Semianalytical Models for the Formation of Disk Galaxies. I. Constraints from the Tully‐Fisher Relation

We present new semi-analytical models for the formation of disk galaxies withthe purpose of investigating the origin of the near-infrared Tully-Fisher (TF)relation. The models assume that disks are formed by cooling of the baryonsinside dark halos with realistic density profiles, and that the baryonsconserve their specific angular momentum. Only gas with densities above thecritical density given by Toomre's stability criterion is considered eligiblefor star formation, and a simple recipe for supernovae feedback is included. Weemphasize the importance of extracting the proper luminosity and velocitymeasures from the models, something that has often been ignored in the past.The observed K-band TF relation has a slope that is steeper than simplepredictions based on dynamical arguments suggest. Taking the stability relatedstar formation threshold densities into account steepens the TF relation,decreases its scatter, and yields gas mass fractions that are in excellentagreement with observations. In order for the TF slope to be as steep asobserved, further physics are required. We argue that the characteristics ofthe observed near-infrared TF relation do not reflect systematic variations instellar populations, or cosmological initial conditions, but are governed byfeedback. Finally we show that our models provide a natural explanation for thesmall amount of scatter that makes the TF relation useful as a cosmologicaldistance indicator.Comment: 20 pages, 10 figures. Accepted for publication in Ap