The Atacama Cosmology Telescope: DR6 Gravitational Lensing Map and Cosmological Parameters (2304.05203v2)

Abstract: We present cosmological constraints from a gravitational lensing mass map covering 9400 sq. deg. reconstructed from CMB measurements made by the Atacama Cosmology Telescope (ACT) from 2017 to 2021. In combination with BAO measurements (from SDSS and 6dF), we obtain the amplitude of matter fluctuations $\sigma_8 = 0.819 \pm 0.015$ at 1.8% precision, $S_8\equiv\sigma_8({\Omega_{\rm m}}/0.3)^{0.5}=0.840\pm0.028$ and the Hubble constant $H_0= (68.3 \pm 1.1)\, \text{km}\,\text{s}^{-1}\,\text{Mpc}^{-1}$ at 1.6% precision. A joint constraint with CMB lensing measured by the Planck satellite yields even more precise values: $\sigma_8 = 0.812 \pm 0.013$, $S_8\equiv\sigma_8({\Omega_{\rm m}}/0.3)^{0.5}=0.831\pm0.023$ and $H_0= (68.1 \pm 1.0)\, \text{km}\,\text{s}^{-1}\,\text{Mpc}^{-1}$. These measurements agree well with $\Lambda$CDM-model extrapolations from the CMB anisotropies measured by Planck. To compare these constraints to those from the KiDS, DES, and HSC galaxy surveys, we revisit those data sets with a uniform set of assumptions, and find $S_8$ from all three surveys are lower than that from ACT+Planck lensing by varying levels ranging from 1.7-2.1$\sigma$. These results motivate further measurements and comparison, not just between the CMB anisotropies and galaxy lensing, but also between CMB lensing probing $z\sim 0.5-5$ on mostly-linear scales and galaxy lensing at $z\sim 0.5$ on smaller scales. We combine our CMB lensing measurements with CMB anisotropies to constrain extensions of $\Lambda$CDM, limiting the sum of the neutrino masses to $\sum m_{\nu} < 0.13$ eV (95% c.l.), for example. Our results provide independent confirmation that the universe is spatially flat, conforms with general relativity, and is described remarkably well by the $\Lambda$CDM model, while paving a promising path for neutrino physics with gravitational lensing from upcoming ground-based CMB surveys.

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

The paper entitled "The Atacama Cosmology Telescope: DR6 Gravitational Lensing Map and Cosmological Parameters" presents an extensive analysis of gravitational lensing data originating from the Atacama Cosmology Telescope (ACT). Focusing on data collected between 2017 and 2021, this paper outlines crucial findings on cosmological parameters derived from a newly reconstructed mass map covering an area of 9400 square degrees. The cosmological implications of these findings are explored in detail, specifically concerning the amplitude of matter fluctuations ($\sigma_8$), the Hubble constant ($H_0$), and the sum of neutrino masses ($\sum m_{\nu}$). Furthermore, the analysis includes a comparison with existing galaxy and CMB lensing surveys, thereby setting a benchmark for future research in cosmology.

Key Results

The paper presents several significant results with substantial numerical clarity. One of the central findings is the amplitude of matter fluctuations, reported as $\sigma_8 = 0.819 \pm 0.015$, with a precision of 1.8%. When combined with CMB lensing constraints from the ACT lensing map and other datasets, $\sigma_8$ is determined to be $0.812 \pm 0.013$. The constraints on the Hubble constant, $H_0$, indicate a value of $$68.3 \pm 1.1 \, \text{km}\,\text{s}^{-1}\,\text{Mpc}^{-1}$$, providing a strong case for consistency with the $\Lambda$CDM model.

Comparison with prior surveys reveals noteworthy tensions, with the $S_8$ parameter from KiDS, DES, and HSC surveys showing discrepancies with ACT-derived values, ranging from 1.7 to 2.1 sigma lower.

Theoretical and Practical Implications

The paper makes significant contributions to theoretical and practical aspects of cosmology. Theoretical implications revolve around the concordance of these findings with the $\Lambda$CDM model, reinforcing its status as the prevailing cosmological paradigm. Here, the constraints on $\sigma_8$ offer robust checks against early-universe predictions derived from CMB anisotropy data, challenging existing tensions in the field, such as those presented by local universe measurements of the Hubble constant.

On the practical side, the availability of the mass map provides new opportunities for cross-correlation studies with galaxy surveys, potentially elucidating the dark matter structures on linear scales up to redshift $z \sim 0.5-5$. By further refining the measurement of cosmological parameters, this research sets a refined path for neutrino physics, specifically constraining the sum of neutrino masses to less than 0.13 eV (95% confidence level).

Future Directions

The findings from this paper pave the way for future developments in CMB lensing studies, including the refinement of mass maps through additional data and the integration of other cosmological surveys, such as the Simons Observatory. Beyond this, continued exploration into the nature of dark energy, test of spatial curvature, and interactions between dark matter and baryons are critical areas for advancing the field. Anticipated advancements in the sensitivity and angular resolution of forthcoming experiments are expected to dramatically enhance the precision of these cosmological measurements.

In conclusion, this paper represents a significant stride in cosmology, leveraging the ACT DR6 gravitational lensing map to elucidate critical cosmological parameters and offering independent confirmation of a spatially flat universe under the $\Lambda$CDM model. The extensive data release accompanying the research advances opportunities for a wide array of ancillary studies in astrophysics and cosmology.