Formation of disk galaxies in preheated media: a preventative feedback
  model
  We introduce a semi-analytic galaxy formation model implementing a
self-consistent treatment for the hot halo gas configuration and the assembly
of central disks. Using the model, we explore a preventative feedback model, in
which the circum-halo medium is assumed to be preheated up to a certain entropy
level by early starbursts or other processes, and compare it with an ejective
feedback model, in which baryons are first accreted into dark matter halos and
subsequently ejected out by feedback. The model demonstrates that when the
medium is preheated to an entropy comparable to the halo virial entropy the
baryon accretion can be largely reduced and delayed. In addition, the preheated
medium can establish an extended low density gaseous halo when it accretes into
the dark matter halos, and result in a specific angular momentum of the cooling
gas large enough to form central disks as extended as those observed. Combined
with simulated halo assembly histories, the preventative feedback model can
reproduce remarkably well a number of observational scaling relations. These
include the cold baryon (stellar plus cold gas) mass fraction-halo mass
relations, star formation histories, disk size-stellar mass relation and its
evolution, and the number density of low-mass galaxies as a function of
redshift. In contrast, the conventional ejective feedback model fails to
reproduce these observational trends. Using the model, we demonstrate that the
properties of disk galaxies are closely tied to the thermal state of hot halo
gas and even possibly the circum-halo medium, which suggests that observational
data for the disk properties and circum-galactic hot/warm medium may jointly
provide interesting constraints for galaxy formation models.
