Prof. Tom Theuns

I will present an analytical model of galaxy formation called IKEA, in which a galaxy's star formation rate balances the increase in its energy due to feedback from massive stars with energy losses associated with cosmological accretion onto its host halo. Such balancing of energies is self-regulating provided the star formation law is such that the star formation rate increases with gas pressure (such a the Kennicutt-Schmidt law, for example), but does not dependent on the details of the star-formation law. The model has four parameters - hence the name - two of which depend on cosmology while the remaining two depend on stars and their interaction with the interstellar medium. Keeping all four parameters constant, IKEA reproduces very accurately the star formation rate as a function of halo mass and redshift in the Eagle cosmological simulation. Other observables, for example the shape and evolution of the galaxy stellar mass function, are also reproduced reasonably well. The onset of AGN feedback is shown to be a consequence of the failure of stars to regulate cosmological accretion once the potential well of the halo becomes too deep. The characteristic transition scale is set by how much energy is injected in the ISM per solar mass of star formed. The relative success of the model demonstrates that star-forming galaxies are shaped by the balance between stellar feedback and cosmological accretion onto their host halos, with accurately accounting for radiative losses associated with supernova feedback the most crucial ingredient of any model. Time permitting, I will also talk about the recent extension of the model to incorporate Lyman-limit and Damped Lyman-alpha systems.