  Optical weak lensing surveys have become a powerful tool for precision
cosmology, but remain subject to systematic effects that can severely bias
cosmological parameter estimates if not carefully removed. We discuss the
possibility of performing complementary weak lensing surveys at radio/microwave
frequencies, using detections of CO-emitting galaxies with resolved continuum
images from ngVLA. This method has completely different systematic
uncertainties to optical weak lensing shear measurements (e.g. in terms of
blending, PSF, and redshift uncertainties), and can provide additional
information to help disentangle intrinsic alignments from the cosmological
shear signal. A combined analysis of optical and CO galaxy lensing surveys
would therefore provide an extremely stringent validation of highly-sensitive
future surveys with Euclid, LSST, and WFIRST, definitively rejecting biases due
to residual systematic effects. A lensing survey on ngVLA would also provide
valuable spectral (kinematic) and polarimetric information, which can be used
to develop novel cosmological analyses that are not currently possible in the
optical.
