Weak lensing, Big Magnification: Recovering hidden lensing information from galaxy positions
Abstract
Galaxy clustering and weak gravitational lensing are powerful cosmological probes, traditionally combined through galaxy clustering and galaxy-galaxy lensing in a 2×2pt 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 (z≃0.7-$2.5$) 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 2×2pt 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 S8 constraints comparable to traditional 3×2pt analyses, and tighter for the more precise calibration scenarios considered here. The framework also enables near-zero-response samples for traditional 3×2pt and geometric lensing-ratio analyses. These results motivate further optimization and validation of galaxy selections to realize magnification as a complementary cosmological probe. [Abrg.]
Related
- Why Azimuthal Averaging Works in Halo Lensing: Symmetry and Power Counting for Nonlinear Shear and Magnification
- Recovering Subtle Cosmological Information with the Zel’dovich-inspired Transform
- Finite-source magnification residuals from a cNFW-inspired perturbation of an effective spinning black hole binary lens
- Optimal galaxy magnification: generalized fundamental-plane residuals and number counts are all you need
- Binary-lens amplification of starlight: from magnification flares to quasi-periodic tracking of orbital evolution
BibTeX
@misc{alarcon2026weak,
title = {{Weak lensing, Big Magnification: Recovering hidden lensing information from galaxy positions}},
author = {Alex Alarcon and Carles Sánchez},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.03913},
eprint = {2610.03913},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.03913},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Weak lensing, Big Magnification: Recovering hidden lensing information from galaxy positions
AU - Alex Alarcon
AU - Carles Sánchez
PY - 2026
DA - 2026/10/02
PB - arXiv
DO - 10.48550/arxiv.2610.03913
UR - https://arxiv.org/abs/2610.03913
AB - Galaxy clustering and weak gravitational lensing are powerful cosmological probes, traditionally combined through galaxy clustering and galaxy-galaxy lensing in a 2×2pt 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 (z≃0.7-$2.5$) 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 2×2pt 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 S_8 constraints comparable to traditional 3×2pt analyses, and tighter for the more precise calibration scenarios considered here. The framework also enables near-zero-response samples for traditional 3×2pt and geometric lensing-ratio analyses. These results motivate further optimization and validation of galaxy selections to realize magnification as a complementary cosmological probe. [Abrg.]
ER -