Multiple Images and Flux Ratio Anomaly of Fuzzy Gravitational Lenses

Abstract

Extremely light bosonic wave dark matter ($\psi$DM) is an emerging dark matter candidate contesting the conventional cold dark matter paradigm and a model subject to intense scrutiny of late. This work for the first time reports testable salient features pertinent to gravitational lenses of $\psi$DM halos. $\psi$DM halos are distinctly filled with large-amplitude, small-scale density fluctuations with $\delta\rho/\rho_{\rm halo}\sim 1$ in form of density granules. This halo yields ubiquitous flux ratio anomalies of a few tens of percent, as is typically found for lensed quasars, and may also produce rare hexad and octad images, for sources located in well-defined caustic zones. We have found new critical features appearing in the highly de-magnified lens center when the halo has sufficiently high surface density near a very compact massive core.