Date Published:March 1, 1996
We use Monte Carlo realizations of halo formation histories and aspherical accretion model to calculate the expected scatter in thevelocity dispersions of galactic halos of a given mass due todifferences in their formation times. Assuming that the rotationalvelocity of a spiral galaxy is determined by the velocity dispersion ofits halo and that its luminosity is related to its total baryonic mass,this scatter translates to a minimum intrinsic scatter in theTully-Fisher relation. For popular cosmological models we find that thescatter due to variations in formation histories is by itself greaterthan allowed by observations. Unless halos of spiral galaxies formed athigh redshift (z 1) and did not later accrete any significant amount ofmass, the Tully-Fisher relation is not likely to be the direct result ofcosmological initial conditions but rather a consequence of a subsequentfeedback process.