Fuzzy Dark Matter and the Impact of Core--Halo Diversity on Its Particle Mass Constraints

Abstract

We investigate how diversity in the core--halo mass relation and the inclusion of higher-order velocity moments affect constraints on the fuzzy dark matter particle mass ($m_\psi$) inferred from the internal kinematics of dwarf galaxies. Using stellar line-of-sight velocities and projected positions for eight Milky Way dwarf spheroidal galaxies, we model their dark matter halos as solitonic cores embedded within outer Navarro--Frenk--White envelopes. We apply both second- and fourth-order Jeans analyses to derive the posterior distribution of $m_\psi$. Our results show that there are two ranges of $m_\psi$ consistent with the observed kinematics: $\log_{10}(m_\psi/\mathrm{eV}) = -19.72^{+0.64}_{-0.56}$, and a narrower low-mass window $\log_{10}(m_\psi/\mathrm{eV}) = -21.81^{+0.39}_{-0.26}$, both within the 68\% credible intervals. The latter becomes prominent only when core--halo diversity is taken into account, which highlights the sensitivity of the inferred fuzzy dark matter particle mass constraints to our understanding of the core--halo relation. Future observations, providing larger stellar samples and more precise kinematic measurements, will be essential for clarifying the allowed parameter space of fuzzy dark matter.