Cosmology Results from the WiggleZ Dark Energy SurveyGreg Poole, Emily Wisniowski ... • Gravity...
Transcript of Cosmology Results from the WiggleZ Dark Energy SurveyGreg Poole, Emily Wisniowski ... • Gravity...
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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