Joint Constraints on Fuzzy and Warm Dark Matter from Satellite Populations of the Milky Way and Andromeda

Abstract We perform a joint analysis of the Milky Way (MW) and Andromeda (M31) satellite populations to constrain the properties of fuzzy dark matter (FDM) and thermal-relic warm dark matter (WDM). We combine MW satellite observations from the Dark Energy Survey and Pan-STARRS1 with M31 satellite data from the Pan-Andromeda Archaeological Survey, and model the corresponding observable satellite populations using the empirical galaxy–halo connection model described in Nadler et al. (2020) together with the appropriate selection functions. Uncertainties in the virial masses of the MW and M31 are incorporated through host-mass priors that linearly scale the relevant model parameters, allowing us to infer the full posterior distributions of all parameters. For the FDM case, we obtain m FDM > 1.74 × 10 −20 eV (95% CL) and m FDM > 1.42 × 10 −20 eV (20:1 posterior ratio). For thermal-relic WDM, we find m WDM > 6.20 keV (95% CL) and m WDM > 5.75 keV (20:1 posterior ratio). These results represent a moderate improvement over MW-only constraints and provide the strongest constraints to date on the FDM and WDM derived from satellite galaxy populations in the Local Group.