Abstract
We report the first detection of gravitational lensing due to galaxy clusters
using only the polarization of the cosmic microwave background (CMB). The
lensing signal is obtained using a new estimator that extracts the lensing
dipole signature from stacked images formed by rotating the cluster-centered
Stokes $Q/U$ map cutouts along the direction of the locally measured background
CMB polarization gradient. Using data from the SPTpol 500 deg$^2$ survey at
the locations of roughly 18,000 clusters with richness $10$ from
the Dark Energy Survey (DES) Year-3 full galaxy cluster catalog, we detect
lensing at $4.8\sigma$. The mean stacked mass of the selected sample is found
to be $(1.43 0.4)\ 10^14\ M_ødot$ which is in good
agreement with optical weak lensing based estimates using DES data and
CMB-lensing based estimates using SPTpol temperature data. This measurement is
a key first step for cluster cosmology with future low-noise CMB surveys, like
CMB-S4, for which CMB polarization will be the primary channel for cluster
lensing measurements.
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