The $I\kappa\epsilon\alpha$ model of feedback-regulated galaxy formation
  We present the $I\kappa\epsilon\alpha$ model of galaxy formation, in which a
galaxy's star formation rate is set by the balance between energy injected by
feedback from massive stars and energy lost by the deepening of the potential
of its host dark matter halo due to cosmological accretion. Such a balance is
secularly stable provided that the star formation rate increases with the
pressure in the star forming gas. The $I\kappa\epsilon\alpha$ model has four
parameters that together control the feedback from star formation and the
cosmological accretion rate onto a halo. $I\kappa\epsilon\alpha$ reproduces
accurately the star formation rate as a function of halo mass and redshift in
the EAGLE hydrodynamical simulation, even when all four parameters are held
constant. It predicts the emergence of a star forming main sequence along which
the specific star formation rate depends weakly on stellar mass with an
amplitude that increases rapidly with redshift. We briefly discuss the emerging
mass-metallicity relation, the evolution of the galaxy stellar mass function,
and an extension of the model that includes feedback from active galactic
nuclei (AGN). These self-regulation results are independent of the star
formation law and the galaxy's gas content. Instead, star forming galaxies are
shaped by the balance between stellar feedback and cosmological accretion, with
accurately accounting for energy losses associated with feedback a crucial
ingredient.
