Euclid: Galaxy cluster detection through the weak lensing effect: Algorithm assessment and selection

Weak gravitational lensing (WL) offers a powerful way to detect galaxy clusters by directly tracing their total matter content. Its effectiveness increases with the density of background galaxies, a requirement that is now being met by the high sensitivity and wide coverage of current and upcoming large-area surveys. A prime example is the Euclid telescope, which will map approximately 14,000,deg2$ of the sky, measuring the shapes of billions of galaxies and opening a meaningful window for detecting galaxy clusters uniquely through their WL signal. We present the results of nine galaxy cluster detection algorithms in a blind challenge, using 1200,deg^2 of synthetic Euclid-like WL observations from the DEMNUni-Cov simulations. The performance of these methods was assessed by matching their detections to known synthetic clusters with signal-to-noise ratios greater than 2, satisfying the selection cut of $łogten( ) > 13.3 + 1.049,z + 2 , and by adopting two different matching procedures. The purpose of the challenge is to identify and improve strategies for galaxy cluster detection via WL in preparation of the upcoming Euclid data releases. To this end, we pre-selected four methods based on their individual performance and complementary nature. Each pre-selected method adopted a distinct approach: AMICO-WL employing an optimal filtering technique, DoG employing Gaussian filtering, O21 relying on aperture-mass filtering, and W234 applying multi-scale wavelet filtering. Taken together, the results of these methods can be merged to enhance the processing of Euclid data. Individually, these algorithms reach approximately 10% completeness for a mean purity of 90%, while their combination leads to roughly a two-fold improvement in overall performance, exceeding 70% completeness for low-redshift, high-mass clusters. When extrapolating the results of this work to Euclid Data Release 1, we expect to detect approximately 2500 galaxy clusters via weak gravitational lensing.