Lawrence Berkeley National Laboratory

CMB photons redshift and blueshift as they move through gravitational potentials $\Phi$ while propagating across the Universe. If the potential is not constant in time, the photons will pick up a net redshift or blueshift, known as the Integrated Sachs-Wolfe (ISW) effect. In the $z \ll 1000$ universe, $\dot{\Phi}$ is nonzero on large scales when the Universe transitions from matter to dark energy domination. This effect is only detectable in cross-correlation with large-scale structure at $z \sim 1$. In this paper we present a 3.2$\sigma$ detection of the ISW effect using cross-correlations between unWISE infrared galaxies and Planck CMB temperature maps. We use 3 tomographic galaxy samples spanning $0 < z < 2$, allowing us to fully probe the dark energy domination era and the transition into matter domination. This measurement is consistent with $\Lambda$CDM ($A_{\rm ISW} = 0.96 \pm 0.30$). We study constraints on a particular class of dynamical dark energy models (where the dark energy equation of state is different in matter and dark energy domination), finding that unWISE-ISW improves constraints from type Ia supernovae due to improved constraints on the time evolution of dark energy. When combining with BAO measurements, we obtain the tightest constraints on specific dynamical dark energy models. In the context of a phenomenological model for freezing quintessence, the Mocker model, we constrain the dark energy density within 10% at $z < 2$ using ISW, BAO and supernovae. Moreover, the ISW measurement itself provides an important independent check when relaxing assumptions about the theory of gravity, as it is sensitive to the gravitational potential rather than the expansion history.