No Catch-22 for Fuzzy Dark Matter: testing substructure counts and core sizes via high resolution cosmological simulations*

Fuzzy Dark Matter (FDM) has recently emerged as an interesting alternative model to the standard Cold Dark Matter (CDM). In this model, dark matter consists of very light bosonic particles with quantum mechanical effects on galactic scales. Since the small-scale behaviour of FDM is completely determined by the mass of the FDM particle, constraining the FDM axion mass remains a crucial test that would allow FDM to be verified or potentially excluded by existing observations. Using the N-body code AX-GADGET, we perform cosmological simulations of FDM that fully model the dynamical effects of the quantum potential throughout cosmic evolution. Through the analysis of FDM volume and high-resolution zoom-in simulations of different FDM particle masses (m_χ ∼ 10⁻²³ − 10⁻²¹ eV), we study how FDM impacts the abundance of substructure and the inner density profiles of dark matter subhalos, respectively. For the first time, using our FDM volume simulations, we provide a fitting formula for the FDM-to-CDM subhalo mass function ratio as a function of the FDM axion mass. Through comparison of our simulation results with observational inferences of the low-mass end of the subhalo mass function and the density profiles of dwarf galaxies surrounding the Milky Way, we will then place a constraint on the FDM axion mass.