Cosmology seminar: Cosmology from CMB lensing tomography to z=2 with galaxies from the unWISE catalog

Recent measurements of the amplitude of structure from weak lensing surveys suggest that the late-time universe is slightly less clumpy than expected, with the parameter S8 ~10% lower than the best-fit Lambda-CDM value from Planck.  This tension is significant at the ~3 sigma level, and whether it represents new physics or systematics in the measurement remains an open question.  The combination of the galaxy autocorrelation and galaxy-CMB lensing cross-correlation breaks the degeneracy between galaxy bias and sigma8, with different sources of systematics than cosmic shear. The unWISE galaxy-Planck CMB lensing cross correlation, dominated by galaxies at z~1, also favors a low S8, 0.784 ± 0.015, that is 2.4 sigma below the best-fit S8 from Planck. I will discuss this result in relation to the S8 tension, its sources of systematic error, and future prospects for LSS-CMB lensing cross-correlations.