Calibrating Photometric Redshift Bias with Lensing Shear Ratios for HSC-Y3 Survey

This research presents an independent calibration of photometric redshift (photo-$z$) distributions for source galaxies in the HSC-Y3 weak lensing survey using small-scale galaxy-galaxy lensing. The method involves measuring the tangential shear around spectroscopic lens galaxies from GAMA, SDSS, and DESI, divided into fifteen narrow redshift bins. Shear ratios are computed to be sensitive to the mean redshift of source galaxies. The analysis derives constraints on the photo-$z$ bias parameters in source bins 2, 3 and 4, achieving signal-to-noise ratios of 59, 75, and 62, respectively. The constraints for Δz_2, Δz_3 and Δz_4 are consistent with those from HSC-Y3 cosmic shear modeling. The study observes a mild shift in the Δz_3–Δz_4 plane due to the heterogeneous depth of the lens sample, which disappears when using only DESI-DR1 lenses. Combining shear-ratio measurements with cosmic shear data, joint constraints on cosmological parameters are obtained: Ω_m = 0.304_{-0.029}^{+0.03} and S_8 = 0.773_{-0.031}^{+0.031}, consistent with cosmic shear-only results.

The use of small-scale lensing as an independent probe for calibrating photometric redshift bias in weak lensing cosmology is a significant contribution. The consistency of the results with HSC-Y3 cosmic shear modeling validates the method. The observation of a shift in the Δz_3–Δz_4 plane due to the heterogeneous depth of the lens sample highlights the importance of careful consideration of systematic effects.

Future research should focus on refining the calibration techniques to address the issue of heterogeneous lens sample depth. Further investigation into the impact of photo-$z$ bias on cosmological parameter estimation is crucial. This research contributes to the ongoing effort to improve the accuracy and precision of weak lensing cosmology.

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