The Atacama Cosmology Telescope: high-redshift measurement of structure growth from the cross-correlation of Quaia quasars and CMB lensing from ACT DR6 and Planck PR4

Journal article

We measure the amplitude of matter fluctuations over a wide range of redshifts by combining CMB lensing observations from ACT DR6 and Planck PR4 with the overdensity of quasars from Quaia, a Gaia and unWISE quasar catalog. Our analysis includes the CMB lensing power spectrum from ACT DR6, the auto-correlation of two Quaia quasar samples centered at z ≃ 1.0 and z ≃ 2.1, and their cross-correlations with CMB lensing from both ACT DR6 and Planck PR4. By performing a series of contamination and systematic null tests, we find no evidence for contamination in the lensing maps, contrary to what was suggested in previous Quaia cross-correlation analyses using Planck PR4 CMB lensing data. From the joint analysis of the quasar auto- and cross-correlations with CMB lensing, and including BOSS BAO data to break the degeneracy between Ω m and σ 8, we obtain σ 8 = 0.802+0.045 -0.057, consistent with ΛCDM predictions from Planck primary CMB measurements. We also find consistent results using DESI BAO data. Combining the CMB lensing auto-spectrum with the cross-correlation measurement improves the constraint on σ 8 by 12% relative to the lensing auto-spectrum alone, yielding σ 8 = 0.804 ± 0.013. This dataset combination also enables a reconstruction of structure growth across redshifts. We infer a 12% constraint on the amplitude of matter fluctuations at z > 3, with a measurement at the median redshift of the signal of σ 8(z̃ = 5.1) = 0.146+0.021 -0.014, consistent with Planck at the 1.4σ level. These results provide one of the highest redshift constraints on the growth of structure to date.

Authors: Embil Villagra, C; Farren, G; Fabbian, G; Bolliet, B; Abril-Cabezas, I

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: IOP Publishing
• Journal: Journal of Cosmology and Astroparticle Physics
• Volume: 2025
• Issue: 12
• Pages: 033-033
• Article number: 033
• Publication date: 2025-12-12
• Acceptance date: 2025-10-14
• DOI: 10.1088/1475-7516/2025/12/033
• EISSN: 1475-7516
• ISSN: 1475-7516
• Language: English
• Keywords: cosmological parameters from LSS; galaxy clustering; gravitational lensing