Angular cross-correlation of galaxies: a probe of gravitational lensing by large-scale structure

The angular cross-correlation between two galaxy samples separated in redshift is shown to be a useful measure of weak lensing by large-scale structure. Angular correlations in faint galaxies arise as a result of spatial clustering of the galaxies as well as gravitational lensing by dark matter along the line of sight. The lensing contribution to the two-point autocorrelation function is typically small compared with the gravitational clustering. However, the cross-correlation between two galaxy samples is almost unaffected by gravitational clustering provided that their redshift distributions do not overlap. The cross-correlation is then induced by magnification bias resulting from lensing by large-scale structure. We compute the expected amplitude of the cross-correlation for popular theoretical models of structure formation. For two populations. with mean redshifts of similar or equal to 0.3 and 1, we find a crosscorrelation signal of similar or equal to 1 per cent on arcmin scales and similar or equal to 3 per cent on scales of a few arcsec. The dependence on the cosmological parameters Omega and Lambda, the dark matter power spectrum and the bias factor of the foreground galaxy population is explored.