Tele-correlation: calibrating shear-shear correlation with real 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 1σ increase of the best-fit value of S8 from 0.760+0.015-0.017 to 0.777+0.016-0.019 in our tomography study.