Atacama Cosmology Telescope: Multiprobe cosmology with unWISE galaxies and ACT DR6 CMB lensing

We present a joint analysis of the cosmic microwave background (CMB) lensing power spectra measured from the Data Release 6 of the Atacama Cosmology Telescope (ACT) and PR4, cross-correlations between the ACT and lensing reconstruction and galaxy clustering from unWISE, and the unWISE clustering auto-spectrum. We obtain 1.5% constraints on the matter density fluctuations at late times parametrized by the best constrained parameter combination S 8 3 x 2 pt ≡ σ 8 ( Ω m / 0.3 ) 0.4 = 0.815 ± 0.012 . The commonly used S 8 ≡ σ 8 ( Ω m / 0.3 ) 0.5 parameter is constrained to S 8 = 0.816 ± 0.015 . In combination with baryon acoustic oscillation (BAO) measurements we find σ 8 = 0.815 ± 0.012 . We also present sound-horizon-independent estimates of the present day Hubble rate of H 0 = 66.4 − 3.7 + 3.2 km s − 1 Mpc − 1 from our large scale structure data alone and H 0 = 64.3 − 2.4 + 2.1 km s − 1 Mpc − 1 in combination with uncalibrated supernovae from . Using parametric estimates of the evolution of matter density fluctuations, we place constraints on cosmic structure in a range of high redshifts typically inaccessible with cross-correlation analyses. Combining lensing cross- and autocorrelations, we derive a 3.3% constraint on the integrated matter density fluctuations above z = 2.4 , one of the tightest constraints in this redshift range and fully consistent with a Λ cold dark matter ( Λ CDM ) model fit to the primary CMB from . Finally, combining with primary CMB observations and using the extended low redshift coverage of these combined datasets we derive constraints on a variety of extensions to the Λ CDM model including massive neutrinos, spatial curvature, and dark energy. We find in flat Λ CDM ∑ m ν < 0.12 eV at 95% confidence using the large scale structure data, BAO measurements from Sloan Digital Sky Survey, and primary CMB observations.