Measuring dark energy clustering with CMB-galaxy correlations

The integrated Sachs-Wolfe effect in the cosmic microwave background as measured through its correlation with galaxies provides a unique opportunity to study the dynamics of the dark energy through its large scale clustering properties. Ultimately, a deep all-sky galaxy survey out to z~2 can make a ~10σ or ~10% measurement of the correlation and limit ~3% changes in the gravitational potential or total density fluctuation due to dark energy clustering on the Gpc scale. A canonical single scalar field or quintessence model predicts that these clustering effects will appear on the horizon scale with a strength that reflects the evolution of the dark energy density. In terms of a constant equation of state, this would allow tests of the quintessence prediction for models where |1+w|0.05.