Improving measurements of H(z) and DA (z) by analysing clustering anisotropies

The baryonic acoustic feature in galaxy clustering is a promising tool for constraining the nature of the cosmic acceleration, through measurements of expansion rates H and angular diameter distances DA. Angle-averaged measurements of clustering yield constraints on the quantity DA²/H. However, to break the degeneracy between these two parameters one must measure the anisotropic clustering as a function of both line-of-sight (radial) and transverse separations. Here we investigate how to most effectively do so, using analytic techniques and mock catalogues. In particular, we examine multipole expansions of the correlation function and introduce 'clustering wedges'ξ (Δμ, s), where μ=s∥/s and s∥ is the radial component of separation s. Both techniques allow strong constraints on H and DA, as expected. The radial wedges strongly depend on H and the transverse wedges are sensitive to DA. When analysing the full shape of ξ, we find similar constraints when using the clustering wedges and the monopole-quadrupole pair. We find additional improvement when using the hexadecapole, as previously mentioned in the literature. Our findings here demonstrate that wedge statistics provide a practical alternative technique to multipoles, which should be useful to test systematics and will provide comparable constraints.