GalICS 2.1: a new semianalytic model for cold accretion, cooling,
  feedback and their roles in galaxy formation
  Dekel & Birnboim06 proposed that the mass-scale that separates late-type and
early-type galaxies is linked to the critical halo mass for the propagation of
a stable shock and showed that they could reproduce the observed bimodality
scale for plausible values of the metallicity of the accreted gas and the shock
radius. Here, we take their analysis one step further and present a new
semianalytic model that computes the shock radius from first principles. This
advancement allows us to compute the critical mass individually for each halo.
Separating cold-mode and hot-mode accretion has little effect on the final
galaxy masses if feedback does not preferentially couple to the hot gas. We
also present an improved model for stellar feedback where 70% of the wind mass
is in a cold galactic fountain with a shorter reaccretion timescale at high
masses. The latter is the key mechanism that allows us to reproduce the
low-mass end of the mass function of galaxies over the entire redshift range
0<z<2.5. Cooling must be mitigated to avoid overpredicting the number density
of galaxies with stellar mass greater than a hundred billion Solar masses but
is important to form intermediate-mass galaxies. At virial masses greater than
three hundred billion Solar masses, cold accretion is more important at high z,
where gas is accreted from smaller solid angles, but this is not true at lower
masses because high-z filaments have lower metallicities. Our predictions are
consistent with the observed metallicity evolution of the intergalactic medium
at 0<z<5.
