dark side of the universe n.
Skip this Video
Download Presentation
Dark Side of the Universe

Loading in 2 Seconds...

play fullscreen
1 / 72

Dark Side of the Universe - PowerPoint PPT Presentation

  • Uploaded on

Dark Side of the Universe. Yun Wang STScI, January 21, 2008. beware of the dark side … Master Yoda. Outline. Dark energy: introduction and current constraints Observational methods for dark energy search Future prospects.

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
Download Presentation

PowerPoint Slideshow about 'Dark Side of the Universe' - cheri

Download Now An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
dark side of the universe
Dark Side of the Universe

Yun Wang

STScI, January 21, 2008


beware of the dark side …

Master Yoda

Yun Wang, 1/21/2008

  • 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 dark energy?We infer its existence via its influence on the expansion history of the universe.

Yun Wang, 1/21/2008


First Evidence for Dark Energy in the Hubble Diagrams of Supernovae [dL(z)] (Riess et al. 1998, Schmidt et al. 1998, Perlmutter et al. 1999)

Yun Wang, 1/21/2008

alternative analysis of first evidence
Alternative 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


Data favor q0 <0: cosmic acceleration

Yun Wang, 1/21/2008

Wang & Tegmark 2005

Yun Wang, 1/21/2008

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

1+z = 1/a

z: cosmological redshift

a: cosmic scale factor


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


(Wang & Mukherjee 2007)

model independent constraints on dark energy as proposed by wang garnavich 2001
Model-independent constraints on dark energy(as proposed by Wang & Garnavich 2001)

Wang & Mukherjee (2007)

Yun Wang, 1/21/2008

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

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

Yun Wang, 1/21/2008

some candidates for dark energy
Some Candidates for Dark Energy

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 & Raval1999)

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 energy
How We Probe Dark Energy
  • Cosmic expansion history H(z) or DE density X(z):

tells 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 fg(z), or growth history G(z):

tells us whether general relativity is modified

fg(z)=dln/dlna, G(z)=(z)/(0)


Yun Wang, 1/21/2008

observational methods for dark energy search
Observational Methods for Dark Energy Search
  • SNe Ia (Standard Candles): method through which DE has been discovered; independent of clustering of matter, probes H(z)
  • 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-Correlation Cosmography: probes growth factor G(z), and H(z)
  • Galaxy Cluster Statistics: probes H(z)

Yun Wang, 1/21/2008

supernovae as standard candles
Supernovae 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

brightness and the redshift of SNe Ia

gives dL(z), hence H(z)

Yun Wang, 1/21/2008

spectral signature of sne ia
Spectral Signature of SNe Ia

Primary feature: Si II 6355 at rest=6150Å

Secondary feature: Si II 4130 dip blueshfted to 4000Å

SN Ia 1999ff (z=0.455):

a: Ca II H and K absorption

b: Si II 4130 dip blueshfted to 4000Å

c: blueward shoulder of Fe II 4555

d: Fe II 4555 and/or Mg II 4481

e: Si III 4560

i: Si II 5051

SN IIb 1993J: double peak centered just

blueward of 4000Å, due to Ca II H and K

absorption at 3980Å due to blueshufted

H, but not similar to Ia redward of


[Coil et al. 2000, ApJ, 544, L111]

Yun Wang, 1/21/2008

theoretical understanding of sne ia
Theoretical understanding of SNe Ia

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 ia
Calibration of SNe Ia

Phillips 1993

Riess, Press, & Kirshner 1995

Brighter SNe Ia

decline more slowly

  • make a correction

to the brightness based

on the decline rate.

26 SNe Ia with

Bmax-Vmax  0.20 from

the Calan/Tololo sample

[Hamuy et al. 1996,

AJ, 112, 2398]

Yun Wang, 1/21/2008

getting the most distant sne ia
Getting the most distant SNe Ia:

critical for measuring the evolution in dark energy density:

Wang & Lovelave (2001)

Yun Wang, 1/21/2008

ultra deep supernova survey
Ultra Deep Supernova Survey

To determine whether SNe Ia are good cosmological

standard candles, we need to nail the systematic

uncertainties (luminosity evolution, gravitational

lensing, dust). This will require at least hundreds of

SNe Ia at z>1. This can be easily accomplished by doing

an ultra deep supernova survey using a dedicated

telescope, which can be used for other things

simultaneously (weak lensing, gamma ray burst

afterglows, etc).

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

Yun Wang, 1/21/2008

sne ia as cosmological standard candles
SNe Ia as Cosmological Standard Candles

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 ia
Weak Lensing of SNe Ia

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)

Yun Wang, 1/21/2008

baryon acoustic oscillations as a standard ruler
Baryon acoustic oscillations as a standard ruler

Δr|| = Δr┴ = 148 Mpc = standard ruler

Δr┴ = DAΔθ

Δr|| = (c/H)Δz

Blake & Glazebrook 2003

Seo & Eisenstein 2003

BAO “wavelength” in transverse

direction in slices of z : DA(z)

BAO “wavelength” in radial

direction in slices of z : H(z)

DE eq. of state


Wang 2006

Yun Wang, 1/21/2008

Wang 2006

Yun Wang, 1/21/2008

bao systematic effects
BAO 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: 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 Cosmography 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 wl image distortions of a few percent
Measurements of cosmic shear (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 wl
Cosmological 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 effects
WL 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 probe
Clusters as DE probe

1) 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 probe1
Clusters 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)

Yun Wang, 1/21/2008

future prospects
Future Prospects

Yun Wang, 1/21/2008

detf recommendations
DETF 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 bepac

Recommendation 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 surveys an incomplete list
Future Dark Energy Surveys(an incomplete list)
  • Essence (2002-2007): 200 SNe Ia, 0.2 < z < 0.7, 3 bands, Dt ~ 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, Dt ~ 15d
  • ESO VISTA (2005?-?): few hundred SNe, z < 0.5
  • Pan-STARRS (2006-?): all sky WL, 100’s SNe y-1, z < 0.3, 6 bands, Dt = 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, Dt = 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-1, z < 0.8, > 2 bands, Dt = 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 missions
Future Dark Energy Space Missions
  • 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 use
How many methods should we 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 investigation jedi
Joint Efficient Dark-energy Investigation (JEDI):

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

Yun Wang, 1/21/2008

jedi collaboration
JEDI Collaboration

PI: 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)

Yun Wang, 1/21/2008

jedi exploiting 0 8 4 m sweet spot

- lowest sky background region within ~0.3-100 µm wavelengths

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

JEDI: exploiting 0.8-4 µm “sweet spot”

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

jedi the power of three independent methods
JEDI: the Power of Three Independent 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 and


cosmic structure growth history

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

Note that the errors

go opposite ways in

the two methods.

Wang et al.,

in preparation


Yun Wang, 1/21/2008



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



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 PolytechniqueLausanne); 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 with

optimistic σz=0.02(1+z)

Yun Wang, 1/21/2008


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

Growth rate function & galaxy clustersprovide

additional improvements + breaking H(z) degeneracies + test on gravitational theories

Yun Wang, 1/21/2008

  • 8m liquid mirror telescope
  • FOV: 2.5 deg diameter
  • Imaging l=0.3-1mm
  • 50,000 SNe Ia per yr to z=0.8, 5 bands, Dt = 1d
  • ~1000 (deg)2 WL & BAO with photo-z

Project Scientist: Arlin Crotts

Observatory Scientist: Paul Hickson

Science Advisory Council Chair: Yun Wang

Yun Wang, 1/21/2008

8.4m (6.5m clear aperture) telescope; FOV: 3.5 deg diameter; 0.3-1mm
  • 106 SNe Ia y-1, z < 0.8, 6 bands, Dt = 7d
  • 20,000 (deg)2 WL & BAO with photo-z

Yun Wang, 1/21/2008

differentiating dark energy and modified gravity
Differentiating dark energy and modified gravity

fg = dln/dlna

 = (m-m)/m

Wang (2007)

Yun Wang, 1/21/2008

  • 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 achieve

accurate 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

detf definitions
DETF 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 wl
Growth history of structure from WL

Cosmic shear signal on fixed angular scales as a function of redshift.

[Massey et al. (2007)]

Yun Wang, 1/21/2008

forecasting of de constraints from wl
Forecasting 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 accuracy of photometric redshifts
DE constraints from WL depend on the accuracy of photometric redshifts

Huterer et al. (2006)

Yun Wang, 1/21/2008

baryon acoustic oscillations as a standard ruler1
Baryon acoustic oscillations as a standard ruler

Blake & Glazebrook 2003

Seo & Eisenstein 2003

Comparing observed acoustic scales with expected values (calibrated by CMB) gives us H(z) [radial direction] and DA(z) [transverse direction]

Yun Wang, 1/21/2008

redshift space distortions
Redshift space distortions

Large scale compression

due to linear motions

gives the Kaiser factor


fg =dlnG/dlna~ (a)0.55



Yun Wang, 1/21/2008


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

Image credit: V. Springel

combining alpaca dark energy constraints
Combining ALPACA Dark Energy Constraints

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 1.0

SNe+BAO 0.02 0.11 0.65

WL 0.02 0.20 0.57

SNe+BAO+WL 0.01 0.04 0.16

SNe+BAO+WL+Planck 0.003 0.02 0.04

Planck only 0.013 0.19 0.94

Yun Wang, 1/21/2008

esa eso wg recommendations
ESA-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 spectra
Understanding 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 energy
Evidence for Dark Energy

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

observed acceleration of the cosmic expansion

is dubbed dark energy.

Yun Wang, 1/21/2008

model selection using bayesian evidence
Model Selection Using Bayesian Evidence

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.


Compared to , lnE=-1.5for constant wX model

lnE=-2.6for wX(a)=w0+wa(1-a) model

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 (3πsr). 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 deg2down

to 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 other
  • projects in space and on the ground (e.g. SNAP, CFHT, Pan-STARRS, LSST, …)

Yun Wang, 1/21/2008