We present tomographic measurements of structure growth using crosscorrelations of Atacama Cosmology Telescope (ACT) DR6 and Planck cosmic microwave background (CMB) lensing maps with the unWISE Blue and Green galaxy samples, which span the redshift ranges 0.2 ≲
 Award ID(s):
 1713791
 NSFPAR ID:
 10322136
 Date Published:
 Journal Name:
 Journal of Cosmology and Astroparticle Physics
 Volume:
 2021
 Issue:
 12
 ISSN:
 14757516
 Format(s):
 Medium: X
 Sponsoring Org:
 National Science Foundation
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Abstract z ≲ 1.1 and 0.3 ≲z ≲ 1.8, respectively. We improve on prior unWISE crosscorrelations not just by making use of the new, highprecision ACT DR6 lensing maps, but also by including additional spectroscopic data for redshift calibration and by analyzing our measurements with a more flexible theoretical model. We determine the amplitude of matter fluctuations at low redshifts (z ≃ 0.2–1.6), finding using the ACT crosscorrelation alone and ${S}_{8}\equiv {\sigma}_{8}{({\mathrm{\Omega}}_{m}/0.3)}^{0.5}=0.813\pm 0.021$S _{8}= 0.810 ± 0.015 with a combination of Planck and ACT crosscorrelations; these measurements are fully consistent with the predictions from primary CMB measurements assuming standard structure growth. The addition of baryon acoustic oscillation data breaks the degeneracy betweenσ _{8}and Ω_{m}, allowing us to measureσ _{8}= 0.813 ± 0.020 from the crosscorrelation of unWISE with ACT andσ _{8}= 0.813 ± 0.015 from the combination of crosscorrelations with ACT and Planck. These results also agree with the expectations from primary CMB extrapolations in ΛCDM cosmology; the consistency ofσ _{8}derived from our two redshift samples atz ∼ 0.6 and 1.1 provides a further check of our cosmological model. Our results suggest that structure formation on linear scales is well described by ΛCDM even down to low redshiftsz ≲ 1. 
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