Using the topology of large-scale structure in the WiggleZ Dark Energy Survey as a cosmological standard ruler

Abstract

We present new and accurate measurements of the cosmic distance–redshift relation, spanning 0.2 < z < 1, using the topology of large-scale structure as a cosmological standard ruler. Our results derive from an analysis of the Minkowski functionals of the density field traced by the WiggleZ Dark Energy Survey. The Minkowski functionals are a set of statistics which completely describe the topological nature of each isodensity surface within the field, as a function of the density value. Given the shape of the underlying matter power spectrum, measured by fluctuations in the cosmic microwave background radiation, the expected amplitudes of the Minkowski functionals are specified as an excursion set of a Gaussian random field, with minimal non-Gaussian corrections for the smoothing scales ≥10 h−1 Mpc considered in this analysis. The measured amplitudes then determine the cosmic distance DV(z), which we obtain with 3–7 per cent accuracies in six independent redshift slices, with the standard ruler originating in the known curvature of the model power spectrum at the smoothing scale. We introduce a new method for correcting the topological statistics for the sparse-sampling of the density field by the galaxy tracers, and validate our overall methodology using mock catalogues from N-body simulations. Our distance measurements are consistent with standard models which describe the cosmic expansion history, and with previous analyses of baryon acoustic oscillations (BAOs) detected by the WiggleZ Survey, with the topological results yielding a higher distance precision by a factor of 2. However, the full redshift-space power-spectrum shape is required to recover the topological distances, in contrast to the preferred length scale imprinted by BAOs, which is determined by simpler physics.