“the present and next generation of large galaxy surveys”

““The present and next The present and next generation of large galaxy generation of large galaxy

surveys”surveys”

Bob NicholBob Nichol

ICG, PortsmouthICG, Portsmouth

Thanks to all my collaborators on SDSS, DES, WFMOS teams

OutlineOutline

• A brief overview of Dark EnergyA brief overview of Dark Energy• Do we believe it? (ISW)Do we believe it? (ISW)• How do we measure it better?How do we measure it better?

SDSS SNeSDSS SNe Baryon acoustic oscillations (BAO)Baryon acoustic oscillations (BAO)

• Future experimentsFuture experiments

June 30th 2006June 30th 2006 Marseille 2006Marseille 2006 33

Brief Review of Brief Review of Evidence for Dark Evidence for Dark

EnergyEnergy(circa 2003)(circa 2003)

Largest oscillations Largest oscillations that are causally that are causally

connectedconnected

Largest oscillations Largest oscillations that are causally that are causally

connectedconnected

(DARK) MATTER

(DA

RK

) EN

ER

GY

CMB

SN

SNe and CMB force us into a Universe ~75% DE and ~25% DM. But is it true But is it true and what is and what is DE?DE?

Parameterize our ignorance using equation of state

W(z) = p


Understanding Dark EnergyUnderstanding Dark Energy(The billion dollar question)

To confirm DE we need to observe it in as many ways as possible, but there are only two broad avenues:• Geometrical tests (distances, volumes)• Growth of structure (cluster counts)

To determine what DE is, we can make progress on two simple 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)No compelling theory, so must be observational driven


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))

We need to measure DE using different methods to understand physics of DE and break degeneracies

DE require “big surveys”DE require “big surveys”

Challenge to experimentalists to build massive surveys (in size and

number) with high precision


““Massive Surveys”Massive Surveys”

SDSS: first “massive” survey SDSSII SNe

Baryon Acoustic Oscillations (BAO)ISW

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

WFMOS: next “massive” redshift surveyThe power of spectroscopy


First, do we believe it?First, do we believe it?

Integrated Sachs Wolfe Integrated Sachs Wolfe (ISW)(ISW)

In a flat matter-dominated universe, the gravitational potential of large-scale fluctuations remain constant

with time

Physical detection of Dark Energy: Effecting the growth of structure

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

LRG selectionLRG selection 5300 sq degrees 5300 sq degrees Achromatic (no Achromatic (no

contamination)contamination) 55 overall overall

Look for ISW at high redshift using SDSS

QSOs

Detection of DE at z=1.5

Rule out Phantom models

Giannantonio et al. 2006


How do we measure it How do we measure it Better?Better?

SDSSSDSS(z~0 universe)

DR4: 849k spectra, 6670 sq degs

Done 07/2005: ~700,000 redshifts, 8000 sq degs

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


• Type Ia supernovae (SNe)Type Ia supernovae (SNe)• spectroscopically confirm spectroscopically confirm

and obtain “well-measured” and obtain “well-measured” light curves of ~500 SN Ia light curves of ~500 SN Ia from z = 0.05 to ~ 0.4from z = 0.05 to ~ 0.4

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

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

• Measure low redshift SNe Measure low redshift SNe raterate

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 SNLS


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

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


• 130 spectroscopically confirmed SN Ia

• 10 spectroscopically probable SN Ia

• 6 SN Ib/c (3 hypernovae)

• 10 SN II (4 type IIn)• 5 AGN• 150 unconfirmed SNe

Ia’s with good light curves (galaxy redshifts for 25 exist)

Results from 2005Results from 2005

<z> = 0.21

Europe leading the way in 2006 with 17

nights on NTT


2005

spe

ctro

scop

ical

ly c

onfi

rmed

+ p

roba

ble

SN

Ia


BAO CosmologyBAO Cosmology

z~0.35

z~1000

Excess of galaxies separated by 500 million light years

LRG

Eisenstien et al. 2005


FLAT GEOMETRYCREDIT: WMAP & SDSS websites

CM

B

Looking back in time in the Universe

FLAT GEOMETRY

SD

SS

GA

LAX

IES




SD

SS

GA

LAX

IES

CM

B


OPEN GEOMETRY




CM

B


CLOSED GEOMETRY

SD

SS

GA

LAX

IES


UNIVERSE IS FLAT TO 1% UNIVERSE IS FLAT TO 1% PRECISIONPRECISION

(Eisenstein et al. 2005)(Eisenstein et al. 2005)

Still the best measurement even after

WMAP3


Summary ISummary I

a) ISW detected at several redshifts to z=1.5 and consistent with cosmological constant

b) ~150 SDSS SNIa’s so far, 500 by 2007. Systematics limited and will deliver w to 6%

c) BAO have been detected to 99.X% and deliver consistent wiggles to WMAP3 for m=0.2XX


Future ExperimentsFuture Experiments


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


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 SNAP 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 2012• ~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


Growth of StructureGrowth of Structure

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” DE measurements of DE

c) BAO have been detected to

“the present and next generation of large galaxy surveys”

Documents

galaxy marseille

large scales

massive surveyssdss

dark energycirca

dark energythe

large samples

large volumes

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