Image: The soft glow of the Milky Way pours down like a waterfall over the VLT Survey Telescope (VST) at ESO’s Paranal Observatory. Image of VLT Observatory by ESO/Y. Beletsky. KiDS photographer: Samuel Avraham.

Originally designed more than two decades ago, KiDS is a ground-based imaging survey optimized to detect weak gravitational lensing—the subtle distortions in galaxy shapes caused by gravitational forces from large-scale cosmic structures. By mapping these tiny distortions across extensive portions of the sky, researchers can infer how matter, both visible and dark, is distributed throughout the Universe.

The Kilo-Degree Survey (KiDS) 6x2pt Legacy Analysis.

Despite its relatively modest size, the KiDS collaboration has consistently achieved world-class scientific results. While other large-scale cosmological projects such as the Dark Energy Survey (DES) and the Hyper Suprime-Cam (HSC) survey involve hundreds of scientists, KiDS has distinguished itself through the dedicated efforts of a compact and highly focused team.

Image: The group hard at work! Photographer: Samuel Avraham.

Earlier this year, the KiDS team released its Legacy Weak Lensing analysis, providing detailed insights into the long-standing cosmological puzzle known as the S₈ tension—an ongoing discrepancy between the observed growth of cosmic structures and predictions based on the early Universe. The recent 6x2pt analysis directly builds upon this work, integrating weak lensing measurements with galaxy clustering data from KiDS photometry and spectroscopic information from the BOSS survey.

The term “6x2pt” refers to six unique two-point correlation functions involving galaxy positions and shapes, widely recognized as the gold standard method for Stage-III cosmological surveys. These surveys have laid critical groundwork for upcoming Stage-IV missions, including Euclid, LSST, and DESI.

During the OKC workshop, participants actively refined data measurements, enhanced theoretical models, and addressed intricate but crucial details to ensure the completeness of this cosmological analysis. This collaborative effort will leave a lasting scientific legacy and will set important benchmarks for future precision cosmology.

The workshop also emphasized growing collaborations between KiDS and OKC. Notably, master’s student Xander Nooderloos from Utrecht University is currently completing his Master's project at OKC, co-supervised by Prof. Elisa Chisari, a prominent figure in both KiDS and LSST. Nooderloos’ research aligns directly with the themes of the workshop.

Dr. Arthur Loureiro, researcher at OKC and workshop organizer, underscored the wider significance of the recent work: “The tools and methodologies we developed during this week are crucial for my project funded by the Swedish National Space Agency, which aims to measure the mass of the lightest neutrino. The 6x2pt analysis will act as a pathfinder for our future analysis using data from the Euclid mission.”

With next-generation cosmological surveys on the horizon, the KiDS 6x2pt analysis exemplifies how meticulous and collaborative science can significantly advance our understanding of the Universe—even when conducted by a relatively small team.