Joint Galaxy-Lensing Observables and the Dark Energy

Abstract

Deep multi-color galaxy surveys with photometric redshifts will provide a large number of two-point correlation observables: galaxy-galaxy angular correlations, galaxy-shear cross correlations, and shear-shear correlations between all redshifts. These observables can potentially enable a joint determination of the dark energy dependent evolution of the dark matter and distances as well as the relationship between galaxies and dark matter halos. With recent CMB determinations of the initial power spectrum, a measurement of the mass clustering at even a_single_ redshift will constrain a well-specified combination of dark energy parameters in a flat universe; we provide convenient fitting formulae for such studies. The combination of galaxy-shear and galaxy-galaxy correlations can determine this amplitude at_multiple_ redshifts. We illustrate this ability in a description of the galaxy clustering with 5 free functions of redshift which can be fitted from the data. The galaxy modeling is based on a mapping onto halos of the same abundance that models a flux-limited selection. In this context, a 4000 deg2 galaxy-lensing survey can achieve a_statistical_ precision of sigma(Omega_DE)=0.005 for the dark energy density, sigma(w_DE)=0.02 and sigma(w_a)=0.17 for its equation of state and evolution, evaluated at dark energy matter equality z~0.4, as well as constraints on the 5 halo functions out to z=1. More importantly, a joint analysis can make dark energy constraints robust against systematic errors in the shear-shear correlation and halo modeling.