KiDS-i-800: Comparing weak gravitational lensing measurements in same-sky surveys

TL;DR

This study compares weak gravitational lensing measurements from two overlapping KiDS surveys in different bands, introducing null tests to verify measurement consistency across varying observing conditions and redshift calibrations.

Contribution

The paper presents new null tests for assessing the robustness of weak lensing measurements across different survey bands and observing conditions.

Findings

Shear measurements agree within 4% between the two bands.

Galaxy-galaxy lensing signals agree within 7% after redshift calibration.

Null tests confirm measurement consistency despite different observing conditions.

Abstract

We present a weak gravitational lensing analysis of 815 square degree of $i$-band imaging from the Kilo-Degree Survey (KiDS-$i$-800). In contrast to the deep $r$-band observations, which take priority during excellent seeing conditions and form the primary KiDS dataset (KiDS-$r$-450), the complementary yet shallower KiDS-$i$-800 spans a wide range of observing conditions. The overlapping KiDS-$i$-800 and KiDS-$r$-450 imaging therefore provides a unique opportunity to assess the robustness of weak lensing measurements. In our analysis, we introduce two new `null' tests. The `nulled' two-point shear correlation function uses a matched catalogue to show that the calibrated KiDS-$i$-800 and KiDS-$r$-450 shear measurements agree at the level of $1 \pm 4$\%. We use five galaxy lens samples to determine a `nulled' galaxy-galaxy lensing signal from the full KiDS-$i$-800 and KiDS-$r$-450 surveys and find that the measurements agree to $7 \pm 5$\% when the KiDS-$i$-800 source redshift distribution is calibrated using either spectroscopic redshifts, or the 30-band photometric redshifts from the COSMOS survey.