Corrective lenses for high-redshift supernovae

Weak lensing of high-redshift Type Ia supernovae induces an external dispersion in their observed standard candle brightnesses, comparable in magnitude to the intrinsic dispersion for redshifts z > 1. The same matter fluctuations responsible for the magnification of distant supernovae also generate shear in the images of background galaxies. We investigate the possibility of using lensing shear maps constructed from galaxies surrounding the supernovae as a means of correcting the lensing-induced magnification dispersion. We find that a considerable fraction of the lensing dispersion derives from subarcminute scales, which are not probed by shear maps smoothed on arcminute scales. We thus find that weak-lensing shear maps will be of only limited value in reducing the weak-lensing magnification fluctuations of supernovae.