A method of weak lensing reconstruction through cosmic magnification with multiband photometry information

Abstract

ABSTRACT Weak gravitational lensing induces flux-dependent fluctuations in the observed galaxy number density distribution. This cosmic magnification (magnification bias) effect in principle enables lensing reconstruction alternative to cosmic shear and cosmic microwave background lensing. However, the intrinsic galaxy clustering, which otherwise overwhelms the signal, has hindered its application. Through a scaling relation found by principal component analysis of the galaxy clustering in multiband photometry space, we design a minimum variance linear estimator to suppress the intrinsic galaxy clustering and to reconstruct the lensing convergence map. In combination of the CosmoDC2 galaxy mock and the CosmicGrowth simulation, we test this proposal for an LSST (Large Synoptic Survey Telescope)-like galaxy survey with ugrizY photometry bands. (1) The scaling relation holds excellently at multipole ℓ < 103, and remains reasonably well to ℓ ∼ 3000. (2) The linear estimator efficiently suppresses the galaxy intrinsic clustering, by a factor of ∼102. (3) For galaxies in the photo-z range 0.8 < zκ < 1.2, the reconstructed convergence map is cosmic variance limited per ℓ mode at ℓ < 102, and shot noise limited at $\ell \gtrsim 200$. (4) Its cross-correlation with cosmic shear of galaxies can achieve $\mathrm{ S/N}\gtrsim 200$. When the source redshift of cosmic shear galaxies zγ < zκ, the systematic error is negligible at all investigated scales (ℓ < 3000). When zγ ≥ zκ, the systematic error caused by the residual intrinsic galaxy clustering becomes non-negligible. We discuss possible mitigation of the residual intrinsic galaxy clustering required for accurate measurement at ℓ > 103. This work further demonstrates the potential of lensing measurement through cosmic magnification to enhance the weak lensing cosmology.