Reconstructed FDM interference as a function of axion mass for an isotropic background density at redshift z = 4. First row: FDM density, |ψ|², as in Eq. (5), i.e., including both the time static and interference term. Second row: The interference term relative to static background density. Strong, 𝒪(1), interference features are observable both in the radial and azimuthal direction, indicative of an isotropic, β = 0, background density. Third row: The wave function phase Arg[ψ]. Quantized vortices (red circles, shown only for the left hand column), another feature unique for FDM, correspond to 2π discontinuities in the phase function, or as described in the main text, places of nonzero vorticity, Eq. (30).