Weak lensing constraints on the stellar-to-halo mass relation of galaxy groups with simulation-informed scatter

¹ Leiden Observatory, Leiden University, Einsteinweg 55, 2333 CC Leiden, The Netherlands
² Aix-Marseille Université, CNRS, CNES, LAM, Marseille, France
³ Lorentz Institute for Theoretical Physics, Leiden University, PO Box 9506 2300 RA Leiden, The Netherlands

^⋆ Corresponding author: ssli@strw.leidenuniv.nl

Received: 5 November 2024
Accepted: 7 July 2025

Abstract

Understanding the scaling relation between baryonic observables and dark matter halo properties is crucial not only for studying galaxy formation and evolution, but also for deriving accurate cosmological constraints from galaxy surveys. In this paper, we constrain the stellar-to-halo mass relation of galaxy groups identified by the Galaxy and Mass Assembly survey, using weak lensing signals measured by the Kilo-Degree Survey. We compare our measured scaling relation with predictions from the FLAMINGO hydrodynamical simulations and the L-GALAXIES semi-analytical model. We find a general agreement between our measurements and simulation predictions for halos with masses ≳10^13.5 h₇₀⁻¹ M_⊙, but observe slight discrepancies with the FLAMINGO simulations at lower halo masses. We explore improvements to the current halo model framework by incorporating simulation-informed scatter in the group stellar mass distribution as a function of halo mass. We find that including a simulation-informed scatter model tightens the constraints on scaling relations, despite the current data statistics being insufficient to directly constrain the variable scatter. We also test the robustness of our results against different statistical models of miscentring effects from selected central galaxies. We find that accounting for miscentring is essential, but our current measurements do not distinguish among different miscentring models.