  We report on investigations of the power of next generation cosmic microwave
background and large scale structure surveys in constraining the nature of dark
energy through the cross-correlation of the Integrated Sachs Wolfe effect and
the galaxy distribution. First we employ a signal to noise analysis to find the
most appropriate properties of a survey in order to detect the correlated
signal at a level of more than 4 sigma: such a survey should cover more than
35% of the sky, the galaxy distribution should be probed with a median redshift
higher than 0.8, and the number of galaxies detected should be higher than a
few per squared arcmin. We consider the forthcoming surveys DUNE, LSST, SNAP,
PanSTARRS. We then compute the constraints that the DUNE survey can put on the
nature of dark energy (through different parametrizations of its equation of
state) with a standard Fisher matrix analysis. We confirm that, with respect to
pure CMB constraints, cross-correlation constraints help in breaking
degeneracies among the dark energy and the cosmological parameters. Naturally,
the constraining capability is not independent of the choice of the dark energy
model. Despite being weaker than some other probes (like Gravitational
Weak-Lensing), these constraints are complementary to them, being sensitive to
the high-redshift behaviour of the dark energy.
