Searching for Dark Structures: A Comparison of Weak-lensing Convergence Maps and Lensing-weighted Galaxy Density Maps

Abstract We present the result of a comparison between the dark matter distribution inferred from weak gravitational lensing and the observed galaxy distribution to identify dark structures with a high dark-matter-to-galaxy density ratio. To do this, we use weak-lensing convergence maps from Dark Energy Survey Year 3 data, and construct corresponding galaxy convergence maps at z ≲ 1.0, representing projected galaxy number density fluctuations weighted by lensing efficiency. The two maps show overall agreement. However, we could identify 22 regions where the dark matter density exhibits an excess compared to the galaxy density. After carefully examining the survey depths and proximity to survey boundaries, we select the seven most probable candidates for dark structures. This sample provides valuable test beds for further investigations into dark matter mapping. Moreover, our method will be very useful for future studies of dark structures as large-scale weak-lensing surveys become available, such as the Euclid mission, the Vera C. Rubin Observatory’s Legacy Survey of Space and Time, and the Nancy Grace Roman Space Telescope.