Abstract
A number of recent, low-redshift, lensing measurements hint
at a universe in which the amplitude of lensing is lower than that
predicted from the ΛCDM model fit to the data of the Planck
CMB mission. Here we use the auto- and cross-correlation signal of
unWISE galaxies and Planck CMB lensing maps to infer cosmological
parameters at low redshift. In particular, we consider three unWISE
samples (denoted as "blue", "green" and "red") at median
redshifts z ∼ 0.6, 1.1 and 1.5, which fully cover the Dark
Energy dominated era. Our cross-correlation measurements, with
combined significance S/N ∼ 80, are used to infer the amplitude
of low-redshift fluctuations, σ8; the fraction of matter in
the Universe, Ω
m
; and the combination S8 ≡ σ8
(Ω
m
/0.3)0.5 to which these low-redshift lensing
measurements are most sensitive. The combination of blue, green and
red samples gives a value S
m
= 0.784 ± 0.015, that is fully
consistent with other low-redshift lensing measurements and in
2.4σ tension with the CMB predictions from Planck. This is
noteworthy, because CMB lensing probes the same physics as previous
galaxy lensing measurements, but with very different systematics,
thus providing an excellent complement to previous measurements.