Gravitational Lensing Predictions from Wave Simulations of Fuzzy Dark Matter

Abstract

In the cold dark matter paradigm, ultralight particles are emerging as strong contenders to conventional massive particles. A unique prediction of dark matter comprising such ultralight particles, known as fuzzy dark matter (FDM), is the presence of strong density modulations throughout galactic halos due to wave interference, which—when approximated by a Gaussian random field (GRF)—have been proposed to account for the inability to reproduce the observed positions (when measured at sufficient precisions) and flux ratios of multiply-lensed images of quasars. Here, we predict for the first time the properties of gravitationally lensed images generated from three-dimensional density fields obtained by wave simulations that directly evolve the Schrödinger–Poisson equations. Using a novel framework to project these evolved density fields along various axes of the three-dimensional halo, we obtain the distribution of perturbations to the positions of lensed images. As an exacting test, we find that particles of mass 10−22 eV can reproduce the positions of the quadruply lensed radio jets in system HS 0810+2554 to a level better than that of either the GRF approximation or, to a greater extent, a Navarro–Frenk–White best-fit solution, both of which rely on accurately capturing the global three-dimensional density field of dark matter halos. Our work highlights the importance of wave simulations for making accurate FDM lensing predictions and the potential for high-resolution observations of lensed systems to serve as a direct probe of the nature of dark matter.