A Technique for Weak Lensing with Velocity Maps: Eliminating Ellipticity Noise in Hi Radio Observations

Weak lensing surveys have become a powerful tool for mapping mass distributions and constraining the expansion history of our Universe, but continuum surveys must average over a large number of galaxies to average down the ellipticity noise due to the unknown ellipticity and orientation of the lensed galaxies. This Letter presents a technique for measuring weak lensing with velocity maps that avoids the ellipticity noise. By studying the inherent noise characteristics, we argue this new technique could rival or exceed the sensitivity of traditional continuum observations for upcoming HI radio surveys. Subject headings: gravitational lensing—cosmology: observations—methods: data analysis— techniques: radial velocities—radio lines: galaxies