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

Abstract

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 S83x2pt≡σ8(Ωm/0.3)0.4=0.815±0.012. The commonly used S8≡σ8(Ωm/0.3)0.5 parameter is constrained to S8=0.816±0.015. In combination with baryon acoustic oscillation (BAO) measurements we find σ8=0.815±0.012. We also present sound-horizon-independent estimates of the present day Hubble rate of H0=66.4−3.7+3.2 km s−1 Mpc−1 from our large scale structure data alone and H0=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 (ΛCDM) 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 ΛCDM model including massive neutrinos, spatial curvature, and dark energy. We find in flat ΛCDM∑mν<0.12 eV at 95% confidence using the large scale structure data, BAO measurements from Sloan Digital Sky Survey, and primary CMB observations. Published by the American Physical Society 2025