  We compute a general expression for the contribution of vector perturbations
to the redshift-space distortion of galaxy surveys. We show that they
contribute to the same multipoles of the correlation function as scalar
perturbations and should thus in principle be taken into account in data
analysis. We derive constraints for next-generation surveys on the amplitude of
two sources of vector perturbations, namely non-linear clustering and
topological defects. While topological defects leave a very small imprint on
redshift-space distortions, we show that the multipoles of the correlation
function are sensitive to vorticity induced by non-linear clustering. Therefore
future redshift surveys such as DESI or the SKA should be capable of measuring
such vector modes, especially with the hexadecapole which appears to be the
most sensitive to the presence of vorticity.
