The WiggleZ Dark Energy Survey: testing the cosmological model with baryon acoustic oscillations at z=0.6

TL;DR

This study detects baryon acoustic oscillations at the highest observed redshift to date ($z=0.6$) using 132,509 WiggleZ emission-line galaxies, employing the correlation function, power spectrum, and a band-filtered estimator to robustly measure the BAO scale. By modeling quasi-linear damping, non-linear growth, and scale-dependent bias, the authors extract the dilation scale $D_V$ and distilled BAO parameters, notably the acoustic parameter $A(z)$ with $A(0.6)=0.452\pm0.018$, and demonstrate consistency across clustering statistics. The WiggleZ results, when combined with CMB priors and SNe, yield tight cosmological constraints, preferring a flat $\Lambda$CDM model with $\Omega_m\approx0.29$ and $w\approx-1$, while also providing evidence for cosmic acceleration through purely geometric BAO distance ratios ($D_V(0.6)/D_V(0.2)$). The analysis shows a ~5%-level distance measurement at $z=0.6$, improves constraints on $w$ by ~30-50% relative to BAO data alone, and confirms the utility of BAO as a robust, cross-checkable probe of dark energy and cosmic expansion history. Future completion of WiggleZ data promises even tighter constraints and allows tangential/radial BAO separation for enhanced cosmological tests.

Abstract

We measure the imprint of baryon acoustic oscillations (BAOs) in the galaxy clustering pattern at the highest redshift achieved to date, z=0.6, using the distribution of N=132,509 emission-line galaxies in the WiggleZ Dark Energy Survey. We quantify BAOs using three statistics: the galaxy correlation function, power spectrum and the band-filtered estimator introduced by Xu et al. (2010). The results are mutually consistent, corresponding to a 4.0% measurement of the cosmic distance-redshift relation at z=0.6 (in terms of the acoustic parameter "A(z)" introduced by Eisenstein et al. (2005) we find A(z=0.6) = 0.452 +/- 0.018). Both BAOs and power spectrum shape information contribute toward these constraints. The statistical significance of the detection of the acoustic peak in the correlation function, relative to a wiggle-free model, is 3.2-sigma. The ratios of our distance measurements to those obtained using BAOs in the distribution of Luminous Red Galaxies at redshifts z=0.2 and z=0.35 are consistent with a flat Lambda Cold Dark Matter model that also provides a good fit to the pattern of observed fluctuations in the Cosmic Microwave Background (CMB) radiation. The addition of the current WiggleZ data results in a ~ 30% improvement in the measurement accuracy of a constant equation-of-state, w, using BAO data alone. Based solely on geometric BAO distance ratios, accelerating expansion (w < -1/3) is required with a probability of 99.8%, providing a consistency check of conclusions based on supernovae observations. Further improvements in cosmological constraints will result when the WiggleZ Survey dataset is complete.

Figures (20)

• Figure 1: The probability distribution of galaxy redshifts in each of the WiggleZ regions used in our clustering analysis, together with the combined distribution. Differences between individual regions result from variations in the galaxy colour selection criteria depending on the available optical imaging (Drinkwater et al. 2010).
• Figure 2: The combined redshift-space correlation function $\xi(s)$ for WiggleZ survey regions, plotted in the combination $s^2 \, \xi(s)$ where $s$ is the co-moving redshift-space separation. The best-fitting clustering model (varying $\Omega_{\rm m} h^2$, $\alpha$ and $b^2$) is overplotted as the solid line. We also show as the dashed line the corresponding "no-wiggles" reference model, constructed from a power spectrum with the same clustering amplitude but lacking baryon acoustic oscillations.
• Figure 3: The amplitude of the cross-correlation $C_{ij}/\sqrt{C_{ii} C_{jj}}$ of the covariance matrix $C_{ij}$ for the correlation function measurement plotted in Figure \ref{['figxifit']}, determined using lognormal realizations.
• Figure 4: The scale-dependent correction to the non-linear real-space dark matter correlation function for haloes with maximum circular velocity $V_{\rm max} \approx 125$ km s$^{-1}$, which possess the same amplitude of large-scale clustering as WiggleZ galaxies. The green line is the ratio of the real-space halo correlation function to the real-space non-linear dark matter correlation function. The red line is the ratio of the redshift-space halo correlation function to the real-space halo correlation function. The black line, the product of the red and green lines, is the scale-dependent bias correction $B(s)$ which we fitted with the model of Equation \ref{['eqscaledep']}, shown as the dashed black line. The blue line is the ratio of the real-space non-linear to linear correlation function.
• Figure 5: Measurements of the distance-redshift relation using the BAO standard ruler from LRG samples (Eisenstein et al. 2005, Percival et al. 2010) and the current WiggleZ analysis. The results are compared to a fiducial flat $\Lambda$CDM cosmological model with matter density $\Omega_{\rm m} = 0.27$.