Cosmology from Supernova Magnification Maps

High-z Type Ia supernovae are expected to be gravitationally lensed by the foreground distribution of large-scale structure. The resulting magnification of supernovae is statistically measurable, and the angular correlation of the magnification pattern directly probes the integrated mass density along the line of sight. Measurements of the cosmic magnification of supernovae therefore complement measurements of galaxy shear in providing a direct measure of the clustering of the dark matter. As the surface density of supernovae is typically much smaller than that of sheared galaxies, the two-point correlation function of lensed Type Ia supernovae suffers from significantly increased shot noise. Nevertheless, we find that the magnification map of a large sample of supernovae provides an important cosmological tool. For example, a search over 20 deg2 over 5 years leading to a sample of ~10,000 supernovae would measure the angular power spectrum of cosmic magnification with a cumulative signal-to-noise ratio of ~20. This detection can be further improved once the supernova distance measurements are cross-correlated with measurements of the foreground galaxy distribution. The magnification maps made using supernovae can be used for important cross-checks with traditional lensing shear statistics obtained in the same fields and can help to control systematics.