Anatoly Klypin (New Mexico State University)
"Secular bar formation in galaxies with significant amount of dark matter"
ABSTRACT
Using high resolution N-body simulations of stellar disks embedded in
cosmologically motivated dark matter halos, we study the evolution of
bars and the transfer of angular momentum between halos and bars. We
find that dynamical friction results in some transfer of angular
momentum to the halo, but the effect is much smaller than previously
found in low resolution simulations and is incompatible with early
analytical estimates. In simulations with millions of particles
reaching a resolution of 20-40 pc, the pattern speed may not change
over billions of years. Our high resolution models produce bars which
are fast rotators, where the ratio of the corotation radius to the bar
major semi-axis lies in the range R =1.2-1.7, marginally compatible
with observational results. In contrast to many previous simulations,
we find that bars are relatively short. As in many observed cases, the
bar major semi-axis is close to the exponential length of the
disk. The transfer of angular momentum between inner and outer parts
of the disk plays a very important role in the secular evolution of
the disk and the bar. The bar formation increases the exponential
length of the disk by a factor of 1.2 -1.5. The transfer substantially
increases the stellar mass in the centre of the galaxy and decreases
the dark matter-to-baryons ratio. As the result, the central 2 kpc
region is always strongly dominated by the baryonic component. At
intermediate 3-10kpc scales the disk is sub-dominant. In summary,
realistic models produce bar structure in striking agreement with
observational results.
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