The Atacama Cosmology Telescope DR6 and DESI: structure formation over cosmic time with a measurement of the cross-correlation of CMB lensing and luminous red galaxies
Authors: Kim Joshua , Sailer Noah , Madhavacheril Mathew S. , Ferraro Simone , Abril-Cabezas Irene , Aguilar Jessica Nicole , Ahlen Steven , Richard Bond J. , Brooks David , Burtin Etienne , Calabrese Erminia , Chen Shi-Fan , Choi Steve K. , Claybaugh Todd , Darwish Omar , de la Macorra Axel , DeRose Joseph , Devlin Mark , Dey Arjun , Doel Peter , Dunkley Jo , Embil-Villagra Carmen , Farren Gerrit S. , Font-Ribera Andreu , Forero-Romero Jaime E. , Gaztañaga Enrique , Gluscevic Vera , Gontcho Satya Gontcho A. , Guy Julien , Honscheid Klaus , Howlett Cullan , Kirkby David , Kisner Theodore , Kremin Anthony , Landriau Martin , Guillou Laurent Le , Levi Michael E. , MacCrann Niall , Manera Marc , Marques Gabriela A. , Meisner Aaron , Miquel Ramon , Moodley Kavilan , Moustakas John , Newburgh Laura B. , Newman Jeffrey A. , Niz Gustavo , Orlowski-Scherer John , Palanque-Delabrouille Nathalie , Percival Will J. , Prada Francisco , Qu Frank J. , Rossi Graziano , Sanchez Eusebio , Schaan Emmanuel , Schlafly Edward F. , Schlegel David , Schubnell Michael , Sehgal Neelima , Seo Hee-Jung , Shaikh Shabbir , Sherwin Blake D. , Sifón Cristóbal , Sprayberry David , Staggs Suzanne T. , Tarlé Gregory , van Engelen Alexander , Weaver Benjamin Alan , Wenzl Lukas , White Martin , Wollack Edward J. , Yèche Christophe , Zou Hu 
Published: December 2024

Abstract
We present a high-significance cross-correlation of CMB lensing maps from the Atacama Cosmology Telescope (ACT) Data Release 6 (DR6) with luminous red galaxies (LRGs) from the Dark Energy Spectroscopic Instrument (DESI) Legacy Survey spectroscopically calibrated by DESI. We detect this cross-correlation at a significance of 38σ; combining our measurement with the Planck Public Release 4 (PR4) lensing map, we detect the cross-correlation at 50σ. Fitting this jointly with the galaxy auto-correlation power spectrum to break the galaxy bias degeneracy with σ
8, we perform a tomographic analysis in four LRG redshift bins spanning 0.4 ≤ z ≤ 1.0 to constrain the amplitude of matter density fluctuations through the parameter combination S
8
× = σ
8 (Ω
m
/ 0.3)0.4. Prior to unblinding, we confirm with extragalactic simulations that foreground biases are negligible and carry out a comprehensive suite of null and consistency tests. Using a hybrid effective field theory (HEFT) model that allows scales as small as k
max = 0.6 h/ Mpc, we obtain a 3.3% constraint on S
8
× = σ
8 (Ω
m
/ 0.3)0.4 = 0.792+0.024
-0.028 from ACT data, as well as constraints on S
8
×(z) that probe structure formation over cosmic time.
Our result is consistent with the early-universe extrapolation from primary CMB anisotropies measured by Planck PR4 within 1.2σ. Jointly fitting ACT and Planck lensing cross-correlations we obtain a 2.7% constraint of S
8
× = 0.776+0.019
-0.021, which is consistent with the Planck early-universe extrapolation within 2.1σ, with the lowest redshift bin showing the largest difference in mean. The latter may motivate further CMB lensing tomography analyses at z < 0.6 to assess the impact of potential systematics or the consistency of the ΛCDM model over cosmic time.