Halo Response to Galaxy Formation
“Flat” rotation curves appear to require correlations between the parameters of the disk and halo of typical galaxies. These correlations can arise naturally when a disk forms by slow accretion within a pre-existing dark halo. As the disk grows, the inner part of the halo responds to the changing gravitational field. The resulting correlation gives a factor of ~ 2 relief from the “fine tuning” problem posed by flat rotation curves. Models with large initial halo core radii (\(r_c^0 \) ≳ 8α-1) give approximately flat rotation curves over the widest range of disk mass. Such large ro c imply that most of the halo orbits contributing to the mass within the optical radius of the galaxy have large radial excursion, extending to much greater r. Consequently, approximations based on circular orbits fail to correctly describe the halo response, and the disk has little effect on the shape of the halo.
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