Large-scale homogeneity vs. small-scale inhomogeneity: testing ΛCDM with large scale structure



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14040141

Abstract

The most fundamental assumption of the standard cosmological model (LambdaCDM) is that the Universe is homogeneous on large scales. This is not true on small scales, and some studies suggest that galaxies follow a fractal distribution up to very large scales (~200 h-1 Mpc or more), whereas ΛCDM predicts homogeneity at ~100 h-1 Mpc. We have tested this using the WiggleZ Dark Energy Survey, a UV-selected spectroscopic survey of ~200,000 luminous blue galaxies up to z=1, with the Anglo-Australian Telescope. The large volume and depth of WiggleZ allows us to probe the transition of the galaxy distribution to homogeneity on large scales, and see if this is consistent with a ΛCDM prediction. Conversely, the properties of small-scale inhomogeneities are an important probe of cosmology. The growth of primordial density perturbations to the large-scale structures present in the Universe today depends on the interplay between cosmic expansion and gravitational interaction. We measure the "bulk flow", or dipole of the velocity field, using the 6dF Galaxy Survey, and show how this can be used as an independent probe of cosmology.