A high-resolution view of the source-plane magnification near cluster caustics in wave dark matter models

We present the highest-resolution images to date of caustics formed by wave dark matter ( ψ DM) fluctuations near the critical curves of cluster gravitational lenses. We describe the basic magnification features of ψ DM in the source plane at high macromodel magnification and discuss specific differences between the ψ DM and standard cold dark matter (CDM) models. The unique generation of demagnified counterimages (with respect to the magnification from the smooth macromodel) formed outside the Einstein radius for ψ DM is highlighted. Substructure in CDM cannot generate demagnified images with positive parity and thus does not provide a definitive way to distinguish ψ DM from CDM. Highly magnified background sources with sizes r ≈ 1 pc, or approximately a factor of ten smaller than the expected de Broglie wavelength of ψ DM, offer the best possibility for discriminating between ψ DM and CDM. These include objects such as very compact stellar clusters at high redshift, which JWST is finding in abundance.