Cosmology Results from the WiggleZ Dark Energy Survey

David ParkinsonUniversity of Queensland

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Summary

•Introduction

•What is WiggleZ?

•Cosmology Results

•Baryon Acoustic Oscillations

•Redshift Space Distortions

•Power Spectrum

•Homogeneity

•Conclusions

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WiggleZ Survey• WiggleZ is a spectroscopic

galaxy redshift survey conducted on the AAT

• It covers 1000 square degrees over the southern sky, and has measured the redshift of 250,000 galaxies

• It targets bright, star-forming galaxies at high redshift by using the GALEX satellite to generate a source catalogue

• Observing started in 2006 and finished in January 2011

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The AAT

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The WiggleZ Team• University of Queensland:

Michael Drinkwater, Tamara Davis, David Parkinson, Signe Reimer-Sorensen

• Swinburne: Chris Blake, Carlos Contreras, Warrick Couch, Darren Croton, Karl Glazebrook, Eyal Kazin, Tornado Li, Felipe Marin, Greg Poole, Emily Wisniowski

• AAO: Sarah Brough, Matthew Colless, Mike Pracy, Rob Sharp

• Scott Croom (USyd), Ben Jelliffe (USyd), David Woods (UBC), Kevin Pimblet (Monash), Russell Jurek (ATNF), Rachel Mandelbaum (Princeton)

• Galex Team: Karl Forster, Barry Madore, Chris Martin, Ted Wyder

• RCS2 Team: David Gilbank, Mike Gladders, Howard Yee

• Associate: Berian James (DARK)

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WiggleZ Survey Fields

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Redshifts• GALEX satellite imaging

• UV-selected galaxies

• Medium Imaging Survey extended

• NUV < 22.8

• Optical imaging: r < 22.5

• SDSS (North)

• RCS2 survey on CFHT (South)

• AAOmega fibre spectrograph

• 220-night large project

• Measure 240,000 redshifts

• Star forming galaxies

• Emission line redshifts in short 1-hour exposures

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Results 1: BAO• Before recombination, the

baryons and photons were tightly coupled and behaved as a single photon-baryon fluid.

• Gravity compresses the gas and the pressure restores it, so the fluid can carry acoustic oscillations - sound waves.

• When recombination occurs, the photons and baryons decouple and the sound speed of the fluid drops to zero very quickly.

• The oscillations are ‘frozen’ into the distribution of matter, and can be detected through galaxy redshift surveys

rarefaction = cold spot

compression = hot spot

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2-pt correlation function

• The χ2 for the best fitting model was 14.9 (17 bins and 3 free parameters) whereas for the no-wiggles model it was 25.

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• Using the correlation function or Power Spectrum the BAO feature allows us to measure the angle-averaged distance, DV.

• The degeneracy direction between DV and Ωmh2 depends on the statistic used to measure the feature

Standard ruler

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Interpretation• BAO measurements are normally reported as either:

• A(z): the `acoustic parameter’ (from Eisenstein et al 2005)

• dz: the sound horizon ratio, where rs is the sound horizon at the baryon drag epoch, zd

• Rz: the CMB standard ruler ratio

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Distance measurements

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DA vs DL

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Curvature

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Curvature

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Equation of state

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Equation of state

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Curvature+w

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Time-evolution of w

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Results 2: z-space distortions

• The motions of galaxies are perturbed by the local gravitational field

• The Power spectrum/correlation function in the line of sight is distorted relative to the transverse direction

• Assuming these motions are generated by matter perturbations, we can measure the growth of structure

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Velocity field Theory• The redshift space over-density is given by

where θ is the FT of the divergence of the velocity field.

• The linear power spectrum is therefore given by

• Assuming the velocity field is generated under linear perturbation theory

where f is the rate of growth of structure

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2D Power Spectra

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Growth of structure

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AP effect• The Alcock-Paczynski effect

states that the ratio of observed angular size (Δθ) to radial size (Δz) varies with cosmology

• The intrinsic size does not need to be known to measure the observable

• The distribution of galaxies should be isotropic in radial and tangential directions, and can be used to measure the AP effect, but it is degenerate with redshift-space distortions

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AP/Growth measurements

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H(z) reconstruction

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Results 3: P(k)• We can predict

the matter power spectrum for a given cosmology and so compare the prediction to the observations to test cosmological models

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Cut-off scale

• Notice the agreement with Planck.

• Only kmax=0.3 h Mpc-1 deviates significantly.

• Our choice of kmax=0.2 h Mpc-1 for the analysis is conservative as the extension to kmax=0.25 h Mpc-1 is still consistent with the more linear results.

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Neutrino MassRiemer-Sørensen, Parkinson & DavisarXiv:1306.4153

• Planck+BAO: Σmν < 0.30 eV

• Planck+BAO+WiggleZ: Σmν < 0.15 eV

• 50% improvement on Planck+BAO alone.

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•! Fractal dimensions are a way of

quantifying clustering

•! Correlation dimension D2(r): related to 2-

point correlation function. Based on the

mean value N(<r) of the number of

galaxies within distance r of a galaxy

•! From this, D2 is defined

N(< r)! rD2

!

D2(r) "d lnN(< r)

d ln r

Fractal (correlation) dimension D2(r)

Image: hubblesite.org

D2=3 for a

homogeneous

distribution

Results 4: Homogeneity• Fractal dimensions are a way

of quantifying clustering

• Correlation dimension D2(r): related to 2-point correlation function. Based on the mean value N(<r) of the number of galaxies within distance r of a galaxy

• From this, D2 is defined

Scrimgeour et al (2012)

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•! Fractal dimensions are a way of

quantifying clustering

•! Correlation dimension D2(r): related to 2-

point correlation function. Based on the

mean value N(<r) of the number of

galaxies within distance r of a galaxy

•! From this, D2 is defined

N(< r)! rD2

!

D2(r) "d lnN(< r)

d ln r

Fractal (correlation) dimension D2(r)

Image: hubblesite.org

D2=3 for a

homogeneous

distribution

Results 4: Homogeneity• Fractal dimensions are a way

of quantifying clustering

• Correlation dimension D2(r): related to 2-point correlation function. Based on the mean value N(<r) of the number of galaxies within distance r of a galaxy

• From this, D2 is defined

Scrimgeour et al (2012)

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•! Fractal dimensions are a way of

quantifying clustering

•! Correlation dimension D2(r): related to 2-

point correlation function. Based on the

mean value N(<r) of the number of

galaxies within distance r of a galaxy

•! From this, D2 is defined

N(< r)! rD2

!

D2(r) "d lnN(< r)

d ln r

Fractal (correlation) dimension D2(r)

Image: hubblesite.org

D2=3 for a

homogeneous

distribution

Results 4: Homogeneity• Fractal dimensions are a way

of quantifying clustering

• Correlation dimension D2(r): related to 2-point correlation function. Based on the mean value N(<r) of the number of galaxies within distance r of a galaxy

• From this, D2 is defined

Scrimgeour et al (2012)

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Scale of HomogeneityD2(r)

Scrimgeour et al. (2012), submitted

0.1<z<0.3

0.7<z<0.9 0.5<z<0.7

0.3<z<0.5

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Conclusions• WiggleZ is a large-area galaxy redshift survey carried out on the AAT that

covered 1000 deg2 and surveyed ~250,000 galaxies

• WiggleZ has detected the BAO feature in three different redshift bins, and used it to measure the distance-redshift relation (DV) to an accuracy of 9.1% (0.2 < z < 0.6), 6.5% (0.4 < z < 0.8) and 6.4% (0.6 < z < 1.0).

• By combining BAO with WMAP and SNIa, we are able to tightly constrain curvature and a constant equation of state simultaneously w = −1.063 ± 0.094 and Ωk = −0.0061 ± 0.0070.

• We have measured the growth of structure to a precision of about 10% in four redshifts bins using redshift-space distortions of the galaxy power spectra

• We have modelled the matter power spectrum, and combined it with other cosmological datasets to constrain the (total) mass of neutrinos to be less than 0.15 eV

• We have shown the the Universe does transition to homogeneity, at a scale of about 70-80 Mpc (depending on redshift)

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Extra slides

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You Are Here• The universe is composed

of 4% baryons, 22% dark matter, and 74% dark energy.

• Where does the dark energy come from? Is it:

• Cosmological constant (Λ)

• Quintessence (Q)

• Modification of gravity

• No current evidence for time variation of DE (yet!)

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Probing the Dark Energy

•Luminosity Distances, dL (e.g. SN-Ia)

•Angular Diameter Distances, dA (e.g. transverse BAO)

•Direct Expansion rate data, H(z) (e.g. radial BAO, cosmic clocks)

•Growth of Structure, g(z) (e.g. Weak Lensing, ISW)

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Selection function

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Power Spectrum fitting• The advantage of WiggleZ lies in being able to fit down to

small scales, k=0.3. But this requires modelling of the non-linear dark matter evolution and pair-wise velocity damping

• There are a number of approaches available:

• Halofit (Peacock & Smith 2000) - implemented in CosmoMC already

• Empirical damping (Peacock & Dodds 1994)

• Jennings fitting formula (Jennings, Baugh, Pascoli 2010)

• SDSS approach (Reid et al 2010)

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GiggleZ approach• The Reid et al approach considered three effects

to model the non-linear P(k)

• BAO damping (Gaussian smoothing of BAO peak)

• Non-linear structure growth (Halofit applied to smooth component)

• Halo bias & evolution with redshift (calibrated from simulations)

• The GiggleZ approach applies the Reid et al approach, but using our own simulations

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Power spectrum models

0.01 0.10 1.00Inverse scale, k [h/Mpc]

102

103

104

105

Pow

er, P

(k)

0.01 0.10 1.00Inverse scale, k [h/Mpc]

102

103

104

105

Pow

er, P

(k)

HalofitLinear

Jennings dampingJennings zero damping

Pairwise velocity dampingGiggleZ model

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Testing models

123456

!2 Gig

gleZ

/dof

0.1 0.2 0.3 0.4 0.5kmax [h Mpc−1]

01

2

3

45

(!2 G

iggl

eZ−!

2 best)/d

of

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ΛCDM

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Gamma

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Gamma

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f(R)

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f(R)

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f(R)

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DGP

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