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We introduce a semi-analytic galaxy formation model implementing aself-consistent treatment for the hot halo gas configuration and the assemblyof central disks. Using the model, we explore a preventative feedback model, inwhich the circum-halo medium is assumed to be preheated up to a certain entropylevel by early starbursts or other processes, and compare it with an ejectivefeedback model, in which baryons are first accreted into dark matter halos andsubsequently ejected out by feedback. The model demonstrates that when themedium is preheated to an entropy comparable to the halo virial entropy thebaryon accretion can be largely reduced and delayed. In addition, the preheatedmedium can establish an extended low density gaseous halo when it accretes intothe dark matter halos, and result in a specific angular momentum of the coolinggas large enough to form central disks as extended as those observed. Combinedwith simulated halo assembly histories, the preventative feedback model canreproduce remarkably well a number of observational scaling relations. Theseinclude the cold baryon (stellar plus cold gas) mass fraction-halo massrelations, star formation histories, disk size-stellar mass relation and itsevolution, and the number density of low-mass galaxies as a function ofredshift. In contrast, the conventional ejective feedback model fails toreproduce these observational trends. Using the model, we demonstrate that theproperties of disk galaxies are closely tied to the thermal state of hot halogas and even possibly the circum-halo medium, which suggests that observationaldata for the disk properties and circum-galactic hot/warm medium may jointlyprovide interesting constraints for galaxy formation models.

Formation of disk galaxies in preheated media: a preventative feedback model