The gravitational lensing imprints of DES Y3 superstructures on the CMB: a matched filtering approach

Low density cosmic voids gravitationally lens the cosmic microwave background (CMB), leaving a negative imprint on the CMB convergence $\kappa$. This effect provides insight into the distribution of matter within voids, and can also be used to study the growth of structure. We measure this lensing imprint by cross-correlating the Planck CMB lensing convergence map with voids identified in the Dark Energy Survey Year 3 data set, covering approximately 4,200 deg² of the sky. We use two distinct void-finding algorithms: a 2D void-finder which operates on the projected galaxy density field in thin redshift shells, and a new code, Voxel, which operates on the full 3D map of galaxy positions. We employ an optimal matched filtering method for cross-correlation, using the MICE N-body simulation both to establish the template for the matched filter and to calibrate detection significances. Using the DES Y3 photometric luminous red galaxy sample, we measure A_κ, the amplitude of the observed lensing signal relative to the simulation template, obtaining A_κ = 1.03 ± 0.22 (4.6σ significance) for Voxel and A_κ = 1.02 ± 0.17 (5.9σ significance) for 2D voids, both consistent with LCDM expectations. We additionally invert the 2D void-finding process to identify superclusters in the projected density field, for which we measure A_κ = 0.87 ± 0.15 (5.9σ significance). The leading source of noise in our measurements is Planck noise, implying that data from the Atacama Cosmology Telescope (ACT), South Pole Telescope (SPT) and CMB-S4 will increase sensitivity and allow for more precise measurements.