Strong Stellar Diffusion from Wave DM Cosmological Simulation and Potential Unified Origin for dSphs, UFGs, and UDGs

Abstract

Our $ψ$DM simulations predict that stars diffuse throughout dark matter halos over the Hubble time through a random walk driven by the wave perturbations intrinsic to $ψ$DM. The resulting stellar distribution locally follows a Gaussian profile (Sersic index $n=0.5$), as expected from the central limit theorem, expanding as $R_{1/2}(t)\simeq(\hbar/m_ψ)^{0.5}\sqrt{t}$, in good agreement with the core--halo profiles of typical $ψ$DM dwarf spheroidal galaxies. The strength of this diffusion depends on halo mass and the corresponding soliton, naturally producing progressively more diffuse stellar systems in more massive halos. The observed continuity from faint dwarfs and compact dwarf spheroidals to ultra-diffuse galaxies can therefore be interpreted as an age sequence, with later-forming dwarfs experiencing less diffusion and thus remaining smaller and brighter. Stellar scattering arises from the random walk of the soliton, gradually transporting stars from the dense central core into the outer halo, creating the extended stellar envelopes observed around Local Group dwarfs. Rather than being unique to Ultra-Diffuse Galaxies (UDGs), this wave-driven stellar diffusion may provide a unified mechanism explaining galaxy structure across a vast mass range, from ultra-faint dwarfs to the most massive UDGs, without requiring distinct formation channels or "failed galaxy" scenarios. The diffuse stellar halos and globular cluster distributions recently revealed by Euclid may therefore represent direct observational signatures of the granular dynamics of wave dark matter.