The roles of feedback in galaxy formation

Takashi Okamoto (Hokkaido University)


Cosmological hydrodynamic simulations are a powerful tool for studying non-linear formation processes of galaxies. Studies using cosmological galaxy formation simulations have revealed that “feedback”, which is the process that gives energy and/or momentum to gas from stars and active galactic nuclei, plays crucial roles in galaxy formation. The feedback mostly solves the small-scale discrepancies between the CDM model and observations. On the larger mass scale, feedback powered by active galactic nuclei (AGN feedback) is needed to quench star formation in massive galaxies. I explain how different feedback processes operate on different mass scales of galaxies and shape the galaxy stellar mass function. Although the simulations now successfully explain many observed properties of galaxies, the inclusion of AGN feedback makes the mass-metallicity relation inconsistent with the observation. This discrepancy indicates that our understanding of galaxy formation is still incomplete. Finally, I show some recent attempts to minimize the use of phenomenological subgrid models in simulations.