Robust constraints on dark energy and gravity from galaxy clustering data

Galaxy clustering data provide a powerful probe of dark energy. We examine how the constraints on the scaled expansion history of the Universe, x h (z) = H(z)s (with s denoting the sound horizon at the drag epoch), and the scaled angular diameter distance, x d (z) = D A (z)/s, depend on the methods used to analyse the galaxy clustering data. We find that using the observed galaxy power spectrum, P obs g (k), x h (z) and x d (z) are measured more accurately and are significantly less correlated with each other, compared to using only the information from the baryon acoustic oscillations (BAO) in P obs g (k). Using the {x h (z), x d (z)} from P obs g (k) gives a Dark Energy Task Force (DETF) dark energy figure of merit (FoM) approximately a factor of 2 larger than using the {x h (z), x d (z)} from BAO only; this provides a robust conservative method to go beyond BAO only in extracting dark energy information from galaxy clustering data.