Probing Multi-formation Channels of Dark Matter-Deficient Galaxies in a Simulated Universe

We investigate the formation and evolution of dark matter-deficient galaxies (DMDGs) using the IllustrisTNG100 cosmological hydrodynamical simulation. We define DMDGs as systems with a dark matter-to-stellar mass ratio below unity, and find two formation channels. In the first, galaxies that initially form within massive dark matter halos lose the majority of their dark matter and transition into DMDGs (acquired DMDGs). In the second, galaxies form with little or no dark matter from the beginning (inborn DMDGs). The two populations show distinct physical properties. Acquired DMDGs exhibit significant temporal variations in mass content, size, and kinematics, whereas inborn DMDGs show mild evolution. The former population tends to form closer to their nearest neighbor galaxies in large-scale overdense regions than the latter population does. We find that most stars in the inborn DMDGs form in situ. Their precursor gas is already metal-enriched and associated with other galaxies before formation. Tidal interactions and filamentary gas flows may contribute to the assembly of compact gas clumps, suggesting multiple formation pathways for inborn DMDGs. Our findings support the idea that there are at least two distinct channels to make galaxies dark matter deficient, which is important for understanding the formation mechanisms of these extreme systems.