Weak lensing, Big Magnification: Recovering hidden lensing information from galaxy positions
arXiv:2610.03913
Abstract
Galaxy clustering and weak gravitational lensing are powerful cosmological probes, traditionally combined through galaxy clustering and galaxy-galaxy lensing in a pt analysis. An alternative is the foreground-background clustering cross-correlation induced by lensing magnification, but measurements have achieved lower signal-to-noise than shear-based lensing. We show that, for deep photometric samples, cancellation between galaxies with positive and negative magnification responses can suppress this signal. Using DES Year 6 photometry and Balrog synthetic-source injections, we explore high-redshift (-) samples split by the sign and amplitude of their magnification response. This separation reduces cancellation and can increase both signal-to-noise and cosmological constraining power. We call the combination of foreground clustering and foreground-background cross-correlations with response-selected background samples BigMag. Forecasts with DES-like simulated data vectors show that, for an optimistic sample configuration and sufficiently precise response calibration, BigMag can achieve constraining power comparable to traditional pt using galaxy positions alone. The same samples also enhance inverse galaxy-galaxy lensing (IGGL), a position-shear correlation dominated by magnification when the position sample lies behind the shape sample. Combining BigMag and IGGL further self-calibrates the magnification responses and yields marginalized constraints comparable to traditional pt analyses, and tighter for the more precise calibration scenarios considered here. The framework also enables near-zero-response samples for traditional pt and geometric lensing-ratio analyses. These results motivate further optimization and validation of galaxy selections to realize magnification as a complementary cosmological probe. [Abrg.]
39 pages, 19 figures, 5 tables, 4 appendices