Tele-Correlation: Calibrating Shear-Shear Correlation with Real Data

TL;DR

This paper introduces a method called tele-correlation to calibrate shear-shear correlations in galaxy shape measurements using real data, revealing significant biases and improving cosmological parameter estimates.

Contribution

It proposes using tele-correlation with single-exposure shear estimators to directly calibrate systematic biases in shear measurements.

Findings

Significant multiplicative biases up to 10% due to redshift binning.

Calibration increases the $S_8$ value by about 1$\sigma$ in the analysis.

Demonstrates the effectiveness of tele-correlation with DECaLS data.

Abstract

Tele-correlation refers to the correlation of galaxy shapes with large angular separations (e.g., $>100$ degrees). Since there are no astrophysical reasons causing such a correlation on cosmological scales, any detected tele-correlation could disclose systematic effects in shear-shear correlation measurement. If the shear estimators are measured on single exposures, we show that the field distortion (FD) signal associated with the galaxy position on the CCD can be retained and used in tele-correlation to help us directly calibrate the multiplicative and additive biases in shear-shear correlations. We use the DECaLS shear catalog produced by the Fourier\_Quad pipeline to demonstrate this idea. To our surprise, we find that significant multiplicative biases can arise (up to more than 10\%) due to redshift binning of the galaxies. Correction for this bias leads to about 1$\sigma$ increase of the best-fit value of $S_8$ from $0.760^{+0.015}_{-0.017}$ to $0.777^{+0.016}_{-0.019}$ in our tomography study.