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B. Jain (JHU), A.J. Connolly (Pittsburgh), A.S. Szalay (JHU), SDSS Collaboration
Angular correlations in galaxies arise due to spatial clustering of the galaxies as well as gravitational lensing by dark matter along the line-of-sight. The lensing contribution to the 2-point auto-correlation function is typically small compared to the gravitational clustering. However the cross-correlation between two galaxy samples is nearly unaffected by gravitational clustering provided their redshift distributions do not overlap. The cross-correlation is then induced by magnification bias due to lensing by large-scale structure. Its sign can be positive or negative depending on the slope of the number-magnitude relation of the background sample.
Since the cross-correlation is a measure of the convergence, not the shear, it depends on the positions and magnitudes of galaxies but not on their shapes. Thus it is complementary to lensing measurements of the shear, and has different, possibly smaller systematic errors.
We describe an effort to detect magnification bias due to field lensing from the SDSS commissioning data. Photometric redshifts are used to create the foreground and background samples. The number of galaxies and accuracy in the redshift estimate required to measure the signal expected from theoretical models is estimated. Preliminary tests of these ideas are performed using the SDSS commissioning data.