The Atacama Cosmology Telescope: Cosmology from Cross-correlations of unWISE Galaxies and ACT DR6 CMB Lensing
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Date
2024
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Abstract
We present tomographic measurements of structure growth using cross-correlations of Atacama Cosmology Telescope (ACT) DR6 and Planck cosmic microwave background (CMB) lensing maps with the unWISE Blue and Green galaxy samples, which span the redshift ranges 0.2 less than or similar to z less than or similar to 1.1 and 0.3 less than or similar to z less than or similar to 1.8, respectively. We improve on prior unWISE cross-correlations not just by making use of the new, high-precision ACT DR6 lensing maps, but also by including additional spectroscopic data for redshift calibration and by analyzing our measurements with a more flexible theoretical model. We determine the amplitude of matter fluctuations at low redshifts (z similar or equal to 0.2-1.6), finding S 8 equivalent to sigma 8 ( Omega m / 0.3 ) 0.5 = 0.813 +/- 0.021 using the ACT cross-correlation alone and S 8 = 0.810 +/- 0.015 with a combination of Planck and ACT cross-correlations; these measurements are fully consistent with the predictions from primary CMB measurements assuming standard structure growth. The addition of baryon acoustic oscillation data breaks the degeneracy between sigma 8 and Omega m , allowing us to measure sigma 8 = 0.813 +/- 0.020 from the cross-correlation of unWISE with ACT and sigma 8 = 0.813 +/- 0.015 from the combination of cross-correlations with ACT and Planck. These results also agree with the expectations from primary CMB extrapolations in Lambda CDM cosmology; the consistency of sigma 8 derived from our two redshift samples at z similar to 0.6 and 1.1 provides a further check of our cosmological model. Our results suggest that structure formation on linear scales is well described by Lambda CDM even down to low redshifts z less than or similar to 1.