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arXiv · 2503.24269

A direct detection method of galaxy intrinsic ellipticity-gravitational shear correlation in non-linear regimes using self-calibration

Avijit Bera·Leonel Medina Varela·Vinu Sooriyaarachchi·Mustapha Ishak·Carter Williams·The LSST Dark Energy Science Collaboration
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Abstract

Intrinsic alignment (IA) of galaxies is a challenging source of contamination in the Cosmic shear (GG) signals. The galaxy intrinsic ellipticity-gravitational shear (IG) correlation is generally the most dominant component of such contamination for cross-correlating redshift bins. The self-calibration (SC) method is one of the most effective techniques to mitigate such contamination from the GG signal. In a photometric survey, the SC method first extracts the galaxy number density-galaxy intrinsic ellipticity (gI) correlation from the observed galaxy-galaxy lensing correlation using the redshift dependence of lens-source pairs. The IG correlation is computed through a scaling relation using the gI correlation and other lensing observables. We extend the SC method beyond the linear regime by modifying its scaling relation which can account for the non-linear galaxy bias model and various IA models. In this study, we provide a framework to detect the IG correlation for the redshift bins for source galaxies for the proposed year 1 survey of the Rubin Legacy Survey of Space and Time (LSST Y1). We tested the method for the tidal alignment and tidal torquing (TATT) model of IA and we found that the scaling relation is accurate within 10$\%$ and 20$\%$ for cross-correlating and auto-correlating redshift bins, respectively. Hence the suppression of IG contamination can be accomplished with a factor of 10 and 5, for cross-correlating and auto-correlating redshift bins, respectively. We tested the method's robustness and found that the suppression of IG contamination by a factor of 5 is still achievable for all combinations of cross-correlating bins even with the inclusion of a moderate amount of uncertainties on IA and bias parameters, respectively. [Abridged]

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Avijit Bera, Leonel Medina Varela, Vinu Sooriyaarachchi, Mustapha Ishak, Carter Williams, The LSST Dark Energy Science Collaboration. 2025-03-31. A direct detection method of galaxy intrinsic ellipticity-gravitational shear correlation in non-linear regimes using self-calibration. https://doi.org/10.1088/1475-7516%2F2025%2F09%2F038

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