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Session 24 - Disks, Bars & Halos.
Oral session, Wednesday, January 07
International Ballroom East,
The problem of decomposing a galaxy rotation curve into disk and dark halo contributions is somewhat controversial because it is degenerate. We present a new constraint on the dark matter density in the inner parts of bright disk galaxies which we derive from the dynamics of barred galaxies. Our N-body simulations of fully self-consistent disk-halo galaxies confirm that a rapidly rotating bar can lose angular momentum to the halo through dynamical friction. We find that bars are slowed down rapidly when the halo is dense, in agreement with previous theoretical predictions, but low density halos, consistent with a maximum disk, do not slow bars much. Current (somewhat meager) observational evidence indicates that bars are rapidly rotating. We therefore conclude that bright barred galaxies, including the Milky Way, are maximum disks. Furthermore, as long as it is valid to assume a unimodal distribution of dark matter halo central densities covering both barred and unbarred galaxies, unbarred galaxies should be maximum disks also.
The interaction of the dark halo with the disk cannot be ignored in theories of warp formation. Seemingly promising models of warps have had to be abandoned when it was discovered that a live halo damps out the warp. We demonstrate a new method of warp generation with N-body simulations in which initially flat disks are warped by a live halo. The halo properties required are entirely plausible.
