The WiggleZ Dark Energy Survey: mapping the distance-redshift relation with baryon acoustic oscillations

TL;DR

This work delivers a comprehensive BAO analysis by combining WiggleZ, 6dFGS, and SDSS-LRG data to map the distance-redshift relation from z ≈ 0.1 to 0.73 and to six distance-redshift points. Through quasi-linear BAO modelling and two complementary templates, it extracts robust measurements of D_V, A(z), and d_z, achieving a stacked BAO detection at 4.9σ relative to a zero-peak model. Joint cosmological fits with SNe and CMB data favor a flat Universe with a cosmological constant, yielding w ≈ -1 and negligible curvature (Ω_k ≈ 0). The results provide a stringent, cross-validated benchmark for dark-energy constraints and set a baseline for upcoming Planck and BOSS analyses.

Abstract

We present measurements of the baryon acoustic peak at redshifts z = 0.44, 0.6 and 0.73 in the galaxy correlation function of the final dataset of the WiggleZ Dark Energy Survey. We combine our correlation function with lower-redshift measurements from the 6-degree Field Galaxy Survey and Sloan Digital Sky Survey, producing a stacked survey correlation function in which the statistical significance of the detection of the baryon acoustic peak is 4.9-sigma relative to a zero-baryon model with no peak. We fit cosmological models to this combined baryon acoustic oscillation (BAO) dataset comprising six distance-redshift data points, and compare the results to similar fits to the latest compilation of supernovae (SNe) and Cosmic Microwave Background (CMB) data. The BAO and SNe datasets produce consistent measurements of the equation-of-state w of dark energy, when separately combined with the CMB, providing a powerful check for systematic errors in either of these distance probes. Combining all datasets we determine w = -1.03 +/- 0.08 for a flat Universe, consistent with a cosmological constant model. Assuming dark energy is a cosmological constant and varying the spatial curvature, we find Omega_k = -0.004 +/- 0.006.

Figures (18)

• Figure 1: Measurements of the galaxy correlation function $\xi(s)$, combining different WiggleZ survey regions, for the redshift ranges $0.2 < z < 0.6$, $0.4 < z < 0.8$, $0.6 < z < 1.0$ and $0.2 < z < 1.0$, plotted in the combination $s^2 \, \xi(s)$ where $s$ is the co-moving redshift-space separation. The best-fitting clustering models in each case, varying the parameters $\Omega_{\rm m} h^2$, $\alpha$, $\sigma_v$ and $b^2$ as described in Section \ref{['secmod']}, are overplotted as the solid lines. Significant detections of the baryon acoustic peak are obtained in each separate redshift slice.
• Figure 2: The amplitude of the cross-correlation $C_{ij}/\sqrt{C_{ii} C_{jj}}$ of the covariance matrix $C_{ij}$ for the combined WiggleZ correlation function measurements for the redshift ranges $0.2 < z < 0.6$, $0.4 < z < 0.8$, $0.6 < z < 1.0$ and $0.2 < z < 1.0$, determined using lognormal realizations.
• Figure 3: Probability contours of the physical matter density $\Omega_{\rm m} h^2$ and scale distortion parameter $\alpha$ obtained by fitting to the WiggleZ survey combined correlation function in four redshift ranges $0.2 < z < 0.6$, $0.4 < z < 0.8$, $0.6 < z < 1.0$ and $0.2 < z < 1.0$. The heavy dashed and dotted lines are the degeneracy directions which are expected to result from fits involving respectively just the acoustic peak, and just the shape of a pure CDM power spectrum. The heavy dash-dotted line represents a constant value of the acoustic "A" parameter defined by Equation \ref{['eqaz']}, which is the parameter best-measured by the WiggleZ correlation function data. The solid circle represents the location of our fiducial cosmological model. The contour level in each case encloses regions containing $68.27\%$ of the total likelihood.
• Figure 4: These panels illustrate the correlations between the scale distortion parameters $\alpha$ fitted to correlation functions for three overlapping WiggleZ redshift slices using 400 lognormal realizations. The red ellipses represent the derived correlation coefficients between these measurements.
• Figure 5: Measurement of the galaxy correlation function $\xi(s)$ from a GiggleZ redshift-space halo subset at $z=0.6$, chosen to possess a similar large-scale clustering amplitude to the WiggleZ galaxies at that redshift. We plot the correlation function in the combination $s^2 \, \xi(s)$ where $s$ is the co-moving redshift-space separation, and compare the result to the WiggleZ correlation function for the redshift range $0.4 < z < 0.8$. The best-fitting clustering model to the GiggleZ measurement, varying the parameters $\Omega_{\rm m} h^2$, $\alpha$, $\sigma_v$ and $b^2$ as described in Section \ref{['secmod']}, is overplotted as the solid line.