Optimising large galaxy surveys for ISW detection

We investigate the potential of next-generation surveys of the cosmic microwave background and large-scale structure, to constrain the nature of dark energy, by means of the cross-correlation of the Integrated Sachs-Wolfe effect with the galaxy distribution. We first complete a signal-to-noise analysis to decide the most appropriate properties of a survey required to detect the correlated signal at a significance level of higher than 4 sigma. We find that more than 35% of the sky should be covered, the galaxy distribution should be probed out to a median redshift higher than 0.8, and the number of galaxies detected should be higher than a few per squared arcmin. We then consider in particular forthcoming surveys DUNE, LSST, SNAP, PanSTARRS. We independently compute the constraints that the DUNE survey can place on the nature of dark energy, by means of different parametrisations of its equation of state, using a standard Fisher matrix analysis. We confirm that, with respect to limits placed by pure CMB, cross-correlation constraints can help to break the degeneracies between dark energy and cosmological parameters. The strength of the constraints is not, of course, independent of the dark-energy model. The constraints are complementary to, despite being weaker than, some other probes of dark energy such as gravitational weak-lensing, because they are sensitive to the high-redshift behaviour of the dark energy.