Magnification effects as measures of large-scale structure

The magnification effects of clustered matter produce variations in the image sizes and number densities of galaxies across the sky. This Letter advocates the use of these effects in wide-field surveys to map large-scale structure and the profiles of galaxy- and cluster-sized halos. The magnitude of the size variation as a function of angular scale is computed, and the signal-to-noise ratio is estimated for different survey parameters. Forthcoming surveys, especially well-designed space-based imaging surveys, will have high signal-to-noise ratios on scales of about 0.'1 to several degrees. Thus, the clustering of matter could be measured on spatial scales of about 50 kpc-100 Mpc. The signal-to-noise ratio is dominated by sample variance rather than shot noise because of the finite number density of galaxies; hence, the accuracy of the measurements will be limited primarily by survey area, sampling strategy, and possible systematics. Methods based on magnification are compared with the use of shape distortions, and the contrasts and complementaries are discussed. Future work, which is needed to plan survey strategy and interpret measurements based on magnification, is outlined.