durham "Cosmic Frontiers"

Outline Dark Energy PrimerDark Energy Primer Growth of Structure: ISWGrowth of Structure: ISW Geometry: SN & BAOGeometry: SN & BAO

(DARK) MATTER

(DA

RK

) EN

ER

GY

CMB

SN

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


Understanding Dark EnergyUnderstanding 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


““Massive Surveys”Massive Surveys”

SDSS: first “massive” survey ISW SDSSII SNe

Baryon Acoustic Oscillations (BAO)

DES: next “massive” imaging surveyThe power of photo-z’s

WFMOS: next “massive” redshift surveyThe power of spectroscopy

SDSSSDSSwww.sdss.orgwww.sdss.org

DR5: Million spectra, 8000 sq degs

Extension (2005-2008): Legacy, SNe, Galaxy

Late-time Integrated Late-time Integrated Sachs Wolfe (ISW) EffectSachs Wolfe (ISW) Effect

DE also effects the growth of structure i.e. Poisson equation DE also effects the growth of structure i.e. Poisson equation with dark energy:with dark energy:

In a flat, matter-dominated universe (CMB tells us this), then In a flat, matter-dominated universe (CMB tells us this), then density fluctuations grow as:density fluctuations grow as:

Therefore, for a flat geometry, changes in the gravitational Therefore, for a flat geometry, changes in the gravitational potential are a direct physical measurement of Dark Energy as potential are a direct physical measurement of Dark Energy as they should be non-evolving if DE=0they should be non-evolving if DE=0

[ ])(4' 12DEma

d

dGk δρδρη

π +−=Φ −

€

δρm ∝ a

Experimental Set-upExperimental Set-up

Nolta et al, Boughn & Crittenden, Myers et al, Ashfordi et al, Fosalba Nolta et al, Boughn & Crittenden, Myers et al, Ashfordi et al, Fosalba et al., Gaztanaga et al., Rassat et al.et al., Gaztanaga et al., Rassat et al.

WMAP-SDSS WMAP-SDSS cross-correlationcross-correlation

WMAP W band

Luminous Red Galaxies (LRGs)

No signal in a flat, matter dominated Universe

ISW DetectedISW Detected 5300 sq degrees 5300 sq degrees Achromatic Achromatic

(no (no contamination)contamination)

Upto 5Upto 5 detection detection

Update of Scranton et al. 2003


Theoretical PredictionsTheoretical PredictionsW-band z=0.49 LRGs

m=0.3

m=0.2

Degeneracy between b, n(z) and cosmology


Giannantonio et al. 2006(astro-ph/0607572)

WMAP3-photoQSO

WMAP3 best fit

Detection of DE at z>1

0.075<0.075<mm<0.45<0.45-1.15<-1.15<ww<-0.76<-0.76


Evolution of DEEvolution of DEw=-1 survives w=-1 survives another (weak) another (weak)

testtest

But rules out models But rules out models with with DD(z=1.5) > (z=1.5) >

0.50.5

Important for tests Important for tests of modified gravity of modified gravity

theories theories


• bridge low-z (z<0.05; bridge low-z (z<0.05; LOSS, SNF) and high-z LOSS, SNF) and high-z (0.3<z<1.0; ESSENCE, (0.3<z<1.0; ESSENCE, SNLS) sourcesSNLS) sources

• understand and understand and minimize systematics of minimize systematics of SN Ia as distance SN Ia as distance indicators (look at indicators (look at correlations with host correlations with host galaxy properties)galaxy properties)

SDSSII SNe SurveySDSSII SNe SurveyExploring 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 SNLSEspana-Bonet, Nichol, Ruiz-Lapuente


Use the SDSS 2.5m telescopeUse the SDSS 2.5m telescope• September 1 - November 30 of 2005-2007September 1 - November 30 of 2005-2007• Scan 300 square degrees of the sky every 2 daysScan 300 square degrees of the sky every 2 days• ““Stripe82” (UKIDSS data)Stripe82” (UKIDSS data)

Survey AreaSurvey Area

N S



• 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 TypingPhotometric Typing

IaIa

II

SN2005hy

II


• 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-upInternational Follow-up


2005

spe

ctro

scop

ical

ly c

onfi

rmed

+ p

roba

ble

SN

Ia


dispersion ~ 0.18 maginternal consistency


Galaxy-SNe CorrelationsGalaxy-SNe Correlations

Baryon OscillationBaryon Oscillation

o Gravity squeezes the gas, pressure pushes back! Gravity squeezes the gas, pressure pushes back! They oscillateThey oscillate

o When the Universe cools below 3000K these When the Universe cools below 3000K these sound waves are frozen in sound waves are frozen in

Courtesy of Wayne Hu

Cosmic Microwave Cosmic Microwave BackgroundBackground

• 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?


BAO 2006BAO 2006(Percival et al. 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


Smooth + sinc function(Blake & Glazebrook 2003)


One One parameteparamete

r r Standard ruler(flat,h=0.73,b=0.17)

Percival et al. 2006

Best fit m=0.2699.74% detection (3)


mm - h Degeneracy - h Degeneracy

h=0.72±0.08 HST

m=0.256+0.049-

0.029

m0.275h WMAP3

m=0.256+0.029-

0.024

mh2 WMAP3

m=0.256+0.019-

0.023


SummarySummary

ISW detected at several redshifts to z~1 and consistent with cosmological constant.

Good news for people looking for DE at high zGood 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


Future ExperimentsFuture Experiments(Stage III)(Stage III)


Dark Energy Survey Dark Energy Survey (DES)(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. Cluster counts from optical+SPT2. Weak lensing maps3. SNe Ia distance measurement study from 2000 Sne

I. Unable to gain spectroscopic follow-up for all these Sne. Must use photometric classifications and redshifts

II. Use SDSSII as a “training sample” to prepare for DES

4. Galaxy angular power spectrum for 300 million galaxies I. Baryon Acoustic Oscillations from photo-z’s

Each will independently constrain the dark energy eqn of state <10%

DES on-sky by 2009DES on-sky by 2009

The Dark Energy Survey The Dark Energy Survey UK Consortium 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


ANNz: Collister & Lahav 2005, Abdalla et al.

DES Photo-z’sDES Photo-z’sDES science relies on good photometric

estimates of the 300 million expected galaxies

Simulated DES

Simulated DES+VISTA

griz

grizJKu-band from VST could remove the

low-z errors(ugrizJK)


• 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 + VSTDES + VISTA + VST

DES + Planck ISW will be better than LSST for

non-constant w models(Pogosian et al. 2005)


WFMOSWFMOS• 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


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 ScaleDistance Scale


Testing Modified Testing Modified GravityGravity

DGPLCDM

7 difference

Yamamoto et al. 2006

Summary IISummary IIa) 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

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“Observing Dark Energy”

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