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: ${\log }_{10}(m_{\psi }/\mathrm{eV})=-19.72_{-0.56}^{+0.64}$, and a narrower low-mass window ${\log }_{10}(m_{\psi }/\mathrm{eV})=-21.81_{-0.26}^{+0.39}$, 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.

Accepted for publication in ApJ