The Atacama Cosmology Telescope: DR6 Gravitational Lensing Map and Cosmological Parameters

Abstract

We present cosmological constraints from a gravitational lensing mass map covering 9400 deg2 reconstructed from measurements of the cosmic microwave background (CMB) made by the Atacama Cosmology Telescope (ACT) from 2017 to 2021. In combination with measurements of baryon acoustic oscillations and big bang nucleosynthesis, we obtain the clustering amplitude σ 8 = 0.819 ± 0.015 at 1.8% precision, S 8 ≡ σ 8 ( Ω m / 0.3 ) 0.5 = 0.840 ± 0.028 , and the Hubble constant H 0 = (68.3 ± 1.1) km s−1 Mpc−1 at 1.6% precision. A joint constraint with Planck CMB lensing yields σ 8 = 0.812 ± 0.013, S 8 ≡ σ 8 ( Ω m / 0.3 ) 0.5 = 0.831 ± 0.023 , and H 0 = (68.1 ± 1.0) km s−1 Mpc−1. These measurements agree with ΛCDM extrapolations from the CMB anisotropies measured by Planck. We revisit constraints from the KiDS, DES, and HSC galaxy surveys with a uniform set of assumptions and find that S 8 from all three are lower than that from ACT+Planck lensing by levels ranging from 1.7σ to 2.1σ. This motivates further measurements and comparison, not just between the CMB anisotropies and galaxy lensing but also between CMB lensing probing z ∼ 0.5–5 on mostly linear scales and galaxy lensing at z ∼ 0.5 on smaller scales. We combine with CMB anisotropies to constrain extensions of ΛCDM, limiting neutrino masses to ∑m ν < 0.13 eV (95% c.l.), for example. We describe the mass map and related data products that will enable a wide array of cross-correlation science. Our results provide independent confirmation that the universe is spatially flat, conforms with general relativity, and is described remarkably well by the ΛCDM model, while paving a promising path for neutrino physics with lensing from upcoming ground-based CMB surveys.

The Atacama Cosmology Telescope: A Measurement of the DR6 CMB Lensing Power Spectrum and Its Implications for Structure Growth

“…We discuss our results in Section 9 and conclude in Section 10. This paper is part of a larger set of ACT DR6 papers and is accompanied by two others: Madhavacheril et al (2024) present the released DR6 CMB lensing mass map and explore the consequences for cosmology from the combination and comparison of our measurements with external data; MacCrann et al (2024) investigate the levels of foreground biasesarguably the most significant potential source of systematic errors-and ensure that these are well controlled in our analysis.…”

“…The data used in this analysis initially cover approximately 19,000 deg 2 before Galactic cuts are applied and have a total inverse variance of 0.55 nK −2 for the nighttime data. Figure 3 68 The degeneracy between σ 8 and Ω m prevents strong constraints on either of these parameters individually, and indeed (although we report them in the figure caption) any such constraints derived will depend strongly on the prior ranges; in order to break the degeneracy between these two parameters, we combine with BAO as shown in the companion paper (Madhavacheril et al 2024). 69 In the following, we denote them f030, f040, f090, f150, and f220.…”

“…The gray scale has white corresponding to regions with high matter density and dark corresponding to underdense regions. Our companion paper, Madhavacheril et al (2024), describes this lensing map in detail. We show the fiducial analysis mask in orange, as well as two additional masks used for consistency tests as described in Sections 6.5.6 and 6.5.8.…”

“…is the theory lensing spectrum evaluated for cosmological parameters θ, and  ¢ bb is the baseline covariance matrix. We discussed the construction of the covariance matrix in Section 5.11, while verification of the Gaussianity of the lensing bandpowers can be found in Appendix H. Further corrections to this likelihood are applied when considering joint constraints with CMB power spectra, as described in our companion paper, Madhavacheril et al (2024). These account for the dependence of the normalization of the lensing bandpowers on the true CMB power spectra and of the N 1 correction on both the true CMB and lensing power spectra.…”

“…This lensing spectrum will allow us to perform a stringent test of our cosmological model, comparing our lensing measurements from redshifts z ∼ 0.5-5 with flat-ΛCDM 67 structure growth predictions based on CMB power spectra probing primarily z ∼ 1100. Our lensing power spectrum will also constrain key parameters such as the sum of neutrino masses, the Hubble parameter, and the curvature of the Universe, as explored in our companion paper (Madhavacheril et al 2024).…”