KiDS-1000 catalogue: Weak gravitational lensing shear measurements

TL;DR

KiDS-1000 delivers a comprehensive weak-lensing catalogue based on 1006 deg^2 of imaging, augmented by a SOM-gold photometric-redshift calibration to produce five tomographic bins. The analysis employs lensfit for shear estimation, an advanced Gaia-enhanced PSF model, and a hybrid PSF residual assessment combining PH08 and a first-order systematics model, validated by a suite of null-tests. The study demonstrates that PSF-related systematics are below critical thresholds, with B-modes consistent with noise and the shear-ratio test confirming redshift calibration integrity, enabling robust joint cosmological analyses with BOSS clustering. Overall, KiDS-1000 achieves a robust shear catalogue suitable for combined-probe investigations, while outlining necessary improvements for future, higher-precision surveys.

Abstract

We present weak lensing shear catalogues from the fourth data release of the Kilo-Degree Survey, KiDS-1000, spanning 1006 square degrees of deep and high-resolution imaging. Our `gold-sample' of galaxies, with well-calibrated photometric redshift distributions, consists of 21 million galaxies with an effective number density of $6.17$ galaxies per square arcminute. We quantify the accuracy of the spatial, temporal, and flux-dependent point-spread function (PSF) model, verifying that the model meets our requirements to induce less than a $0.1σ$ change in the inferred cosmic shear constraints on the clustering cosmological parameter $S_8 = σ_8\sqrt{Ω_{\rm m}/0.3}$. Through a series of two-point null-tests, we validate the shear estimates, finding no evidence for significant non-lensing B-mode distortions in the data. The PSF residuals are detected in the highest-redshift bins, originating from object selection and/or weight bias. The amplitude is, however, shown to be sufficiently low and within our stringent requirements. With a shear-ratio null-test, we verify the expected redshift scaling of the galaxy-galaxy lensing signal around luminous red galaxies. We conclude that the joint KiDS-1000 shear and photometric redshift calibration is sufficiently robust for combined-probe gravitational lensing and spectroscopic clustering analyses.

Figures (11)

• Figure 1: $(J-K_{\rm s}, g-i)$ distribution of the full equatorial KiDS-1000 catalogue (colour map) revealing two distinct populations, compared to the distribution of objects identified as point sources (magenta contours enclosing 68% and 95% of the sample). We find that 3% of our point-source sample has colours that are inconsistent with the stellar locus and exclusion criteria from baldry/etal:2010. The significant tail of point-source objects extending beyond $(J-K_{\rm s})>0$ and $(g-i)< 0.5$ have colours that are characteristic of quasars, which are combined with the stellar sample in our point-source catalogue.
• Figure 2: Average KiDS-1000 PSF ellipticity $\epsilon^{\rm PSF}$ (upper panels), the associated standard deviation (middle panels), and the residual PSF ellipticity $\delta \epsilon^{\rm PSF}$ (lower panels) on the OmegaCAM focal plane, for the first (left panels) and second (right panels) components of the ellipticity. We note that colour-scale changes between rows.
• Figure 3: Contributions to the additive systematic, $\delta\xi_+^{\rm sys}(\theta)$, from the PH08 systematics model. The four terms from Eq. (\ref{['eqn:pherror']}), shown in varying shades of blue/green (see legend for details), cause $\langle e_{\rm obs} e_{\rm obs} \rangle$ to deviate from $\langle e_{\rm obs}^{\rm perfect} e_{\rm obs}^{\rm perfect} \rangle$. The total systematic $\delta\xi_+^{\rm sys}$ (red), given by the summation of these four terms, can be compared to the yellow band which encloses half the uncertainty on $\xi_+$, assuming a non-tomographic cosmic shear analysis. As the correlations can be negative, the vertical axis has a symlog scale with black lines indicating the transition from the logarithmic to linear scale. The apparent asymmetry of the error bars (computed via jackknife realisations) is just an artefact of them crossing the log-linear scale boundary. The PH08 systematics model (red) can be compared to the magenta curve, which shows the expected contribution to the cosmic shear signal from the detector-level bias found in 3/32 OmegaCAM CCDs (see Sect. \ref{['sec:flux_additive']}). This figure presents the analysis of the fifth tomographic bin; similar results are obtained for the other bins.
• Figure 4: Average KiDS-1000 PSF ellipticity $\epsilon^{\rm PSF}$ (left panels, divided by a factor of ten) and residual PSF ellipticity $\delta \epsilon ^{\rm PSF}$ (right panels), indicated by the colour bar, as a function of stellar $r$-band magnitude and CCD chip ID. A flux dependence of the PSF residual $\delta \epsilon_1 ^{\rm PSF}$ is seen in CCD chip IDs 15, 21, and 30, indicating the presence of strong detector-level systematics in these three CCDs.
• Figure 5: Counts per pixel for a stacked image centred on cosmic rays detected in dark frames from OmegaCAM THELI CCD ID 15 (also referred to as ESO CCD ID 74). A distortion can be seen along the serial direction to the read-out amplifier, which we interpret as primarily arising from pixel bounce. We note that this effect is found to be significantly lower in all other OmegaCAM detectors.