Self-interacting Dark Matter in the Center of a Local Group Dwarf Galaxy and Its Satellites

Abstract We present a detailed comparison of a Local Group dwarf galaxy analogue evolved in two cosmological models: the standard cold dark matter (DM) and a self-interacting dark matter (SIDM) model with a velocity-dependent cross section. Both simulations are run with the high-resolution, hydrodynamical LYRA galaxy formation model, allowing us to explore the global and substructure properties of the dwarf in a consistent context. While the overall halo growth, final mass, and subhalo mass functions remain largely unchanged across models, SIDM produces a central DM core extending to ∼1 kpc, which does not significantly vary with the inclusion of baryons. Baryonic properties, however, differ notably. The SIDM model leads to a 25% reduction in stellar mass and retains more gas within the stellar half-mass–radius due to a prolonged quiescent phase in star formation. The stellar distribution is less centrally concentrated, and a population of in situ star clusters form at late times. Substructure analysis reveals fewer luminous satellites and more stellar-only systems in SIDM, driven in part by tidal stripping that affects the DM more than the stars. A subset of satellites undergoes tidal-triggered core collapse after infall, enhancing the diversity of SIDM satellite rotation curves. These differences offer potential observational signatures of SIDM in low-mass galaxies.