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

Abstract

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 D_A. Angle-averaged measurements of clustering yield constraints on the quantity D_A^2/H. However, to break the degeneracy between these two parameters one must measure the anisotropic correlation function 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 as well as "clustering wedges" xi(Delta mu, s), where mu = s_||/s and s_|| is the radial component of separation s. Both techniques allow strong constraints on H and D_A, as expected. The radial wedges strongly depend on H and the transverse wedges are sensitive to D_A. Analyses around the region of the acoustic peak constrain H ~20% better when using the wedge statistics than when using the monopole-quadrupole combination. However, we show that the hexadecapole allows substantially stronger constraints than the monopole and quadrupole alone. Our findings here demonstrate that wedge statistics provide a practical alternative technique to multipoles, that should be useful to test systematics and will provide comparable or better constraints. Finally, we predict the constraints from galaxy clustering that will be possible with a completed version of the ongoing Baryonic Oscillation Spectroscopic Survey.