Dark Side of the UniverseDark Side of the Universe

Yun Wang Yun Wang

STScI, January 21, 2008STScI, January 21, 2008

Yun Wang, 1/21/2008

beware of the dark side …

Master Yoda

Yun Wang, 1/21/2008

OutlineOutline

• Dark energy: introduction and current constraints

• Observational methods for dark energy search

• Future prospects

Yun Wang, 1/21/2008

How do we know there is How do we know there is dark energy?dark energy?

We infer its existence via its We infer its existence via its influence on the expansion influence on the expansion

history of the universe.history of the universe.

Yun Wang, 1/21/2008

First Evidence for Dark First Evidence for Dark Energy Energy in the Hubble Diagrams of in the Hubble Diagrams of

SupernovaeSupernovae [ [ddLL((zz)] )] (Riess et al. 1998, Schmidt et al. 1998, (Riess et al. 1998, Schmidt et al. 1998,

Perlmutter et al. 1999)Perlmutter et al. 1999)

Yun Wang, 1/21/2008

Alternative Analysis of First EvidenceAlternative Analysis of First Evidence

Flux-averaged and combined data of 92 SNe Ia from Riess/Schmidt et al. (1998) and Perlmutter et al. (1999). [Wang (2000)]

Deceleration parameter

q0 =m/2-

Data favor q0 <0: cosmic

acceleration

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Wang & Tegmark 2005

w(z) = w0+wa(1-a)

1+z = 1/a

z: cosmological redshift

a: cosmic scale factor

WMAP3

+182 SNe Ia (Riess et al. 2007, inc SNLS and nearby SNe)

+SDSS BAO

(Wang & Mukherjee 2007)

Yun Wang, 1/21/2008

Model-Model-independent independent constraints constraints

on dark on dark energyenergy(as proposed by (as proposed by

Wang & Garnavich 2001)Wang & Garnavich 2001)

Wang & Mukherjee (2007)

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Wang & Mukherjee (2007)[See Wang & Tegmark (2005) for the method to derive uncorrelated estimate of H(z) using SNe.]

H(z) = [da/dt]/a

Yun Wang, 1/21/2008

What is dark energy?What is dark energy?

Two Possibilities:

(1) Unknown energy component(1) Unknown energy component

(2) Modification of Einstein’s theory of general (2) Modification of Einstein’s theory of general relativity (a.k.a. Modified Gravity)relativity (a.k.a. Modified Gravity)

Yun Wang, 1/21/2008

Some Candidates for Dark Some Candidates for Dark EnergyEnergy

cosmological constant (Einstein 1917)

quintessence (Freese, Adams, Frieman, Mottola 1987; Linde 1987; Peebles & Ratra 1988; Frieman et al. 1995; Caldwell, Dave, & Steinhardt 1998; Dodelson, Kaplinghat, & Stewart 2000)

k-essence: (Armendariz-Picon, Mukhanov, & Steinhardt 2000)

Modified Gravity Vacuum Metamorphosis (Parker & Raval 1999) Modified Friedmann Equation (Freese & Lewis 2002)

Phantom DE from Quantum Effects (Onemli & Woodard 2004)

Backreaction of Cosmo. Perturbations (Kolb, Matarrese, & Riotto 2005)

Yun Wang, 1/21/2008

How We Probe Dark EnergyHow We Probe Dark Energy

• Cosmic expansion history HCosmic expansion history H((zz) or DE density ) or DE density XX((zz):):

tells us whether DE is a cosmological constanttells us whether DE is a cosmological constant

H2(z) = 8 G[m(z) + r(z) +X(z)]/3 k(1+z)2

• Cosmic large scale structure growth rate function fCosmic large scale structure growth rate function fgg((zz), ), or or

growth history Ggrowth history G((zz):):

tells us whether general relativity is modifiedtells us whether general relativity is modified

fg(z)=dln/dlna, G(z)=(z)/(0)

=[m-m]/m

Yun Wang, 1/21/2008

Observational Methods for Observational Methods for Dark Energy SearchDark Energy Search

• SNe Ia (Standard Candles):SNe Ia (Standard Candles): method through which DE has been discovered; independent of clustering of matter, probes H(z)

• Baryon Acoustic Oscillations (Standard Ruler): Baryon Acoustic Oscillations (Standard Ruler): calibrated by CMB, probes H(z). [The same observations, if optimized, probe growth rate fg(z) as well.]

• Weak Lensing Tomography and Cross-Weak Lensing Tomography and Cross-Correlation Cosmography: Correlation Cosmography: probes growth factor G(z), and H(z)

• Galaxy Cluster StatisticsGalaxy Cluster Statistics: : probes H(z)

Yun Wang, 1/21/2008

Supernovae as Standard CandlesSupernovae as Standard Candles

Lightcurves of 22 SNe Ia (left, Riess et al. 1999): very different from that of SNe II (below).

Measuring the apparent peak Measuring the apparent peak brightness and the redshift of SNe Ia brightness and the redshift of SNe Ia

gives gives ddLL((zz), hence ), hence HH((zz))

Yun Wang, 1/21/2008

Spectral Signature of SNe IaSpectral Signature of SNe IaPrimary feature: Si II 6355 at

rest=6150ÅSecondary feature: Si II 4130 dip

blueshfted to 4000Å

SN Ia 1999ff (z=0.455):a: Ca II H and K absorptionb: Si II 4130 dip blueshfted to 4000Åc: blueward shoulder of Fe II 4555d: Fe II 4555 and/or Mg II 4481e: Si III 4560 i: Si II 5051

SN IIb 1993J: double peak centered justblueward of 4000Å, due to Ca II H and Kabsorption at 3980Å due to blueshuftedH, but not similar to Ia redward of4100Å. [Coil et al. 2000, ApJ, 544, L111]

Yun Wang, 1/21/2008

Theoretical understanding of SNe Theoretical understanding of SNe IaIa

Binary C/O white dwarf at the Chandrasekher limit (~ 1.4 MSun)

explosion

radioactive decay of 56Ni and 56Co: observed brightness

• explosion: carbon burning begins as a turbulent deflagration, then makes a transition to a supersonic detonation

• earlier transition:

cooler explosion less 56Ni produced: dimmer SN Ia

lower opacity faster decline of the SN brightness

Wheeler 2002 (resource letter)

Yun Wang, 1/21/2008

Calibration of SNe IaCalibration of SNe Ia Phillips 1993 Riess, Press, & Kirshner 1995

Brighter SNe IaBrighter SNe Iadecline more slowlydecline more slowly make a correction make a correction to the brightness based to the brightness based on the decline rate.on the decline rate.

26 SNe Ia with Bmax-Vmax 0.20 fromthe Calan/Tololo sample[Hamuy et al. 1996, AJ, 112, 2398]

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Getting the most distant SNe Getting the most distant SNe Ia:Ia: critical for measuring the evolution in dark energy density:

Wang & Lovelave (2001)

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Ultra Deep Supernova SurveyUltra Deep Supernova Survey

To determine whether SNe Ia are good cosmological standard candles, we need to nail the systematicuncertainties (luminosity evolutionluminosity evolution, gravitational gravitational lensinglensing, dustdust). This will require at least hundreds of SNe Ia at z>1z>1. This can be easily accomplished by doing an ultra deep supernova survey using a dedicated dedicated telescopetelescope, which can be used for other thingssimultaneously (weak lensing, gamma ray burstafterglows, etc).

Wang 2000a, ApJ (astro-ph/9806185)

Yun Wang, 1/21/2008

SNe Ia as Cosmological Standard SNe Ia as Cosmological Standard CandlesCandles

Systematic effects:

dust: can be constrained using multi-color data. (Riess et al. 1998; Perlmutter et al. 1999)

gray dust: constrained by the cosmic far infrared background. (Aguirre & Haiman 2000)

gravitational lensing: its effects can be reduced by flux-averaging. (Wang 2000; Wang, Holz, & Munshi 2002)

SN Ia evolution (progenitor population drift):

*compare like with like at low z and high z *observe SNe Ia at 1.5<z<3 to probe evolution (Branch et al. 2001; Riess & Livio 2006)

Yun Wang, 1/21/2008

Weak Lensing of SNe Weak Lensing of SNe IaIa

Kantowski, Vaughan, & Branch 1995 Frieman 1997 Wambsganss et al. 1997 Holz & Wald 1998 Metcalf & Silk 1999 Wang 1999

WL of SNe Ia can be modeled by a Universal Probability Distribution for Weak Lensing Magnification (Wang, Holz, & Munshi 2002)

The WL systematic of SNe Ia can be removed by flux averaging (Wang 2000; Wang & Mukherjee 2003)

Δr┴ = DAΔθΔr|| = (c/H)Δz

BAO “wavelength” in transverse direction in slices of z : DA(z)

BAO “wavelength” in radialdirection in slices of z : H(z)

Δr|| = Δr┴ = 148 Mpc = standard ruler

Baryon acoustic oscillations Baryon acoustic oscillations as as

a standard rulera standard rulerBlake & Glazebrook 2003Seo & Eisenstein 2003

Yun Wang, 1/21/2008

Detection of BAO in the SDSS dataDetection of BAO in the SDSS data [Eisenstein et al. 2005]

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DE eq. of state

w(z)=w0+wz

Wang 2006

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Wang 2006

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BAO systematic effectsBAO systematic effects• Galaxy clustering bias (how light traces mass)• Redshift space distortions (artifacts not present in

real space)• Nonlinear gravitational clustering

– small scale information in P(k) is destroyed by cosmic evolution due to mode-coupling (nonlinear modes)

– Intermediate scale P(k) significantly altered in shape (shape is measured cleanly only at k < 0.1h/Mpc at z=0)

(e.g., White 2005; Jeong & Komatsu 2006;

Koehler, Schuecker, & Gebhardt 2007)

Yun Wang, 1/21/2008

Weak Lensing Tomography Weak Lensing Tomography and Cross-Correlation and Cross-Correlation

CosmographyCosmography

Yun Wang, 1/21/2008

• Weak Lensing Tomography:Weak Lensing Tomography: compare observed cosmic shear correlations with theoretical/numerical predictions to measure cosmic large scale structure growth history G(z) and H(z) [Wittman et al. 2000]

• WL Cross-Correlation WL Cross-Correlation CosmographyCosmography measure the relative shear signals of galaxies at different distances for the same foreground mass distribution: gives distance ratios dA(zi)/dA(zj) that can be used to obtain cosmic expansion history H(z) [Jain & Taylor 2003]

Yun Wang, 1/21/2008

Measurements of cosmic shear Measurements of cosmic shear (WL image distortions of a few percent)(WL image distortions of a few percent)

left:top-hat shear variance; right: total shear correlation function. 8=1 (upper); 0.7 (lower). zm=1. [Heymans et al. 2005]

First conclusive detection of cosmic shear was made in 2000.

Yun Wang, 1/21/2008

Cosmological parameter constraints from WLCosmological parameter constraints from WL

L: 8 from analysis of clusters of galaxies (red) and WL (other). [Hetterscheidt et al. (2006)]

R: DE constraints from CFHTLS Deep and Wide WL survey. [Hoekstra et al. (2006)]

Yun Wang, 1/21/2008

WL systematics effectsWL systematics effects• Bias in photometric redshift distribution (< 0.1%

required to avoid significant degradation of DE constraints)

• PSF correction (errors in calibration of the PSF isotropic smearing and correction of PSF anisotropy)

• Biased selection of the galaxy sample• Intrinsic distortion signal (intrinsic alignment of

galaxies)

(e.g., Casertano 2002; King & Schneider 2003; Hirata & Seljak2004; Heymans et. Al. 2006; Huterer et al. 2006)

Yun Wang, 1/21/2008

Clusters as DE probeClusters as DE probe1) Use the cluster number density and its redshift

distribution, as well as cluster distribution on large scales.

2) Use clusters as standard candles by assuming a constant cluster baryon fraction, or use combined X-ray and SZ measurements for absolute distance measurements.

• Large, well-defined and statistically complete samples of galaxy clusters are prerequisites.

(e.g. Haiman, Mohr, Holder 2001; Vikhlinin et al. 2003; Schuecker et al. 2003; Allen et al. 2004; Molnar et al. 2004)

Yun Wang, 1/21/2008

Clusters as DE probeClusters as DE probe• Requirements for future surveys:

– selecting clusters using data from X-ray satellite with high resolution and wide sky coverage

– Multi-band optical and near-IR surveys to obtain photo-z’s for clusters.

• Systematic uncertainties: uncertainty in the cluster mass estimates that are derived from observed properties, such as X-ray or optical luminosities and temperature.

(e.g. Majumdar & Mohr 2003, 2004; Lima & Hu 2004)

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Future ProspectsFuture Prospects

Yun Wang, 1/21/2008

DETF recommendationsDETF recommendations • Aggressive program to explore DE as fully as possible.• DE program with multiple techniques at every stage, at least one

of these is a probe sensitive to the growth of cosmic structure in the form of galaxies and clusters of galaxies.

• DE program in Stage III (near-term) designed to achieve at least a factor of 3 gain over Stage II (ongoing) in the figure of merit.

• DE program in Stage IV (long-term) designed to achieve at least a factor of 10 gain over Stage II in the figure of merit.

• Continued research and development investment to optimize JDEM, LST, and SKA (Stage IV) to address remaining technical questions and systematic-error risks.

• High priority for near-term projects to improve understanding of dominant systematic effects in DE measurements, and wherever possible, reduce them.

• A coherent program of experiments designed to meet the above coals and criteria.

Yun Wang, 1/21/2008

NRC BEPACNRC BEPAC

Recommendation 1Recommendation 1

NASA and DOE should proceed immediately with a competition to select a Joint Dark Energy Mission for a 2009 new start. The broad mission goals in the Request for Proposal should be (1) to determine the properties of dark energy with high precision and (2) to enable a broad range of astronomical investigations. The committee encourages the Agencies to seek as wide a variety of mission concepts and partnerships as possible.

Yun Wang, 1/21/2008

Future Dark Energy SurveysFuture Dark Energy Surveys (an incomplete list)(an incomplete list)

• Essence (2002-2007): 200 SNe Ia, 0.2 < z < 0.7, 3 bands, t ~ 2d • Supernova Legacy Survey (2003-2008): 2000 SNe Ia to z=1• CFHT Legacy (2003-2008): 2000 SNe Ia, 100’s high z SNe, 3 bands, t ~ 15d• ESO VISTA (2005?-?): few hundred SNe, z < 0.5• Pan-STARRS (2006-?): all sky WL, 100’s SNe y, z < 0.3, 6 bands, t = 10d• WiggleZ on AAT using AAOmega (2006-2009): 1000 deg2 BAO, 0.5< z < 1

• ALPACA (?): 50,000 SNe Ia per yr to z=0.8, t = 1d , 800 sq deg WL & BAO with photo-z

• Dark Energy Survey (?): cluster at 0.1<z<1.3, 5000 sq deg WL, 2000 SNe at 0.3<z<0.8

• HETDEX (2010): 200 sq deg BAO, 1.8 < z < 3.• WFMOS on Subaru (?): 2000 sq deg BAO, 0.5<z<1.3 and 2.5<z<3.5

• LSST (2012?): 0.5-1 million SNe Ia y, z < 0.8, > 2 bands, t = 4-7d; 20,000 sq deg WL & BAO with photo-z

• JDEM (2017?): several competing mission concepts [ADEPT, DESTINY, JEDI, SNAP]

• EDEM (2017?): two competing mission concepts [DUNE and SPACE]

Yun Wang, 1/21/2008

Future Dark Energy Space Future Dark Energy Space MissionsMissions

• JDEM (2017?): several mission concepts – ADEPT: BAO (spec-z) and SNe– DESTINY: SNe, WL, and BAO (photo-z)– JEDI: SNe, WL, and BAO (spec-z), – SNAP: SNe, WL, and BAO (photo-z)

• EDEM (2017?): two mission concepts – DUNE: WL, BAO (photo-z)– SPACE: BAO (spec-z) and SNe

Yun Wang, 1/21/2008

How many methods should we How many methods should we use?use?

• The challenge to solving the DE mystery will not be the statistics of the data obtained, but the tight control of systematic effects inherent in the data.

• A combination of three most promising methods (SNe, BAO, WL), each optimized by having its systematics minimized by design, provides the tightest control of systematics.

Yun Wang, 1/21/2008

Joint Efficient Dark-energy Joint Efficient Dark-energy Investigation (JEDI):Investigation (JEDI):

a candidate implementation of JDEM http://jedi.nhn.ou.edu/

Yun Wang, 1/21/2008

JEDI CollaborationJEDI CollaborationPI: Yun Wang (U. of Oklahoma)Deputy PI: Edward Cheng (Conceptual Analytics)

Scientific Steering Committee:Arlin Crotts (Columbia), Tom Roellig (NASA Ames), Ned Wright (UCLA)

SN Lead: Peter Garnavich (Notre Dame), Mark Phillips (Carnegie Observatory)WL Lead: Ian Dell’Antonio (Brown)BAO Lead: Leonidas Moustakas (JPL)

Eddie Baron (U. of Oklahoma) David Branch (U. of Oklahoma)Stefano Casertano (STScI) Bill Forrest (U. of Rochester)Salman Habib (LANL) Mario Hamuy (U. of Chile)Katrin Heitmann (LANL) Alexander Kutyrev (NASA GSFC)John MacKenty (STScI) Craig McMurtry (U. of Rochester)Judy Pipher (U. of Rochester) William Priedhorsky (LANL)Robert Silverberg (NASA GSFC) Volker Springel (Max Planck Insti.)Gordon Squires (Caltech) Jason Surace (Caltech)Max Tegmark (MIT) Craig Wheeler (UT Austin)

JEDI: exploiting 0.8-4 JEDI: exploiting 0.8-4 µµmm “sweet “sweet spot”spot”

Background sky spectrum: Leinert 1998, A&AS, 127, 1

- lowest sky background region within ~0.3-100 - lowest sky background region within ~0.3-100 µµm m wavelengthswavelengths

- rest wavelengths in red/near-IR for redshifts 0 < z < 4- rest wavelengths in red/near-IR for redshifts 0 < z < 4

Yun Wang, 1/21/2008

JEDI: the Power of Three JEDI: the Power of Three Independent MethodsIndependent Methods

Supernovae as standard candles: luminosity distances dL(zi)

Baryon acoustic oscillations as a standard ruler:

cosmic expansion rate H(zi) angular diameter distance dA(zi)

(cosmic structure growth rate fg(z) from the same data)

Weak lensing tomography andcosmography:

cosmic structure growth historyG(z); ratios of dA(zi)/dA(zj)

The three independent methods to probe H(z) [and two independent methods to probe gravity] will provide a powerful cross check, and allow JEDI to place accurate and precise constraints on dark energy.

Yun Wang, 1/21/2008

JEDI Measures H(z) to ≤ 2% accuracy JEDI Measures H(z) to ≤ 2% accuracy using supernovae and baryon acoustic using supernovae and baryon acoustic

oscillations oscillations

Note that the errors go opposite ways in the two methods.

Wang et al.,in preparation(2008)

SPectroscopic All-sky Cosmic Explorer

Andrea Cimatti (UniBO), Massimo Robberto (STScI) & the SPACE Team

http://urania.bo.astro.it/cimatti/space/

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PI: A. Cimatti (University of Bologna, Italy) + co-PI: M. Robberto (STScI, USA)Co-Is (in boldface : coordinator of SPACE Working Groups): Austria :W. Zeilinger (U.Wien); France: E. Daddi (CEA Saclay,), M. Lehnert, F. Hammer (Meudon), O. Le Fevre, J.-P. Kneib, J. G. Cuby, L.

Tresse, R. Grange, M. Saisse (LAM); Germany: S. White, G. Kauffmann, B. Ciardi, G. De Lucia, J. Blaizot (MPA Garching), F. Bertoldi

(U. Bonn), E. Schinnerer, A. Martinez-Sansigre, F. Walter, J. Kurk, J. Steinacker (MPIA Heidelberg); International: P. Rosati, P.

Padovani (ESO); D. Macchetto (ESA); Italy: A. Ferrara (SISSA), A. Franceschini (U. Padova), A. Renzini (INAF OAPD), S. Cristiani, M.

Magliocchetti, E. Pian, F. Pasian, A. Zacchei (INAF OATS), G. Zamorani, M. Mignoli, L. Pozzetti, C. Gruppioni, A. Comastri (INAF

OABO), N. Mandolesi, R. C.Butler, C. Burigana, L. Nicastro, F. Finelli, L. Valenziano, G. Morgante, L. Stringhetti, F. Villa, F. Cuttaia,

E. Palazzi, A. De Rosa, A. Gruppuso, A. Bulgarelli, F. Gianotti, M. Trifoglio, F. Paresce (INAF IASFBO), L. Guzzo, F. Zerbi, E. Molinari,

P. Spanó (INAF Milano), R. Salvaterra (U. Milano), M. Bersanelli (U. Milano), D. Maccagni, B. Garilli, M.

Scodeggio, D. Bottini, P. Franzetti (INAF IASFMI), T. Oliva (Arcetri, TNG); Netherlands: M. Franx, H. Roettgering, M. Kriek (U.

Leiden); Romania: L. Popa (U. Bucharest); Spain: R. Rebolo, M. Zapatero Osorio, M. Balcells (IAC), A. Perez Garrido, A. Díaz Sánchez,

I. Villó Pérez (UPCT, U. Politecnica de Cartagena); Switzerland: H. Shea (École Polytechnique Lausanne); United Kingdom: C. Frenk, C.

Baugh, I. Smail, S. Cole, R. Bower, T. Shanks, M. Ward (U. Durham , Inst. Comp. Cosmology), R. Content, R. Sharples, S. Morris (U.

Durham, Centre for Advanced Instrumentation), J. Silk (U. Oxford), J. Dunlop, R. McLure, M. Cirasuolo (ROE), R. Kennicutt (IoA,

Cambridge), M. Jarvis (U. Hertfordshire);

USA: Y. Wang (U. Oklahoma), X. Fan (U. Arizona), P. Madau (UCSC), M. Stiavelli , I. N. Reid, M. Postman, R. White, S. Casertano, S.

Beckwith (STScI), J. Gardner, M. Clampin, R. Kimble (GSFC), A. Szalay, R. Wyse (JHU), A. Shapley (Princeton), N. Wright (UCLA), M.

Strauss (Princeton), M. Urry (Yale), A. Burgasser (MIT), J. Rayner (Hawaii), B. Mobasher (UC Riverside), M. Di Capua (UMD), L.

Hillenbrand (Caltech), M. Meyer (Steward).

Yun Wang, 1/21/2008

The power of spectroscopic redshifts

spectroscopic z

photometric z withoptimistic σz=0.02(1+z)

Yun Wang, 1/21/2008

SPACE MISSION SUMMARY

Telescope diameter 1.5m

Optical configuration Ritchey-Chrétien

Wavelength range 0.6 - 1.8 m

Optical quality Diffraction limited >0.65m

Pointing stability 0.1” rms/ 30min

Overall mass 1486 kg

Data rate 1.5Mbit/s

Orbit/Launcher L2/Soyuz

Launch date Mid 2017

Mission Duration 5 years

Partners ESA-NASA-European Agencies

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Left: 0.2% systematic assumed in each z bin. Right: 1% systematic assumed in each z bin

Growth rate function & galaxy clusters provideadditional improvements + breaking H(z) degeneracies + test on gravitational theories

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ALPACAALPACA• 8m liquid mirror telescope

• FOV: 2.5 deg diameter

• Imaging=0.3-1m

• 50,000 SNe Ia per yr to z=0.8, 5 bands, t = 1d

• ~1000 (deg)2 WL & BAO with photo-z

Project Scientist: Arlin Crotts

Observatory Scientist: Paul Hickson

Science Advisory Council Chair: Yun Wang

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• 8.4m (6.5m clear aperture) telescope; FOV: 3.5 deg diameter; 0.3-1m

• 106 SNe Ia y, z < 0.8, 6 bands, t = 7d

• 20,000 (deg)2 WL & BAO with photo-z

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Differentiating Differentiating dark energy dark energy

and and modified modified gravitygravity

fg = dln/dlna

= (m-m)/m

Wang (2007)

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ConclusionsConclusions Unraveling the nature of DE is one of the most important

problems in cosmology. Current data (SNe Ia, CMB, and LSS)are consistent with a constant X(z) at 68% confidence. However,the reconstructed X(z) still has large uncertainties at z > 0.5.

DE search methods’ checklist: 1) Supernovae 2) Baryon acoustic oscillations (galaxy redshift survey) 3) Weak lensing 4) Clusters

A combination of different methods is required to achieveaccurate and precise constraints on the time dependence of X(z) and to probe gravity . This will have a fundamental impact on particle physics and cosmology.

Yun Wang, 1/21/2008

What is the fate of the What is the fate of the universe?universe?

Wang & Tegmark, PRL (2004)Wang & Tegmark, PRL (2004)

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DETF DefinitionsDETF Definitions

• DETF figure of merit = 1/[area of 95% C.L. w0-wa error ellipse]

• DETF stages for DE probes:– Stage I: Current knowledge– Stage II: Ongoing projects– Stage III: Near-term, medium-cost projects, – Stage IV: Long-term, high-cost projects (JDEM,

LST, SKA)

Yun Wang, 1/21/2008

Growth history of structure from WLGrowth history of structure from WL

Cosmic shear signal on fixed angular scales as a function of redshift.[Massey et al. (2007)]

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Forecasting of DE constraints from WLForecasting of DE constraints from WL

DUNE: 20,000 sq deg WL survey with zm=1, 1 broad red band, photo-z from ground surveys [Refregier et al. (2006)]

Yun Wang, 1/21/2008

DE constraints from WL depend on the DE constraints from WL depend on the accuracy of photometric redshiftsaccuracy of photometric redshifts

Huterer et al. (2006)

Yun Wang, 1/21/2008

Baryon acoustic Baryon acoustic oscillations as oscillations as

a standard rulera standard rulerBlake & Glazebrook

2003

Seo & Eisenstein 2003

Comparing observed Comparing observed acoustic scales with acoustic scales with expected values expected values (calibrated by CMB) (calibrated by CMB) gives us gives us HH((zz) [radial ) [radial direction] and direction] and DDAA((zz) )

[transverse direction][transverse direction]

Yun Wang, 1/21/2008

Redshift space distortionsRedshift space distortions

Large scale compression

due to linear motions

gives the Kaiser factor

=fg/b,

fg =dlnG/dlna~ (a)0.55

G(z)=(z)/(0)

(a)=m/.

Yun Wang, 1/21/2008 Image credit: V. Springel

z=6

z=2

z=0

f(z) traces how structure grows inside the box gravitation theory. H(z) measures how the box expands with time equation of state w(z)

Models with the same expansion history H(z) but different gravitational theory will have a different growth rate function f(z).Discrepancy between f(z) and H(z) from GR:smoking gun for New Physics. Need both H(z) and f(z) to break possible degeneracies.

Yun Wang, 1/21/2008

SPACE INSTRUMENT PERFORMANCETotal field of view 51’ x 27’ (0.4 sq. degrees)

Nr. and type of DMDs 4 CINEMA chip (2048x1050)

Total nr. of mirrors 8.8 million

Mirror field of view 0.75” x 0.75”

Number of spectra ~ 6,000 simultaneous

Detector Pixel size 0.375” x 0.375”

Dispersing element Prism R~400; 0.8-1.8m

Imaging filters z, J, H, narrow band

Detector HgCdTe 0.4-1.8µm, 2k x 2k

Nr. of detectors 16 (4 mosaics of 2x2 chips)

Detector Temperature ~145 K

QE >75% average

Readout noise 5e-/multiple read

Observing modes Broad- and narrow-band imaging, multi-slit, slitless spectroscopy

Yun Wang, 1/21/2008

Combining ALPACA Dark Energy Combining ALPACA Dark Energy ConstraintsConstraints

The simplest dark energy investigation method sensitivities to estimate are SN Ia standard candles, weak lensing shear and baryon acoustic oscillations. To express dark energy dynamics, we use w = w0 + wa a = w0 + wa /(1+z), where wa describes the redshift change in w. A few points:

If SN Ia method systematics ~ 10%, baryon oscillations are more useful. If ~ 2%, SN are more useful, comparable to weak lensing constraints.Current limits combining CMB anisotropies, LSS and SN Ia constrain w at the 10% level. ALPACA could improve this 5x. Limit on wa would be vital in distinguishing dark energy models.

Corasaniti et al. (2006)

Dataset error on: m w0 wa

SNe (2% syst.+WMAP) 0.03 0.15 1.0SNe+BAO 0.02 0.11 0.65WL 0.02 0.20 0.57SNe+BAO+WL 0.01 0.04 0.16SNe+BAO+WL+Planck 0.003 0.02 0.04Planck only 0.013 0.19 0.94

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ESA-ESO WG recommendationsESA-ESO WG recommendations • Wide-field optical and near-IR imaging survey [WL/CL]

– ESA: satellite with high resolution wide-field optical and near-IR imaging

– ESO: optical multi-color photometry from the ground

– ESO: large spectroscopic survey (>100,000 redshifts over ~10,000 sq deg to calibration of photo-z’s)

• Secure access to an instrument with capability for massive multiplexed deep spectroscopy (several thousand simultaneous spectra over one sq deg) [BAO]

• A supernova survey with multi-color imaging to extend existing samples of z=0.5-1 SNe by an order of magnitude, and improve the local sample of SNe. [SNe]

• Use a European Extremely Large Telescope (ELT) to study SNe at z >1. [SNe]

Yun Wang, 1/21/2008

Understanding SN Ia SpectraUnderstanding SN Ia Spectra

Solid: Type Ia SN 1994D, 3 days before maximum brightness

Dashed: a PHOENIX synthetic spectrum (Lentz, Baron, Branch, Hauschildt 2001, ApJ 557, 266)

Yun Wang, 1/21/2008

Evidence for Dark Evidence for Dark EnergyEnergy

Speeding up of cosmic expansion increases the distance between two galaxies (Milky Way and supernova host galaxy), which would lead to fainter than expected observed supernovae.

Observed supernovae are fainter than expected, so the expansion of the universe must have accelerated.

For convenience, the unknown cause for the For convenience, the unknown cause for the observed acceleration of the cosmic expansion observed acceleration of the cosmic expansion is dubbed dark energy.is dubbed dark energy.

Yun Wang, 1/21/2008

Model Selection Using Bayesian Model Selection Using Bayesian EvidenceEvidence

Bayes theorem: P(M|D)=P(D|M)P(M)/P(D)Bayesian edidence: E=L()Pr()d

:likelihood of the model given the data.Jeffreys interpretational scale of lnE between two models:

lnE<1: Not worth more than a bare mention.1<lnE<2.5: Significant.2.5<lnE<5: Strong to very strong.

5<lnE: Decisive.

SNLS (SNe)+WMAP3+SDSS(BAO):SNLS (SNe)+WMAP3+SDSS(BAO):

Compared to Compared to , , lnlnEE=-1.5=-1.5 for constant for constant wwXX model model

lnlnEE=-2.6=-2.6 for for wwXX(a)=w(a)=w00+w+waa(1-a)(1-a) model modelRelative prob. of three models: 77%, 18%, 5%Relative prob. of three models: 77%, 18%, 5%

Liddle, Mukherjee, Parkinson, & Wang (2006)

Yun Wang, 1/21/2008

Need for a space-based mission in the near-infrared

- Sample selected in the near-IR to mAB ≈ 22-23 : 0<z<2, weak k-corrections,

all galaxy types (including E/S0), stellar mass–selected, less affected by dust extinction

- Sky background is 500-1000 times lower in space

- No OH emission lines, no telluric absorptions

- Near-IR spectroscopy : rest-frame optical strongest features visible at all redshifts, E/S0 galaxies, Lyα up to z ≈ 10+

- Moderate spectral resolution (spec-z efficiency, resolve Hα and [N II])

- Digital Micro Mirrors (DMDs)

Yun Wang, 1/21/2008

Requirements for a cosmological mission

To address the key questions of cosmology (not only Dark Energy !)

Observation of a huge volume of the Universe (> 10,000 deg2 , 0<z<2)

Spectroscopic approach (powerful vs photometric SEDs and photo-z)

Wide-field, high “multiplexing”, high survey speed

Slit spectroscopy (vs slitless) : SNR ≈ 65 times higher

Yun Wang, 1/21/2008

SPACE survey programs

“All-sky” near-infrared imaging & spectroscopic survey of ¾ of the sky (3π sr). Sample selected in H-band (AB<23.0). Random sampling rate of 1/3 ≈ Half-billion galaxies at 0 < z < 2 with spectroscopic redshifts, plus quasars up to z ≈ 12

Deep near-infrared imaging and spectroscopy of 10 deg2 downto H(AB) < 26. About 2 million galaxies and AGN at 2 < z < 10.(90% random sampling rate) + Type Ia Supernovae to z ≈ 2.

Galactic plane survey

Open time for Guest Observer programs

Yun Wang, 1/21/2008

SNe with SPACE

• 4 deg2 Deep Field (H<26) (e.g. within the SPACE Deep Field, 10 deg2)

• Repeated visits of the same field every 7 - 10 days (1 visit = 4 days to cover 4 deg2 )

• Advantage to obtain spectra of all SNe in the field

• Near-IR is crucial : spectra of high-z SNe, less dust extinction

• N ≈ 2300 SNe to z ≈ 2 in about 5 – 7 months spread over 1 year (faster than SNAP)

• Synergy with SN “finder” (e.g. SNAP) would be extremely powerful

• Inclusion of SN program in SPACE will depend on the developments of otherprojects in space and on the ground (e.g. SNAP, CFHT, Pan-STARRS, LSST, …)