ABSTRACT

Using ~200,000 quasars and 13 million galaxies from the Sloan Digital Sky survey, we have detected cosmic magnification of the quasar surface density by foreground large scale structure at 8 sigma significance. Our measurement of the galaxy-quasar cross-correlation function exhibits the amplitude, angular dependence and change in sign as a function of the slope of the observed quasar number counts that is expected from magnification bias due to weak gravitational lensing. We further show that observational uncertainties (stellar contamination, Galactic dust extinction, seeing variations and errors in the photometric redshifts) are well controlled and do not significantly affect the lensing signal.